Canine Oral Melanoma: Questioning the Existing Information through a Series of Clinical Cases

Twelve dogs with oral malignant melanomas (MM) were evaluated in this study, with demographic details indicating a balanced distribution of gender, age, and weight among various breeds. Tumor locations varied, with diverse surgical procedures being performed, including mandibulectomies and maxillectomies. Lymphadenectomies were conducted, revealing a 16.66% metastatic rate in regional lymph nodes. At the time of surgery, clinical staging identified stages I, II, and III, with most cases having non-infiltrated margins and a high mitotic index. Follow-up revealed local recurrences and metastases, prompting additional surgeries and affecting survival rates. This study reports varying outcomes, with some dogs completing one year without recurrence, while others experienced progressive disease, leading to six oral melanoma-related deaths. The characteristics of melanotic melanoma and amelanotic melanoma are observed in order to study differences between them, the degree of aggressiveness, the mortality rate and the possibility of future therapeutic targets. Although high pigmentation has been correlated with a better outcome, we could not find any significant correlation between survival and achromia. Oral benign melanomas might exist, and this could justify variabilities between stage and survival; however, carefulness is required due to their unpredictable behavior. The findings underscore the complexity of oral melanoma cases and highlight the need for further research on effective management strategies.

Review of the comparative pathological and immunohistochemical features of human and canine cutaneous melanocytic neoplasms

Melanocytic neoplasms originate from melanocytes and melanoma, the malignant form, is a common canine neoplasm and the most aggressive human skin cancer. Despite many similarities between these neoplasms in both species, only a limited number of studies have approached these entities in a comparative manner. Therefore, this review compares benign and malignant melanocytic neoplasms in dogs and humans, exclusively those arising in the haired skin, with regard to their clinicopathological, immunohistochemical and molecular aspects. Shared features include spontaneous occurrence, macroscopic features and microscopic findings when comparing human skin melanoma in the advanced/invasive stage and canine cutaneous melanoma, immunohistochemical markers and several histopathological prognostic factors. Differences include the apparent absence of active mutations in the BRAF gene in canine cutaneous melanoma and less aggressive clinical behaviour in dogs than in humans. Further studies are required to elucidate the aetiology and genetic development pathways of canine cutaneous melanocytic neoplasms. Evaluation of the applicability of histopathological prognostic parameters commonly used in humans for dogs are also needed. The similarities between the species and the recent findings regarding genetic mutations in canine cutaneous melanomas suggest the potential utility of dogs as a natural model for human melanomas that are not related to ultraviolet radiation.

Hypoxia-associated markers in the prognosis of oral canine melanoma

Canine oral malignant melanoma (COMM) is the most common neoplasm in the oral cavity characterized by local invasiveness and high metastatic potential. Hypoxia represents a crucial feature of the solid tumor microenvironment promoting cancer progression and drug resistance. Hypoxia-inducible factor-1α (HIF-1α) and its downstream effectors, vascular endothelial growth factor A (VEGF-A), glucose transporter isoform 1 (GLUT1), C-X-C chemokine receptor type 4 (CXCR4), and carbonic anhydrase IX (CAIX), are the main regulators of the adaptive response to low oxygen availability. The prognostic value of these markers was evaluated in 36 COMMs using immunohistochemistry. In addition, the effects of cobalt chloride-mediated hypoxia were evaluated in 1 primary COMM cell line. HIF-1α expression was observed in the nucleus, and this localization correlated with the presence or enhanced expression of HIF-1α-regulated genes at the protein level. Multivariate analysis revealed that in dogs given chondroitin sulfate proteoglycan-4 (CSPG4) DNA vaccine, COMMs expressing HIF-1α, VEGF-A, and CXCR4 were associated with shorter disease-free intervals (DFI) compared with tumors that were negative for these markers (P = .03), suggesting hypoxia can influence immunotherapy response. Western blotting showed that, under chemically induced hypoxia, COMM cells accumulate HIF-1α and smaller amounts of CAIX. HIF-1α induction and stabilization triggered by hypoxia was corroborated by immunofluorescence, showing its nuclear translocation. These findings reinforce the role of an hypoxic microenvironment in tumor progression and patient outcome in COMM, as previously established in several human and canine cancers. In addition, hypoxic markers may represent promising prognostic markers, highlighting opportunities for their use in therapeutic strategies for COMMs.

Melanoma of the dog and cat: consensus and guidelines

Melanoma of the dog and cat poses a clinical challenge to veterinary practitioners across the globe. As knowledge evolves, so too do clinical practices. However, there remain uncertainties and controversies. There is value for the veterinary community at large in the generation of a contemporary wide-ranging guideline document. The aim of this project was therefore to assimilate the available published knowledge into a single accessible referenced resource and to provide expert clinical guidance to support professional colleagues as they navigate current melanoma challenges and controversies. Melanocytic tumors are common in dogs but rare in cats. The history and clinical signs relate to the anatomic site of the melanoma. Oral and subungual malignant melanomas are the most common malignant types in dogs. While many melanocytic tumors are heavily pigmented, making diagnosis relatively straightforward, melanin pigmentation is variable. A validated clinical stage scheme has been defined for canine oral melanoma. For all other locations and for feline melanoma, TNM-based staging applies. Certain histological characteristics have been shown to bear prognostic significance and can thus prove instructive in clinical decision making. Surgical resection using wide margins is currently the mainstay of therapy for the local control of melanomas, regardless of primary location. Radiotherapy forms an integral part of the management of canine oral melanomas, both as a primary and an adjuvant therapy. Adjuvant immunotherapy or chemotherapy is offered to patients at high risk of developing distant metastasis. Location is the major prognostic factor, although it is not completely predictive of local invasiveness and metastatic potential. There are no specific guidelines regarding referral considerations for dogs with melanoma, as this is likely based on a multitude of factors. The ultimate goal is to provide the best options for patients to extend quality of life and survival, either within the primary care or referral hospital setting.

Suspected Primary Intracranial Melanoma with Widespread Distant Metastases in a Cat

An 8-year-old female Domestic Shorthair presented with signs of intracranial disease. Magnetic resonance imaging (MRI) of the head showed an extra-axial space-occupying mass within the cranial vault with a similar intensity lesion within the overlying temporalis muscle. Postmortem examination found masses within the head, lung, liver, spleen, and kidney consistent with malignant melanoma. Intracranial melanoma is rarely reported in cats and is typically only seen as a metastatic lesion associated with an ocular mass. Melanomas can be readily recognised on MRI as they are one of the few lesions which are hyperintense on T1-weighted images.

E-Cadherin Immunostaining in Equine Melanocytic Tumors

Melanocytic tumors are an important neoplastic disease in human and veterinary medicine, presenting large differences regarding tumor behavior between species. In horses, these tumors present a prolonged benign behavior, with rare invasiveness and metastases. In humans and small animals, invasion and metastasis have been associated with an Epithelial-Mesenchymal Transition, where the loss of E-cadherin expression plays a key role in tumor progression. This process and the role of E-cadherin have not yet been evaluated in equine melanocytic tumors. This study aimed to assess the immunolabeling of E-cadherin in equine melanocytic tumors and relate this with clinicopathological variables. A total of 72 equine melanocytic tumors were classified as benign and malignant and evaluated by immunohistochemistry for E-cadherin expression. A different pattern of immunostaining was found, contrasting with other species. A total of 69.4% of tumors presented raised immunolabeling of E-cadherin, with 70.7% of melanomas remaining with high expression. The typical loss of immunostaining was not seen in malignant melanomas and no differences were found between benign and malignant melanomas regarding E-cadherin immunostaining. The high immunolabeling of E-cadherin may contribute to the low invasiveness of these tumors, and it is in accordance with the benign behavior of equine melanoma and with the genetic factors associated with its development.

Expression and Prognostic Evaluation of the Receptor Tyrosine Kinase MET in Canine Malignant Melanoma

The overexpression and activation of the MET receptor tyrosine kinase has been identified in many human malignancies, but its role in canine cancer has only been minimally investigated. In this study we evaluated the expression of MET in two canine malignant melanoma (CMM) cell lines as well as in 30 CMM tissue samples that were collected from the clinical service at our institution. We were able to confirm the expression of the MET protein in both melanoma cell lines, and we demonstrated MET activation by its ligand, HGF, through phosphorylation, in Western blot analysis. We were also able to demonstrate, by immunohistochemistry, the expression of MET in 63% of the tumor tissue samples analyzed, with the majority demonstrating a relatively low expression profile. We then evaluated the association of MET expression scores with histologic parameters, metastasis, and survival. While statistically significant associations were not found across these parameters, an inverse relationship between MET expression levels and time to lymph node versus distant metastasis was suggested in our cohort. These findings may require assessment in a larger group of specimens to further evaluate the role of MET expression in the homing of metastasis in lymph nodes versus that in distant organs.

Mucocutaneous subdermal plexus flap for complete excision of a malignant dermal and conjunctival melanoma in a dog

PURPOSE

To perform a reconstructive blepharoplasty to obtain complete surgical excision of a darkly pigmented raised conjunctival-eyelid mass of the lower eyelid in a dog.

ANIMAL STUDIED

A 7-year-old, female-spayed, Yorkshire Terrier was evaluated for a slowly progressive, dark brown-to-black raised mass of the lower left eyelid. Sampling of the mass via fine-needle aspirate or incisional biopsy was declined, and an excision of the mass with the goal to obtain complete margins and maintain normal eyelid function with cosmesis was elected.

PROCEDURES

The lower palpebral conjunctival-eyelid pigmented mass was excised en bloc and the lower eyelid was reconstructed with a mucocutaneous subdermal plexus flap.

RESULTS

Histopathology revealed a malignant dermal and conjunctivalmelanoma excised with complete margins (1-2 mm). Short-term complications included corneal ulceration and eschar formation, which resolved completely at the 1-month follow-up. Long-term complications included mild trichiasis with epiphora and porphyrin staining. Tumor recurrence was not observed during an 8-month follow-up period.

CONCLUSIONS

The en bloc excision with mucocutaneous subdermal plexus flap was successful in obtaining complete surgical margins for a malignant conjunctival-eyelid melanoma. An excellent functional and cosmetic outcome was achieved without tumor recurrence during an 8-month follow-up period. A mucocutaneous subdermal plexus flap can be considered as a surgical option for malignant melanoma of the lower eyelid.

Canine melanoma: A review of diagnostics and comparative mechanisms of disease and immunotolerance in the era of the immunotherapies

Melanomas in humans and dogs are highly malignant and resistant to therapy. Since the first development of immunotherapies, interest in how the immune system interacts within the tumor microenvironment and plays a role in tumor development, progression, or remission has increased. Of major importance are tumor-infiltrating lymphocytes (TILs) where distribution and cell frequencies correlate with survival and therapeutic outcomes. Additionally, efforts have been made to identify subsets of TILs populations that can contribute to a tumor-promoting or tumor-inhibiting environment, such as the case with T regulatory cells versus CD8 T cells. Furthermore, cancerous cells have the capacity to express certain inhibitory checkpoint molecules, including CTLA-4, PD-L1, PD-L2, that can suppress the immune system, a property associated with poor prognosis, a high rate of recurrence, and metastasis. Comparative oncology brings insights to comprehend the mechanisms of tumorigenesis and immunotolerance in humans and dogs, contributing to the development of new therapeutic agents that can modulate the immune response against the tumor. Therapies that target signaling pathways such as mTOR and MEK/ERK that are upregulated in cancer, or immunotherapies with different approaches such as CAR-T cells engineered for specific tumor-associated antigens, DNA vaccines using human tyrosinase or CGSP-4 antigen, anti-PD-1 or -PD-L1 monoclonal antibodies that intercept their binding inhibiting the suppression of the T cells, and lymphokine-activated killer cells are already in development for treating canine tumors. This review provides concise and recent information about diagnosis, comparative mechanisms of tumor development and progression, and the current status of immunotherapies directed toward canine melanoma.

MELANOCYTIC NEOPLASIA IN PANTHERA SPECIES: CLINICAL PRESENTATIONS, PATHOLOGIC FINDINGS AND RESPONSES TO TREATMENT

Neoplasia is a common cause of morbidity and mortality in captive nondomestic felids. Seven tigers (Panthera tigris), two African lions (Panthera leo), and two snow leopards (Panthera uncia) were diagnosed with melanocytic neoplasia (10 malignant melanomas, two benign melanocytomas) over a 20-yr period. Animals were 10-19 yr old and 5/7 tigers were phenotypically white. Malignant melanoma tumor location included skin (n = 4), oral mucosa (n = 2), nasal planum (n = 1), iris/uvea (n = 2), and lip margin (n = 1); melanocytomas were found in skin (n = 2). Metastasis to regional lymph nodes was seen at diagnosis in 3/7 melanoma cases. Thoracic radiography (n = 6) and/or computed tomography (n = 2) did not detect pulmonary metastasis at diagnosis but were useful for detection later in the disease course. Median survival time (MST) for all cases ranged from 1 mon - 40 mon. Seven cases with malignant melanoma underwent treatment, which included surgery, radiation therapy, and administration of the canine melanoma vaccine (Oncept^®) or a combination of these treatments; MST was 5-40 mon for these cases. While multimodal therapy may provide an improved survival time, the majority of animals with malignant melanoma invariably died from neoplastic disease. Necropsy confirmed metastasis of malignant melanoma in 7/9 animals; sites included lung, liver, lymph node, kidney, mesentery, pleural cavity, heart, stomach, spleen, and adrenal gland. This case series describes the clinical and histologic findings of melanocytic neoplasia in nondomestic felids as well as multimodal treatment strategies incorporating the canine melanoma vaccine.

Diagnosis and histopathologic prognostication of canine melanocytic neoplasms: A consensus of the Oncology-Pathology Working Group

One of the primary objectives of the Oncology Pathology Working Group (OPWG) is for oncologists and pathologists to collaboratively generate consensus documents to standardize aspects of and provide guidelines for veterinary oncologic pathology. Consensus is established through review of relevant peer-reviewed literature relative to a subgroup's particular focus. In this article, the authors provide a critical review of the current literature for the diagnosis of, and histopathologic prognostication for, canine cutaneous and oral/lip melanocytic neoplasms, suggest guidelines for reporting, provide recommendations for clinical interpretation, and discuss future directions. This document represents the opinions of the working group and the authors and does not constitute a formal endorsement by the American College of Veterinary Pathologists, American College of Veterinary Internal Medicine or the Veterinary Cancer Society.

Effects of Para-Toluenesulfonamide on Canine Melanoma Xenotransplants in a BALB/c Nude Mouse Model

Simple Summary

Canine melanomas are malignant neoplasms, and primary melanomas arise at the footpad, nail bed, gastrointestinal tract, mucocutaneous junction, and eyes. Para-toluenesulfonamide (PTS) is a small molecule that acts against several cancers (hepatocellular carcinoma, nonsmall-cell lung cancer, and tongue squamous cell carcinoma). The pharmacological pathway of PTS has the potential to exert anti-inflammatory and antithrombotic functions. We established canine melanoma xenografts in mice and randomized the animals into four treatment groups: saline, cisplatin, PTS, and PTS combined with cisplatin. The findings indicated that compared with the control mice, mice treated with PTS and the combination of PTS and cisplatin showed retarded tumor growth; increased tumor apoptosis through the upregulation of caspase 3 and extracellular signal-regulated kinase phosphorylation; decreased inflammation levels of cytokines, such as interleukin-1β, tumor necrosis factor-α, and interleukin-6; reduced inflammation-related factors, such as the cyclooxygenase-2 protein and nuclear factor-κB mRNA; enhanced anti-inflammation-related factors; and inhibition of the metastasis-related factors transforming growth factor β, CD44, epidermal growth factor receptor, and vascular endothelial growth factor. Combining cisplatin with PTS has a stronger effect than PTS alone. These findings may prove useful in further explorations of the application of PTS or PTS combined with cisplatin to the treatment of canine melanoma in general.

Abstract

The pharmacological pathway of para-toluenesulfonamide (PTS) restricts the kinase activity of the mammalian target of rapamycin, potentially leading to reductions in cell division, cell growth, cell proliferation, and inflammation. These pathways have a critical effect on tumorigenesis. We aimed to examine the antitumor effect of PTS or PTS combined with cisplatin on canine melanoma implanted in BALB/c nude mice by estimating tumor growth, apoptosis expression, inflammation, and metastasis. The mice were randomly divided into four groups: control, cisplatin, PTS, and PTS combined with cisplatin. Mice treated with PTS or PTS combined with cisplatin had retarded tumor growth and increased tumor apoptosis through the enhanced expression of cleaved caspase 3 and extracellular signal-regulated kinase phosphorylation, decreased inflammatory cytokine levels, reduced inflammation-related factors, enhanced anti-inflammation-related factors, and inhibition of metastasis-related factors. Mice treated with PTS combined with cisplatin exhibited significantly retarded tumor growth, reduced tumor size, and increased tumor inhibition compared with those treated with cisplatin or PTS alone. PTS or PTS combined with cisplatin could retard canine melanoma growth and inhibit tumorigenesis. PTS and cisplatin were found to have an obvious synergistic tumor-inhibiting effect on canine melanoma. PTS alone and PTS combined with cisplatin may be antitumor agents for canine melanoma treatment.

Pilot Study: Assessing the Expression of Serum Lactate Dehydrogenase and Peripheral Leukocyte Ratios in Canine Oral Malignant Melanoma

Measurement of blood biomarkers such as lactate dehydrogenase (LDH) and peripheral leukocyte ratios have been shown to be of prognostic value in human melanoma patients. Previous veterinary studies have demonstrated that changes in these values are detectable in multiple canine cancer patients. However, to the authors’ knowledge, no studies have yet demonstrated an increase in LDH in canine oral malignant melanoma patients, nor has the effect of metastasis on LDH levels been explored. This retrospective pilot study included 18 dogs, of which 10 were healthy controls, 5 OMM patients with metastasis and 3 without metastasis. Serum LDH was measured and pre-treatment peripheral leucocyte ratios were calculated. LDH was measurable within all patient groups and a statistically significant difference in LDH levels was detected between patients with OMM and healthy controls (p < 0.05); however, no significant difference was detected between patients with or without metastatic disease. This study suggests that serum LDH levels are significantly increased in dogs with OMM compared to healthy controls, paving the way for further research to investigate the prognostic value of this biomarker.

Tumor-Associated Macrophages in Canine Oral and Cutaneous Melanomas and Melanocytomas: Phenotypic and Prognostic Assessment

The tumor microenvironment is a complex system, where neoplastic cells interact with immune and stromal cells. Tumor-associated macrophages (TAMs) are considered among the most numerically and biologically noteworthy cellular components in tumors and the attention on this cellular population has been growing during the last decade, both for its prognostic role and as a potential future therapeutic target. Melanoma, particularly the oral form, despite being one of the most immunogenic tumors, bears a poor prognosis in dogs and humans, due to its highly aggressive biological behavior and limited therapeutic options. The aims of this study are to characterize and quantify TAMs (using CD163, CD204, Iba1, and MAC387) in canine melanocytic tumors and to evaluate the association of these markers with diagnosis, histologic prognostic features, presence of metastases, and outcome, and to provide preliminary data for possible future therapies targeting TAMs. Seventy-two melanocytic tumors (27 oral melanomas, 25 cutaneous melanomas, 14 cutaneous melanocytomas, and 6 oral melanocytomas) were retrospectively selected and submitted to immunohistochemistry and double immunofluorescence. Double immunolabeling revealed that most CD163⁺ and CD204⁺cells co-expressed Iba1, which labeled also dendritic cells. Iba1 was instead rarely co-expressed with MAC387. Nevertheless, the expression of macrophagic markers showed a mild to moderate association among the four markers, except for CD204 and MAC387. The number of CD163⁺, CD204⁺, and MAC387⁺ cells was significantly higher in oral melanomas compared to oral melanocytomas (p < 0.001; p < 0.05 and p < 0.01, respectively), whereas Iba1 was differentially expressed in cutaneous melanomas and melanocytomas (p < 0.05). Moreover, CD163, IBA1 and MAC387 expression was associated with nuclear atypia and mitotic count. The number of CD163⁺cells was associated with the presence of metastases and tumor-related death in oral melanocytic tumors (p < 0.05 and p = 0.001, respectively).

Multi-institutional retrospective study of canine foot pad malignant melanomas: 20 cases

Melanomas arising from the foot pad are a rare clinical entity in dogs. The biologic behavior of foot pad malignant melanoma is not well understood, and these tumors are infrequently described. The objective of this study was to evaluate the clinical characteristics of primary canine foot pad melanoma in a larger cohort of patients. Eligible cases were solicited from the American College of Veterinary Internal Medicine (ACVIM) Oncology listserv for retrospective review. Included dogs had a cytologic and/or histologic diagnosis of foot pad melanoma evaluated by a board-certified clinical or anatomic pathologist. Dogs with cutaneous, oral, digital, subungual, or interdigital melanomas were excluded. A total of 20 cases were included. Eleven dogs received various adjuvant therapies including chemotherapy, radiation therapy, and/or the ONCEPT canine melanoma vaccine following surgery. At diagnosis, regional lymph node metastasis was observed in four dogs (20%). Seven dogs developed subsequent regional and/or distant metastasis for an overall metastatic rate of 55%. The progression-free interval (PFI) was 101 days (range, 20-960 days). The median survival time (MST) was 240 days (range, 25-479 days). For dogs receiving adjuvant therapy, the MST was 159 days (range, 25-387 days). Canine foot pad melanoma is a rare neoplasm that can exhibit an aggressive behavior.

Treatment of Canine Oral Melanomas: A Critical Review of the Literature

Critical appraisal of the available literature for the treatment of canine oral malignant melanoma (OMM) is lacking. This critical review aimed to evaluate the current literature and provide treatment recommendations and possible suggestions for future canine OMM research. PubMed, Web of Science and Google Scholar were searched in June 2021, for terms relevant to treatment of OMM. Inclusion and exclusion criteria were applied and information on clinical response and outcome extracted. Eighty-one studies were included. The overall level of evidence supporting the various canine OMM treatment options was low. The majority of studies included confounding treatment modalities and lacked randomization, control groups and consistency in reporting clinical response and outcomes. Within these limitations, surgery remains the mainstay of therapy. Adjunctive radiotherapy provided good local control and improved median survival times (MST), chemotherapy did not offer survival benefit beyond that of surgery, while electrochemotherapy may offer a potential alternative to radiotherapy. Immunotherapy holds the most promise in extending MST in the surgical adjunctive setting, in particular the combination of gene therapy and autologous vaccination. Prospective, randomized, double-blinded clinical trials, with a lack of confounding factors and reporting based on established guidelines would allow comparison and recommendations for the treatment of canine OMM.

Diagnosis and Prognosis of Canine Melanocytic Neoplasms

Canine melanocytic neoplasms have a highly variable biological behavior ranging from benign cutaneous melanocytomas to malignant oral melanomas that readily metastasize to lymph nodes and internal organs. This review focuses on the diagnosis and prognosis of canine melanocytic neoplasms. While pigmented melanocytic neoplasms can be diagnosed with fine-needle aspirates, an accurate prognosis requires surgical biopsy. However, differentiating amelanotic spindloid melanomas from soft tissue sarcomas is challenging and often requires immunohistochemical labeling with a diagnostic cocktail that contains antibodies against Melan-A, PNL-2, TRP-1, and TRP-2 as the current gold standard. For questionable cases, RNA expression analysis for TYR, CD34, and CALD can further differentiate these two entities. The diagnosis of amelanotic melanomas will be aided by submitting overlying and/or lateral flanking epithelium to identify junctional activity. Wide excision of lateral flanking epithelium is essential, as lentiginous spread is common for malignant mucosal melanomas. Combining histologic features (nuclear atypia, mitotic count, degree of pigmentation, level of infiltration, vascular invasion; tumor thickness and ulceration) with the Ki67 index provides the most detailed prognostic assessment. Sentinel lymph nodes should be evaluated in cases of suspected malignant melanomas using serial sectioning of the node combined with immunohistochemical labeling for Melan-A and PNL-2.

Canine oral melanoma: a retrospective study of 101 dogs treated with a 6 Gy x 6 radiotherapy protocol

One radiotherapy (RT) protocol used for canine oral melanoma (OM) gives 36 Gy total, in six weekly or biweekly fractions (6 Gy × 6). This retrospective study characterizes oncologic outcomes for a relatively large group of dogs treated with this protocol and determines whether radiation dose intensity (weekly vs. biweekly) affected either progression‐free or overall survival (PFS and OS). Dogs were included if 6 Gy × 6 was used to treat grossly evident OM, or if RT was used postoperatively in the subclinical disease setting. Kaplan–Meier statistics and Cox regression modelling were used to determine the predictive or prognostic value of mitotic count, bony lysis, World Health Organization (WHO) stage (I, II, III, or IV), using systemic anti‐cancer therapies, tumour burden at the time of RT (macroscopic vs. subclinical), radiation dose intensity (weekly vs. biweekly), and treatment planning type (manual vs. computerized). The median PFS and OS times for all dogs (n = 101) were 171 and 232 days, respectively. On univariate analysis PFS and OS were significantly longer (p = <.05) with subclinical tumour burden, WHO stages I or II, and weekly irradiation. On multivariable analysis, only tumour stage remained significant; therefore, cases were grouped by WHO stage (I/II vs. III/IV). With low WHO stage (I/II), PFS and OS were longer when irradiating subclinical disease (PFS: risk ratio = 0.449, p = .032; OS: risk ratio = 0.422, p = .022); this was not true for high WHO stage (III/IV). When accounting for other factors, radiation dose intensity had no measurable impact on survival in either staging group.

Prognostic impact of bone invasion in canine oral malignant melanoma treated by surgery and anti-CSPG4 vaccination: A retrospective study on 68 cases (2010-2020)

Prognosis of canine oral malignant melanoma encompasses clinical, histological and immunohistochemical parameters. The aim of this study was to evaluate the prognostic impact of bone invasion in oral canine melanoma. Sixty-eight dogs bearing oral melanoma staged II and III that underwent surgery and anti-CSPG4 electrovaccination, with available histological data and a minimum follow up of minimum 1 year, were retrospectively selected. Bone invasion was detected on imaging and/or histology. Median survival time of dogs with evidence of bone invasion (group 1) was 397 days and significantly shorter compared with dogs with oral melanomas not invading the bone (group 2, 1063 days). Dogs with tumours localised at the level of the cheek, lip, tongue and soft palate (soft tissue - group 3) lived significantly longer compared with dogs having tumours within the gingiva of the maxilla or mandible (hard tissue - group 4) with a median survival time of 1063 and 470 days, respectively. Within group 4, the subgroup of dogs with tumours not invading the bone (group 5) showed a significant prolonged survival time (972 days) in comparison with dogs of group 1 (bone invasion group). Similar results were obtained for the disease-free intervals amongst the different groups. Statistical analysis showed that Ki67 and mitotic count were correlated with shorter survival in patients of group 1 (with bone invasion). Bone invasion should always be assessed since it appears to be a negative prognostic factor.

Canine and feline uveal melanocytic tumours: Histologic and immunohistochemical characteristics of 32 cases

Objective

Gross, histopathological, and immunohistochemical characteristics of uveal melanocytic neoplasms in dogs and cats were investigated.

Samples

Thirty‐two enucleated globes with uveal melanocytic neoplasms, 27 from dogs and 5 from cats, were examined.

Procedures

Morphological characteristics of uveal melanocytic neoplasms in dogs and cats were evaluated with anti‐PNL2, anti‐Melan‐A, anti‐Ki‐67, anti‐caspase‐3, and anti‐BAP1 immunomarkers. Statistical analysis was performed to compare canine melanocytomas and melanomas.

Results

The 32 uveal neoplasms were classified as melanocytomas (19/27 in dogs) or melanomas (8/27 in dogs, 5/5 in cats). Most tumours (84%) were located in the anterior uvea. Neoplastic cells were classified as epithelioid, spindle‐shaped, mixed, or special type (balloon and signet ring cells). The percentage of cells with melanin, melanin concentration within cells, anisocytosis and anisokaryosis, mitotic count, lymphocytic inflammation, necrosis, vascular invasion, and glaucoma were also characterized. Anisocytosis, percentage of neoplastic cells with melanin, mitotic count, and indices (proliferation and apoptotic) varied significantly between canine uveal melanomas and melanocytomas; in general, melanomas had greater cell variability, were less pigmented, and had a higher mitotic count. The melanocytic origin of the neoplasms was confirmed by positive anti‐PNL2 immunolabelling (29/32) and positive anti‐Melan‐A immunolabelling (3/32). In canine uveal melanomas, anisocytosis and anisokaryosis correlated with less pigmentation and minimal pigmentation correlated with a high percentage of immunolabelling for caspase‐3.

Conclusions

Uveal melanocytomas were more common in dogs, and uveal melanomas were more frequent in cats. Anisocytosis, percentage of neoplastic cells with melanin, and mitotic count are important histologic characteristics of malignancy to evaluate in uveal melanocytic neoplasms. The proliferation and apoptotic indices are relevant when comparing malignant tumours with benign tumours.

Molecular Genetic Investigation of Digital Melanoma in Dogs

Canine digital melanoma, in contrast to canine oral melanoma, is still largely unexplored at the molecular genetic level. The aim of this study was to detect mutant genes in digital melanoma. Paraffin-embedded samples from 86 canine digital melanomas were examined for the BRAF V595E variant by digital droplet PCR (ddPCR), and for exon 11 mutations in c-kit. Furthermore, exons 2 and 3 of KRAS and NRAS were analysed by Sanger sequencing. Copy number variations (CNV) of KITLG in genomic DNA were analysed from nine dogs. The BRAF V595E variant was absent and in c-kit, a single nucleotide polymorphism was found in 16/70 tumours (23%). The number of copies of KITLG varied between 4 and 6. KRAS exon 2 codons 12 and 13 were mutated in 22/86 (25.6%) of the melanomas examined. Other mutually exclusive RAS mutations were found within the hotspot loci, i.e., KRAS exon 3 codon 61: 2/55 (3.6%); NRAS exon 2 codons 12 and 13: 2/83 (2.4%); and NRAS exon 3 codon 61: 9/86 (10.5%). However, no correlation could be established between histological malignancy criteria, survival times and the presence of RAS mutations. In summary, canine digital melanoma differs from molecular genetic data of canine oral melanoma and human melanoma, especially regarding the proportion of RAS mutations.

Multimodal Treatment of a Canine Lingual Melanoma Using a Combination of Immunotherapy and a Tyrosine Kinase Inhibitors

A 9-year-old female neutered Miniature Schnauzer was diagnosed with a lingual malignant melanoma on the basis of incisional biopsy and histopathology. The patient was initially given a guarded prognosis of a few months’ survival as surgical treatment options were declined by the owner. In order to control the disease a combination treatment of immunotherapy and tyrosine kinase inhibitors was initiated. The mass showed a marked and sustained reduction in size, whilst preserving quality of life for the patient, with a survival at the time of writing of 15 months since diagnosis. This experience suggests that combination therapy for oral malignant melanoma using immunotherapy and tyrosine kinase inhibitors may be successful in some patients and warrants further investigation.

Curative Intent Surgery of Oral Malignant Melanoma and Regional Lymph Node Biopsy Assessment in 25 Dogs: 2006-2017

Medical records were searched for dogs that had received curative intent surgery for oral malignant melanoma and ipsilateral excisional regional lymph node biopsy. Twenty-seven dogs were operated on and 25 dogs of these dogs met the inclusion criteria of signalment, post-excision margin status, presence of metastasis for each biopsied lymphocentrum, survival time post-excision, presence of recurrence or metastasis at follow-up or at death/euthanasia, location of the primary tumor, and any postoperative adjuvant treatment. These 25 dogs had complete tumor excision with tumor-free margins and 19 (76%) had postoperative adjuvant therapy. Median survival time after excision for the dogs in this study was 335.5 days. Results of this study support previous work that documents prolonged survival time following complete excision of oral malignant melanoma with tumor-free surgical margins in dogs. Additionally, 4 dogs (16%) had histologically confirmed regional lymph node metastasis at the time of definitive surgery.

Prognostic Value of Intratumoral Collagen Quantification in Canine Oral Melanomas

The majority of the melanocytic neoplasms are considered malignant and highly metastatic. However, a subset of the melanocytic tumors has a more favorable prognosis and the identification of precise prognostic markers for this neoplasm may be useful to guide treatment. The collagen architecture and density have been shown to correlate with tumor progression in human breast cancer and canine mast cell tumors. The purpose of the present study was to investigate the prognostic value of the intratumoral collagen index (ICI) as an indicator of postsurgical survival and its relation with other prognostic markers for canine oral melanomas (OMs). Twenty-two cases were tested for intratumoral collagen density using Masson's trichrome stain and morphometry. No differences were found between dogs regarding survival. The ICI was not correlated with proliferative activity or nuclear atypia. The results presented herein indicate that the quantity of intratumoral collagen in canine OMs is not an efficient indicator of postsurgical survival. Complementary studies about the expression and activity of enzymes that are capable of degrading extracellular matrix (ECM) components are necessary.

Molecular and Immunohistochemical Expression of LTA4H and FXR1 in Canine Oral Melanoma

Oral melanoma is a common canine tumor whose prognosis is considered ominous, but poorly predicted by histology alone. In the present study the gene and protein expression of Leukotriene A4 hydrolase (LTA4H) and Fragile-X-mental retardation-related protein1 (FXR1), both reported as related to metastatic potential in different tumors, were investigated in canine oral melanoma. The main aim of the study was to confirm and quantify the presence of LTA4H and FXR1 genes and protein in oral melanomas. A secondary aim was to investigate their association with histologic prognostic criteria (mitotic count, Ki-67 index). Formalin-fixed-paraffin-embedded canine oral melanomas (36) were collected and histopathological evaluation carried out. Immunolabelling for LTA4H and FXR1 and Ki-67 were performed. RT-PCR evaluated LTA4H and FXR1 gene expressions. Histologically, most tumors were epithelioid cell melanomas (19/36) and were amelanotic, mildly or moderately pigmented (5, 12 and 13/36 respectively), only 6 were highly pigmented. Mitotic count ranged 1-106, Ki-67 index ranged 4.5–52.3. Thirty-two (32/32) melanomas immunolabelled for LTA4H and 33/34 for FXR1. RT-PCR values ranged 0.76–5.11 ΔCt for LTA4H and 0.22–6.24 ΔCt for FXR1. Molecular and immunohistochemical expression of both LTA4H and FXR1 did not statically correlate with mitotic count or Ki-67 index. The present study demonstrates LTA4H and FXR1 gene and protein in canine oral melanoma, however their expression is apparently unrelated to histopathologic prognostic criteria. Although LTA4H and FXR1 seem unrelated to tumor behavior, their extensive expression in the present cohort of cases suggest that they may play a role in canine oral melanoma oncogenesis.

Endometrial Disease in Six Cats with Clinical and Histopathological Features Resembling Atypical Endometrial Hyperplasia in Humans

In humans, atypical endometrial hyperplasia (AEH) is considered as a precancerous lesion of endometrial adenocarcinoma (EA), from which it must be distinguished. Precancerous lesions have not been reported in cats with EA. We now document the histopathological features of endometrial lesions in six cats, which histopathologically resembled human AEH and had a good prognosis following ovariohysterectomy. Grossly, one cat presented with papillomatous nodules and three cats had pyometra. Histopathologically, proliferation of endometrial epithelial cells without atypia was observed in all cases. In some regions of the endometrium, cells had increased atypia and were arranged in stratified layers, which formed irregular ducts and papillary structures. No invasive behaviour or vascular invasion was observed. On the basis of these findings, the cats were diagnosed with non-invasive or early-stage adenocarcinoma. Immunohistochemistry for oestrogen receptor and progesterone receptor revealed an inverse correlation with the severity of the endometrial lesions and degree of malignancy of tumour cells. Ki67 labelling revealed that mitotic activity increased as the lesion developed. All cats survived, with a median survival time of 385 days (range: 229-744 days). The distribution of the histopathological endometrial changes and the non-invasive behaviour in these feline cases resemble cases of AEH in humans.

Difference in outcome between curative intent vs marginal excision as a first treatment in dogs with oral malignant melanoma and the impact of adjuvant CSPG4-DNA electrovaccination: A retrospective study on 155 cases

Canine oral malignant melanoma is locally invasive and highly metastatic. At present, the best option for local control is en bloc excision followed by radiation if excision margins are incomplete. Adjuvantly, the role of chemotherapy is dubious while immunotherapy appears encouraging. This retrospective study evaluated 155 dogs with oral malignant melanomas (24 stage I, 54 stage II, 66 stage III and 11 stage IV) managed in a single institution. The aim was to evaluate the differences in median survival time (MST) and disease-free interval (DFI) between dogs which, at presentation, were treated surgically with a curative intent (group 1) vs those marginally excised only (group 2). MST in group 1 was longer than in group 2 (594 vs 458 days), but no significant difference was found (P = .57); a statistical difference was, however, found for DFI (232 vs 183 days, P = .008). In the subpopulation of vaccinated dogs, the impact of adjuvant anti-CSPG4 DNA electrovaccination was then evaluated (curative intent, group 3, vs marginal, group 4); a significant difference for both MST (1333 vs 470 days, respectively, P = .03) and DFI (324 vs 184 days, respectively, P = .008) was found. Progressive disease was significantly more common in dogs undergoing marginal excision than curative intent excision for both the overall population (P = .03) and the vaccinated dogs (P = .02). This study pointed out that, after staging, wide excision together with adjuvant immunotherapy was an effective approach for canine oral malignant melanoma.

Comparative Review of Malignant Melanoma and Histologically Well-Differentiated Melanocytic Neoplasm in the Oral Cavity of Dogs

Oral malignant melanoma (OMM) is the most common neoplasm of the canine oral cavity. It is characterized by its aggressive local disease as well as its high rate of lymphatic invasion and distant metastasis. OMM carries a poor prognosis, with most patients succumbing to the disease due to progression of the neoplasm. Histopathologically, OMM is characterized by significant nuclear atypia, a mitotic index of greater than 4/10 hpf, and evidence of vascular invasion or metastasis. Clinically, these lesions can become locally invasive, causing lysis of bones and severe inflammation of the surrounding soft tissue. With time, these lesions can spread to the regional lymph node and to the lungs and other organs. Prognosis can vary depending on the size of the primary tumor, regional node involvement, and distant metastatic disease; however, multiple studies report a relatively short median survival time ranging from less than 4 months to 8 months. Histologically well- differentiated melanocytic neoplasms (HWDMN) are a variant of OMM and sometimes referred to as canine oral melanocytic neoplasms of low malignant potential. Unlike OMM, patients with HWDMN have longer survival times. Histopathologically, HWDMNs have well-differentiated melanocytes with a low mitotic index of 3 or less per 10 hpf and minimal nuclear atypia. HWDMNs have better prognosis with a mean survival time of up to 34 months. This article is a comparative review of OMM and its less aggressive counterpart.

Three neoplasms in a Eurasian otter (Lutra lutra): malignant melanoma, trichoblastoma and mammary gland adenoma

An eighteen-year-old female Eurasian otter became emaciated and died. Necropsy examination revealed nose and thoracic cutaneous masses, abdominal subcutaneous mass, and multiple nodules in the liver and lungs. Malignant melanoma was found in the nose cutaneous mass and to have metastasized to the liver, lungs, kidneys, adrenal glands, mammary glands and left mandibular lymph node. The neoplastic cells were labeled for vimentin, melanoma, and S100. The cutaneous mass in the thoracic area consisted of spindle shaped neoplastic epithelial cells and was diagnosed as trichoblastoma. Mammary gland adenoma was observed in the abdominal subcutaneous mass. This is the first report of primary three neoplasms of malignant melanoma, trichoblastoma and mammary gland adenoma in a Eurasian otter.

Tumor-infiltrating lymphocytes (TILs) in feline melanocytic tumors: A preliminary investigation

The presence and the role of tumor-infiltrating lymphocytes (TILs) in different types of tumors, but particularly in melanoma, has become more and more investigated during the last decade, both in human and veterinary medicine. Melanocytic tumors are quite rare in cats, with diffuse iris melanoma being the most commonly diagnosed in this species. The aim of this study was to characterize the lymphocytic infiltration in feline melanocytic tumors and to analyze their association with the histological features of malignancy recognized in these tumors, as well as with the expression of the most commonly used immunohistochemical markers. Thirty-eight feline melanocytic tumors were retrospectively selected; histological and immunohistochemical characterization of the tumors (histologic criteria of malignancy; S100, Melan A, and PNL2 expression) and of TILs (presence/absence, density, distribution, and grade; CD3, CD20 expression) were performed and associations between them tested. Results showed that TILs grade increased with cellular pleomorphism (P < 0.05) and, within the group of cutaneous melanocytic tumors, also with the mitotic count (P < 0.05). On the other hand, TILs grade was inversely associated with the percentage of neoplastic cells positive for Melan A (P < 0.05) and PNL2 (P < 0.05). Both CD3⁺ and CD20⁺ lymphocytes increased significantly with TILs grade and in association with mitotic count, when stratified in low/high quantity. This preliminary study suggests that TILs in feline melanoma may be associated with histologic features of malignancy and loss of melanocytic-specific markers, such as Melan A and PNL2. Further studies, with a larger cohort and follow-up information, are recommended.

COX-2 Silencing in Canine Malignant Melanoma Inhibits Malignant Behaviour

Metastatic melanoma is a very aggressive form of cancer in both humans and dogs. Dogs primarily develop oral melanoma of mucosal origin. Although oral melanoma in humans is rare, both diseases are highly aggressive with frequent metastases. This disease represents a “One Health” opportunity to improve molecular and mechanistic understanding of melanoma progression. Accumulating evidence suggests that cyclooxygenase-2 (COX-2) may play a critical role in the malignant behaviour of melanoma. In this study we analysed 85 histologically confirmed melanomas from canine patients and showed that COX-2 is overexpressed in both oral and cutaneous melanomas and that COX-2 expression correlates with established markers of poor prognosis. To determine the role of COX-2 in melanoma we developed two melanoma cell lines with stable integration of an inducible doxycycline-regulated expression vector containing a COX-2 targeted micro-RNA (miRNA). Using this system, we showed that cellular proliferation, migration and invasion are COX-2 dependent, establishing a direct relationship between COX-2 expression and malignant behaviour in canine melanoma. We have also developed a powerful molecular tool to aid further dissection of the mechanisms by which COX-2 regulates melanoma progression.

Quantification of Global DNA Methylation in Canine Melanotic and Amelanotic Oral Mucosal Melanomas and Peripheral Blood Leukocytes From the Same Patients With OMM: First Study

Oral mucosal melanomas (OMMs) are aggressive and resistant cancers of high importance in veterinary oncology. Amelanotic OMM produces comparatively less melanin and is considered to be more aggressive than melanotic OMM. Global DNA methylation profiles with hypomethylated or hypermethylated patterns have both been associated with aggressive neoplasms; however, global DNA hypomethylation seems to correlate to higher aggressiveness. Accordingly, global DNA methylation in peripheral blood leukocytes has been investigated to understand the role of systemic or environmental factors in cancer development. This study aimed to quantify global DNA methylation in canine melanotic and amelanotic OMM samples and in the peripheral blood leukocytes of the same dogs. Tumor tissue samples were collected from 38 dogs, of which 19 were melanotic and 19 were amelanotic OMM. These were submitted to immunohistochemistry (IHC) with anti-5-methylcytosine (5mC) and anti-Ki67 primary antibodies. Ki67- and 5mC-positive nuclei were manually scored with the help of an image analysis system. Peripheral blood samples were collected from 18 among the 38 OMM-bearing dogs and from 7 additional healthy control dogs. Peripheral blood leukocytes were isolated from the 25 dogs, and DNA was extracted and analyzed by high-performance liquid chromatography (HPLC) for global DNA methylation. The pattern of global DNA methylation in both canine melanotic and amelanotic OMM indicated higher percentages of weakly or negatively stained nuclei in most of the OMM cells, presuming predominant global DNA hypomethylation. In addition, Ki67 counts in amelanotic OMM were significantly higher than those in melanotic OMM (p < 0.001). Global DNA methylation different immunostaining patterns (strong, weak or negative) correlated with Ki67 scores. Global DNA methylation in circulating leukocytes did not differ between the 9 melanotic and 9 amelanotic OMM or between the 18 OMM-bearing dogs and the 7 healthy dogs. This study provides new information on canine melanotic and amelanotic OMM based on global DNA methylation and cell proliferation.

H2AFZ: A Novel Prognostic Marker in Canine Melanoma and a Predictive Marker for Resistance to CDK4/6 Inhibitor Treatment

Uncontrolled proliferation is a key feature of tumor progression and malignancy. This suggests that cell-cycle related factors could be exploited as cancer biomarkers and that pathways specifically involved in the cell cycle, such as the Rb-E2F pathway, could be targeted as an effective anti-tumor therapy. We investigated 34 formalin-fixed paraffin-embedded (FFPE) tissue samples of canine cutaneous melanocytoma, cutaneous melanoma, and oral melanoma. Corresponding clinical follow-up data were used to determine the prognostic value of the mRNA expression levels of several cell cycle regulated E2F target genes (E2F1, DHFR, CDC6, ATAD2, MCM2, H2AFZ, GINS2, and survivin/BIRC5). Moreover, using four canine melanoma cell lines, we explored the possibility of blocking the Rb-E2F pathway by using a CDK4/6 inhibitor (Palbociclib) as a potential anti-cancer therapy. We investigated the expression levels of the same E2F target gene transcripts before and after treatment to determine the potential utility of these molecules as predictive markers. The E2F target gene H2AFZ was expressed in 91.43% of the primary tumors and H2AFZ expression was significantly higher in cases with unfavorable clinical outcome. Among the other tested genes, survivin/BIRC5 showed as well-promising results as a prognostic marker in canine melanoma. Three of the four tested melanoma cell lines were sensitive to the CDK4/6 inhibitor. The resistant cell line displayed higher expression levels of H2AFZ before treatment compared to the CDK4/6 inhibitor-sensitive cell lines. The present results suggest that CDK4/6 inhibitors could potentially be used as a new anti-cancer treatment for canine melanoma and that H2AFZ could serve as a prognostic and predictive marker for patient selection.

Quantitative Expression of TYR, CD34, and CALD1 Discriminates Between Canine Oral Malignant Melanomas and Soft Tissue Sarcomas

Canine oral malignant melanomas (OMMs) exhibit a variety of morphologic phenotypes, including a spindloid variant. The microscopic diagnosis of spindloid OMMs is based on junctional activity and/or the presence of melanin pigment. In the absence of these features, spindloid OMMs are difficult to differentiate from soft tissue sarcomas (STS). An antibody cocktail (MDX) that includes Melan-A, PNL2, and tyrosinase-related proteins 1 and 2 (TRP-1 and TRP-2) is the current gold standard for identifying amelanotic OMMs by immunohistochemistry (IHC). However, MDX is less sensitive for diagnosing spindloid amelanotic OMMs. This raises concern for biopsy specimens that lack overlying epithelium, making it potentially difficult to differentiate OMM from STS by IHC. The goal of this study was to identify additional markers to help differentiate between STS and OMMs that lack pigment and junctional activity. SOX-10 has recently been proposed as a sensitive marker for melanocytes in humans but has not been validated in dogs. Similarly, RNA expression for various genes has been analyzed in humans, but not in the context of diagnosing canine melanocytic neoplasms. For this retrospective study, formalin-fixed, paraffin-embedded tissues from 20 OMMs, 20 STS, and 20 oral spindle cell tumors (OSCTs) that lacked junctional activity and pigmentation were selected. IHC for MDX, SOX-10, and laminin, in parallel with RT-qPCR of TYR, SOX10, CALD1, CD34, DES, and LAMA1, was performed in all cases. TYR, CD34, and CALD1 were the most discriminatory genes in differentiating between OMM and STS, all having 100% specificity and 65, 95, and 60% sensitivity, respectively. While all 20 OMMs were immunohistochemically labeled for SOX-10, two STS were also labeled (100% sensitivity and 90% specificity). MDX IHC labeled all 20 OMMs and no STS. Surprisingly, none of the 20 OSCTs expressed TYR RNA above the cutoff, and 14/20 OSCTs expressed CALD1 or CD34 RNA above the cutoff, thereby confirming them as STS. Four OSCT were suspect STS, and no OSCTs were confirmed as OMMs based on IHC and RNA expression patterns. In conclusion, the RNA levels of TYR, CD34, and CALD1 should be evaluated in suspected amelanotic OMMs that are negative for MDX to accurately differentiate between OMM and STS.

Metastatic melanoma in a Saanen goat: clinical, ultrasonographic and anatomopathological aspects - case report

ABSTRACT This report describes clinical, ultrasonographic and anatomopathological findings in a case of metastatic melanoma in an adult Saanen goat. Clinically, the goat had apathy, an intra-abdominal palpable firm structure, and exophytic keratinized areas on the skin of the udder. Ultrasound revealed non-encapsulated oval structures, with heterogeneous echogenicity and marked central and peripheral vascularization, and hypoechoic hepatic multifocal to coalescent areas. In the udder, there were non-encapsulated oval structures with heterogeneous echogenicity and hyperechoic center surrounded by hypoechogenic tissue. Grossly, there were black multifocal to coalescent areas in the liver, as well as black nodules in mammary and mesenteric lymph nodes, uterus, spleen, and myocardium. Microscopically, multifocal melanocytic neoplastic proliferation was observed in the dermis and junction of the udder epidermis. Most of the neoplastic cells had cytoplasmic granules of melanin. In the liver there were areas of neoplastic tissue compressing the adjacent parenchyma, with central foci of necrosis, mild desmoplasia, and multifocal infiltration of malignant cells into the adjacent tissues. Similar findings were observed in the mammary and mesenteric lymph nodes, uterus, spleen, and myocardium, which characterized metastatic melanoma. Ultrasonography played a key role for establishing the diagnosis of a metastatic melanoma and helped establish a proper clinical management protocol.

Gross, histologic, and immunohistochemical characteristics of cutaneous chromatophoromas in captive bearded dragons

Chromatophoromas are neoplasms that develop from the dermal pigment-bearing and light-reflecting cells (chromatophores) in the skin of reptiles, fish, and amphibians. Seventeen cutaneous chromatophoromas were identified from 851 bearded dragon submissions (2%) to a private diagnostic laboratory in a 15-y period. No sex predilection was found. Ages ranged from 9 mo to 11 y. Chromatophoromas most commonly were single, raised, variably pigmented masses or pigmented scales on the trunk, and less commonly the extremities or head. Microscopically, iridophoromas, melanophoromas, mixed chromatophoromas, and nonpigmented chromatophoromas were identified. Neoplasms were often ulcerated and invaded deep into the subcutis and muscle. Most commonly, nuclear atypia was mild-to-moderate, and mitotic count was low. Six neoplasms had abundant, periodic acid-Schiff-positive, mucinous stroma. Histologic examination was often adequate to diagnose chromatophoromas in bearded dragons given that 11 of 17 had some degree of pigmentation, although it was often scant. IHC for S100 and PNL2 could be helpful to diagnose poorly pigmented neoplasms. No lymphatic invasion or metastases at the time of excision were noted in any of the cases. Follow-up data were available for 6 cases, with no reports of recurrence or neoplasia-related death. Two cases had elevated mitotic counts and nuclear pleomorphism, which has been associated with metastasis in other reports of bearded dragon chromatophoromas. In general, it appears that aggressive surgical excision is often curative, but monitoring may be warranted for cases in which tumors had high mitotic count and nuclear pleomorphism.

Immunohistochemical evaluation of suspected oral malignant melanoma in cats

Oral malignant melanoma (OMM) is considered the third most common oral malignant neoplasm in cats, but its variable morphology and frequent lack of melanin pigment make it a diagnostic challenge. Twenty-two cases of cats with malignant oral neoplasms that were diagnosed as OMM or listed OMM as a suspected differential diagnosis on the biopsy report were examined using an immunohistochemistry (IHC) panel for S100, melan-A, PNL2, laminin, CD34, and pan-cytokeratin. Although OMM was suspected (n = 14) or previously diagnosed (n = 8), only 2 cases were immunohistochemically confirmed as OMM. Seven cases were classified as soft tissue sarcoma based on positive expression of CD34 or laminin, and one was classified as carcinoma based on positive expression of pan-cytokeratin. The majority of cases (n = 12) were categorized as unclassified malignant neoplasms because they did not express melan-A, PNL2, laminin, CD34, or pan-cytokeratin; however, a proportion of these did express S100 (n = 7). Long-term prognosis of all 22 cats was poor, with a median survival time of 87 days (range = 2-249 days). Cases with longer survival times (>100 days) were treated with surgery, radiation therapy, or a combination. For feline oral malignant neoplasms thought to be OMM, routine use of IHC is required for an accurate diagnosis.

PD-1, PD-L1, and PD-L2 Gene Expression and Tumor Infiltrating Lymphocytes in Canine Melanoma

Melanoma in humans and dogs is considered highly immunogenic; however, the function of tumor-infiltrating lymphocytes (TILs) is often suppressed in the tumor microenvironment. In humans, current immunotherapies target checkpoint molecules (such as PD-L1, expressed by tumor cells), inhibiting their suppressive effect over TILs. The role of PD-L2, an alternative PD-1 ligand also overexpressed in malignant tumors and in patients with anti-PD-L1 resistance, remains poorly understood. In the current study, we evaluated the expression of checkpoint molecule mRNAs in canine melanoma and TILs. Analysis of checkpoint molecule gene expression was performed by RT-qPCR (real-time quantitative polymerase chain reaction) using total RNA isolated from formalin-fixed and paraffin-embedded melanomas (n = 22) and melanocytomas (n = 9) from the Virginia Tech Animal Laboratory Services archives. Analysis of checkpoint molecule expression revealed significantly higher levels of PDCD1 (PD-1) and CD274 (PD-L1) mRNAs and an upward trend in PDCD1LG2 (PD-L2) mRNA in melanomas relative to melanocytomas. Immunohistochemistry revealed markedly increased numbers of CD3⁺ T cells in the highest PD-1-expressing subgroup of melanomas compared to the lowest PD-1 expressors, whereas densities of IBA1⁺ cells (macrophages) were similar in both groups. CD79a⁺ cell numbers were low for both groups. As in human melanoma, overexpression of the PD-1/PD-L1/PD-L2 axis is a common feature of canine melanoma. High expression of PD-1 and PD-L1 correlates with increased numbers of CD3⁺ cells. Additionally, the high level of IBA1⁺ cells in melanomas with low PD-1 expression and low CD3⁺ cells levels suggest that the expression of checkpoint molecules is modulated by interactions between T cells and cancer cells rather than histiocytes.

Evaluation of prognostic impact of pre-treatment neutrophil to lymphocyte and lymphocyte to monocyte ratios in dogs with oral malignant melanoma treated with surgery and adjuvant CSPG4-antigen electrovaccination: an explorative study

The role of systemic inflammation in cancer's progression has been widely investigated, especially in melanoma in humans. Pre-treatment leukocyte counts and ratios play a recognized prognostic role in several types of malignancies, but no information is available regarding canine oral malignant melanoma (COMM). The purpose of this explorative retrospective study was to investigate the prognostic impact of pre-treatment neutrophil to lymphocyte (NLR) and lymphocyte to monocyte (LMR) ratios in dogs with oral malignant melanoma that underwent surgical resection and immunotherapy with adjuvant CSPG4-antigen electrovaccination. Thirty-nine dogs with histologically confirmed oral melanoma and with available pre-treatment haematological analyses, performed at maximum 60 days before the first treatment, were retrospectively enrolled. Statistical analysis was performed to explore possible correlations among NLR and LMR with age, clinical stage, tumour pigmentation, tumour size, nuclear atypia, mitotic index, Ki67, CSPG4 expression, ulceration, bone invasion and excision margins status. The impact of NLR and LMR on overall survival time (OST) was explored among various ratio cut off and across different time points with Kaplan-Meier method. No significant relationship was identified between leukocytes ratios and histological parameters, CSPG4 expression, excision margin status, age, tumour size and clinical stage. NLR and LMR did not display a prognostic impact on the survival time of the entire population. Pre-treatment leukocyte ratios may not represent a useful prognostic factor in dogs with oral melanoma, especially in absence of distant metastatic disease.

Immunohistochemical expression and prognostic significance of MAGE-A in canine oral malignant melanoma

Canine oral malignant melanoma (COMM) is considered a chemo-resistant cancer with a poor long-term prognosis. The melanoma-associated antigen A (MAGE-A) genes, which belong to the cancer-testis antigen family, are expressed in several different canine cancers but not in normal somatic tissue. This study evaluates the expression of MAGE-A proteins and their prognostic role in COMM. The study was conducted in 2 parts. During the first part, biopsies from oral malignant melanomas from 43 dogs were examined and immunohistochemically assessed for expression of MAGE-A proteins. For the second part, the association between MAGE-A expression and outcome was assessed using follow-up data which was available for 20 dogs whose primary tumour had been controlled with surgery +/- radiation therapy. MAGE-A proteins were expressed in 88.4% (38/43) of oral malignant melanomas and had a predominantly cytoplasmic expression pattern. Immunopositivity was observed in more than 50% of the cells in 21 dogs (48.8%). Immunostaining intensity was classified as weak, moderate and intense in 16 (37%), 16 (37%) and 6 (14%) cases, respectively. No staining for MAGE-A was seen in 5 dogs (11%). Dogs whose COMM had weak MAGE-A staining intensity had a median survival time (MST) of 320 days while this was 129 days for dogs with moderate and intense immunostaining (p = 0.161). Dogs whose COMM had >50% of positive staining neoplastic cells had an MST of 141 days and dogs with a staining <50% had an MST of 320 days (p = 0.164). MAGE-A expression did not influence survival in our cohort.

Correlation Between KIT Expression and c-Kit Mutations in 2 Subtypes of Canine Oral Melanocytic Neoplasms

c-Kit mutations have been reported in 15% to 40% of certain human melanoma subtypes, including those histologically similar to canine oral malignant melanomas. Therapeutic response to tyrosine kinase inhibitors has been demonstrated in those human patients. As canine oral malignant melanomas tend to have a poor prognosis despite aggressive surgical removal, evaluation of KIT expression and identification of c-Kit mutations in canine oral melanocytic neoplasms was performed to determine if there is any indication that tyrosine kinase inhibitor drugs might effectively treat any of these cases. This study evaluated 27 canine oral malignant melanomas and 12 canine histologically well-differentiated oral melanocytic neoplasms for activating c-Kit mutations, determined differences in immunohistochemical expression of KIT and c-Kit mutation status, and determined if KIT expression could predict c-Kit mutation status. Among samples that contained intraepithelial nests of neoplastic melanocytes in the KIT-labeled sections, KIT was expressed within cells in these nests in 22/23 (96%) malignant melanomas and 5/7 histologically well-differentiated neoplasms. KIT was expressed in 10% to 30% of neoplastic melanocytes in the lamina propria in 3/24 (13%) malignant melanomas, but 0/9 (0%) histologically well-differentiated neoplasms. Next-generation sequencing identified 85 variants in c-Kit, including 9 nonsynonymous mutations that resulted in amino acid changes predicted to affect protein function. c-Kit mutations with predicted deleterious protein effects were more common in malignant melanomas (8/27 [30%] vs 1/12 [8%]). There was no apparent relationship between detected c-Kit mutations and KIT expression. These results do not support the use of therapies that target c-Kit.

JARID1-targeted histone H3 demethylase inhibitors exhibit anti-proliferative activity and overcome cisplatin resistance in canine oral melanoma cell lines

Histone demethylases are overexpressed or display altered activity in numerous human cancers leading to alterations in cell cycle dynamics, DNA repair kinetics, and therapeutic resistance. Consequently, therapeutic targeting of histone demethylases has become an active and promising area of research in human oncology. However, the role of histone demethylases and the potential efficacy of demethylase inhibition in canine cancers remains largely unknown. In the present work, we addressed this knowledge gap by exploring the therapeutic potential of histone demethylase inhibitors (HDIs) in canine oral melanoma. Using canine melanoma cell lines, we determined that broad spectrum HDIs result in decreased cell survival and prolonged DNA damage repair kinetics. We then showed that JARID1B, a histone H3 demethylase implicated in proliferation-dormancy regulation and drug sensitivity in human cancers, is highly expressed in canine tumour tissues. HDIs targeting JARID1B, and related JARID1 family members, significantly reduced survival fractions in canine melanoma cell lines, but did not appear to modulate DNA damage repair kinetics like broad spectrum HDI treatments. Importantly, we found that the anti-proliferative effects of JARID1-targeted HDIs are preserved in cell lines resistant to platinum-based chemotherapeutics, suggesting that HDIs may serve as a viable therapeutic strategy when faced with oral melanomas that progress despite the use of conventional therapies.

Characterization of Primary Cultures of Normal and Neoplastic Canine Melanocytes

Simple Summary

Melanoma is one of the most aggressive cancers in humans, with high rates of metastasis and a poor prognosis. Because of its environmental, biological and genetic features, numerous studies indicate the dog as a good comparative model for human melanoma. Primary cell cultures of healthy and neoplastic melanocytes derived from skin and oral mucosa of dogs with spontaneous tumors are established in this study. This model could represent a suitable tool to compare biological and molecular features of normal and neoplastic melanocytes from the same patient, to investigate the pathways underlying the oncogenic transformation, and to apply a more personalized therapeutic strategy. The cell cultures also meet international guidelines that encourage the use of alternative models to animal ones for the study of oncological diseases.

Abstract

Although numerous animal models, especially mouse models, have been established for the study of melanoma, they often fail to accurately describe the mechanisms of human disease because of their anatomic, physiological, and immune differences. The dog, as a spontaneous model of melanoma, is nowadays considered one of the most valid alternatives due to the heterogeneity of clinical presentations and of histological and genetic similarities of canine melanoma with the human counterpart. The aim of the study was to optimize a protocol for the isolation and cultivation of healthy and neoplastic canine melanocytes derived from the same animal and obtained from cutaneous and mucosal (oral) sites. We obtained five primary tumor cell cultures (from 2 cutaneous melanoma, 2 mucosal melanoma and 1 lymph node metastasis) and primary normal melanocyte cell cultures (from normal skin and mucosa) from the same dogs. Immunocytochemical characterization with Melan A, PNL2 and S100 antibodies confirmed the melanocytic origin of the cells. This work contributes to expanding the case record of studies on canine melanoma cell cultures as suitable model to study human and canine melanoma. To the authors’ knowledge, this is the first report of isolation of normal skin and mucosal canine melanocytes.

The role of COX expression in the prognostication of overall survival of canine and feline cancer: A systematic review

Cyclooxygenase (COX) isoforms-1 and -2 have been extensively investigated in cancer. Although COX-2 is the isoform most studied and has been described in several malignancies associated with histologic criteria of malignancy and worse prognosis, COX-1 has also been linked to some forms of cancer. With the present review our aim was to summarize the current state of knowledge and clarify if and in which type of tumours COX-1 and/or COX-2 expression have real prognostic implications. We searched PubMed database for prognostic studies using predefined inclusion criteria in order to ascertain the prognostic value of COX-1 and COX-2 in malignant neoplasia in dogs and cats. Eighteen studies were analysed. COX-2 was shown to be a negative prognostic factor in canine and feline mammary tumours, canine mast cell tumour, canine melanoma, canine osteosarcoma and canine renal cell carcinoma. COX-1 showed a negative prognostic value in feline oral squamous cell carcinoma (SCC). We found high heterogeneity among studies regarding COX immunohistochemical evaluation methodology even in the same type of neoplasia pointing out the need for its standardization at least by tumour type. The available data support the use of COX-2 as a prognostic factor in canine (mammary carcinoma, mast cell tumour, melanoma, osteosarcoma and renal carcinoma) and feline (mammary carcinoma) cancers. For COX-1, its use is advised in feline oral SCC.

Mast Cell Tumors and Histiocytomas in Domestic Goats and Diagnostic Utility of CD117/c-Kit and Iba1 Immunohistochemistry

Cutaneous round cell tumors in goats present a diagnostic challenge. In this article, we provide a description of caprine cutaneous mast cell tumors (MCT) and histiocytomas, and report on the validation of anti-human antibodies to CD117/KIT and Iba1 by immunohistochemistry on a range of caprine tissues. Cells immunolabeled for CD117/KIT included resident mast cells in normal lung and skin, interstitial cells of Cajal (intestine), and neuronal cell bodies (brain). Cells immunolabeled for Iba1 included resident macrophages in many tissues including normal lung, dendritic cells (hemolymphatic tissues), Kupffer cells, and microglia. Of 5 cutaneous MCT, only one had metachromasia of cytoplasmic granules; however, neoplastic cells of all 5 MCT had positive immunolabeling for CD117/KIT. The CD117/KIT immunolabeling pattern was predominately focal paranuclear in 3 cases, and cytoplasmic or membranous in 1 case each. Two histiocytomas were identified and had strong positive immunolabeling for Iba1 but not CD117/KIT. All 7 cutaneous round cell tumors described herein occurred in goats less than 4 years of age; the 2 cutaneous histiocytomas were in goats less than 14 months of age. Neither of the cutaneous histiocytomas recurred within 24 months of surgical removal.

KIT Somatic Mutations and Immunohistochemical Expression in Canine Oral Melanoma

Simple Summary

Malignant melanomas arising from mucosal sites are very aggressive neoplastic entities which affect both humans and dogs. The family of tyrosine kinase receptors has been increasingly studied in humans for this type of neoplasm, especially the gene coding for the proto-oncogene KIT, and tyrosine kinase inhibitors are actually available as treatment. However, KIT alteration status in canine oral melanoma still lacks characterization. In this study, we investigated the mutational status and the tissue expression of KIT through DNA sequencing and immunohistochemical analysis, respectively. A homogeneous cohort of 14 canine oral melanomas has been collected, and while tissue expression of the protein was detected, no mutations were identifiable, most likely attributing the dysregulation of this oncogene to a more complex pattern of genomic aberration.

Abstract

Canine oral melanoma (COM) is an aggressive neoplasm with a low response to therapies, sharing similarities with human mucosal melanomas. In the latter, significant alterations of the proto-oncogene KIT have been shown, while in COMs only its exon 11 has been adequately investigated. In this study, 14 formalin-fixed, paraffin-embedded COMs were selected considering the following inclusion criteria: unequivocal diagnosis, presence of healthy tissue, and a known amplification status of the gene KIT (seven samples affected and seven non-affected by amplification). The DNA was extracted and KIT target exons 13, 17, and 18 were amplified by PCR and sequenced. Immunohistochemistry (IHC) for KIT and Ki67 was performed, and a quantitative index was calculated for each protein. PCR amplification and sequencing was successful in 97.62% of cases, and no single nucleotide polymorphism (SNP) was detected in any of the exons examined, similarly to exon 11 in other studies. The immunolabeling of KIT was positive in 84.6% of the samples with a mean value of 3.1 cells in positive cases, yet there was no correlation with aberration status. Our findings confirm the hypothesis that SNPs are not a frequent event in KIT activation in COMs, with the pathway activation relying mainly on amplification.

Melanoma oral amelanótico metastático com acometimento neurológico e gonadal em um cão fêmea ˗ relato de caso

RESUMO Relata-se um caso de melanoma oral disseminado em uma cadela de dois anos, com protrusão de bulbo ocular unilateral e quadro convulsivo progressivo. Os exames de imagem revelaram aumento de volume nas regiões submandibular, maxilar e cerebral, padrão nodular pulmonar e aumento das dimensões ovarianas. A citologia da massa submandibular indicou proliferação epitelial maligna, enquanto a biópsia excisional foi sugestiva de melanoma amelanótico. Na necropsia, havia uma massa gengival localmente infiltrativa e nodulações brancas nos linfonodos, nos rins, no pulmão, no cérebro e nos ovários, indicativas de metástase. O diagnóstico histopatológico consistiu de neoplasia maligna metastática indiferenciada, indicativo de melanoma amelanótico. Células caracterizadas por núcleo com cromatina espessa, múltiplos nucléolos bem evidentes, mitoses atípicas e multinucleações consistiram nos principais critérios de malignidade. No espaço peritrabecular ósseo facial, havia rara diferenciação pigmentar melanocítica, confirmada histoquimicamente pela técnica de Fontana-Massom e Giemsa. Algumas células foram positivas pela imuno-histoquímica para PNL-2 e Melan-A, e o diagnóstico de melanoma amelanótico disseminado foi firmado. A indiferenciação neoplásica marcante, com disseminação metastática multissistêmica e acometimento mútuo de sítios anatômicos pouco comuns, conjuntamente com a ampla variação dos padrões celulares, foi responsável pelo desafio diagnóstico do presente caso, ressaltando o papel decisivo da imuno-histoquímica para confirmação diagnóstica. A importância clínica deste trabalho consiste ainda em alertar a comunidade clínica e científica acerca da dificuldade diagnóstica, devendo-se considerar o melanoma amelanótico como diferencial mesmo em casos de lesões orais menos perceptíveis e/ou desprovidas de pigmentação.

Long interspersed nucleotide element-1 hypomethylation in canine malignant mucosal melanoma

Canine malignant melanoma is a common cancer with a high mortality rate and is a clinically important disease. DNA methylation has been considered to be a potential tumorigenic mechanism through aberrant DNA methylation at promoter region which represses gene transcription. Global hypomethylation could also facilitate chromosome instability. There are few reports regarding DNA methylation in canine malignant melanoma; therefore, the purpose of this study was to examine DNA methylation status of long interspersed nucleotide element-1 (LINE-1) to be a surrogate marker of genome-wide methylation changes in this disease. We measured levels of DNA methylation of two adjacent cytosine-guanine sites on CpG island (CGI) at the putative promoter of canine LINE-1 sequence by bisulphite-pyrosequencing in 41 canine melanoma patient samples as well as six cell lines compared with normal mucosae. The survival rates were obtained from owners or medical records. We found DNA methylation levels of LINE-1 in normal mucosae were methylated. Interestingly, both melanoma cell lines and clinical melanoma samples showed remarkable hypomethylation. In addition, patients with lower LINE-1 methylation showed worse prognosis than those with higher LINE-1 methylation, though the difference did not reach statistical significance (P = .09). Here, we demonstrate that hypomethylation of LINE-1 is an epigenetically aberrant feature in canine melanoma with possible prognostic value.