Nonocular Melanocytic Neoplasia in Cats: Characterization and Proposal of a Histologic Classification Scheme to More Accurately Predict Clinical Outcome

SOX-10 and TRP-1 expression in feline ocular and nonocular melanomas

In felines, ocular and nonocular melanomas are uncommon tumors that represent a diagnostic challenge for pathologists, especially when amelanotic. To date, the immunohistochemical diagnostic panel in cats is based on specific melanocytic markers (Melan-A and PNL2) and a nonspecific but sensitive marker (S100). In human medicine, SOX-10 is reported to be a sensitive antibody for the detection of melanoma micrometastasis in the lymph node. TRP-1, an enzyme involved in melanogenesis, has recently been used in humans and dogs as a specific melanocyte marker. The aim of this study was to evaluate the cross-reactivity and the expression of SOX-10 and TRP-1 antibodies in feline normal tissue and melanocytic tumors. Thirty-one cases of ocular, cutaneous, and oral melanomas were retrospectively evaluated and confirmed by histopathological examination and by immunolabeling with Melan-A and/or PNL2. SOX-10 nuclear expression in normal tissues was localized in epidermal, subepidermal, hair bulb, and iridal stromal melanocytes and dermal nerves. In melanomas, nuclear expression of SOX-10 was detected in ocular (11/12; 92%), oral (6/7; 86%), and cutaneous sites (12/12; 100%). TRP-1 cytoplasmic immunolabeling in normal tissue was observed in epidermal and bulbar melanocytes and in the lining pigmented epithelium of the iris and in its stroma. Its expression was positively correlated to the degree of pigmentation in the tumor and was observed in 75% of ocular (9/12), 43% of oral (3/7), and 33% of cutaneous melanomas (4/12). This study demonstrated the cross-reactivity of SOX-10 and TRP-1 antibodies in feline non-neoplastic melanocytes and their expression in ocular and nonocular melanomas.

Clinicopathologic description of a cutaneous melanocytic tumor in a 1-year-old cat

A feline cutaneous melanocytic tumor in a 1-year-old cat is reported. The cytologic, histologic, and immunohistochemical characteristics of the pediatric feline cutaneous melanocytoma are included. A solitary, black-colored nodule on the head was histologically diagnosed as the epithelioid type of melanocytoma. Immunohistochemically, the neoplastic melanocytes demonstrated immunoreactivity to the S100 and MelanA antibodies but not to the PNL2 antibody. Despite high mitotic counts (17/10HPFs) and a Ki67 index (33%) suggesting malignant melanoma, the patient exhibited a favorable 5-month outcome. The mitotic activity of the neoplastic cells may not provide a reliable prediction for feline melanocytic tumors.

Mitotic activity: A systematic literature review of the assessment methodology and prognostic value in feline tumors

Increased proliferation is a driver of tumorigenesis, and quantification of mitotic activity is a standard task for prognostication. This systematic review is an analysis of all available references on mitotic activity in feline tumors to provide an overview of the assessment methods and prognostic value. A systematic literature search in PubMed and Scopus and a nonsystematic search in Google Scholar were conducted. All articles on feline tumors that correlated mitotic activity with patient outcome were identified. Data analysis revealed that of the 42 eligible articles, mitotic count (MC, mitotic figures/tumor area) was evaluated in 39 studies, and mitotic index (MI, mitotic figures/tumor cells) in 3 studies. The risk of bias was considered high for most studies (26/42, 62%) based on small study populations, insufficient details of the MC/MI methods, and lack of statistical measures for diagnostic accuracy or effect on outcome. The MC/MI methods varied between studies. A significant association of MC with survival was determined in 20 of 28 (71%) studies (10 studies evaluated other outcome metrics or provided individual patient data), while 1 study found an inverse effect. Three tumor types had at least 4 studies, and a prognostic association with survival was found in 5 of 6 studies on mast cell tumors, 5 of 5 on mammary tumors, and 3 of 4 on soft-tissue sarcomas. MI was shown to correlate with survival for mammary tumors by 2 research groups; however, comparisons to MC were not conducted. Further studies with standardized mitotic activity methods and appropriate statistical analysis for discriminant ability of patient outcome are needed to infer the prognostic value of MC and MI.

First description of oesophageal melanoma in a cat and palliative treatment by endoscopic argon plasma coagulation laser

Case summary

An 11-year-old castrated male domestic shorthair cat presented with chronic regurgitation and weight loss. Despite a 2-month history of weight loss, regurgitation intensified over 4 weeks, occurring with every food intake, even on a semi-liquid diet. Physical examination revealed thinness and dehydration, and a focal oval mass was noted in the middle mediastinum on thoracic radiography. Oesophagoscopy identified a 6 cm neoformation almost completely obstructing the oesophageal lumen. Biopsies were taken and histopathology, positivity to melanoma triple cocktail and PNL-2 by immunohistochemistry led to the diagnosis of melanocytic neoplasm. Palliative debulking with argon plasma coagulation (APC) was performed, significantly improving the cat's quality of life for 2 months. The cat survived for 107 days after diagnosis.

Relevance and novel information

This case report describes the first report of melanocytic neoplasia originating from the oesophageal mucosa in a cat. In cats, melanomas outside the eyes are exceedingly rare and oesophageal neoplasms are exceptionally rare in veterinary medicine, particularly melanomas. The diagnosis relied on positive immunohistochemistry markers aligning with previous research. Treatment with APC emerged as a novel, potentially palliative approach, successfully alleviating regurgitation for 3 months. This underscores APC's potential in feline oesophageal neoplasia palliative care, which deserves further investigation in a broader feline cohort to confirm its efficacy. Overall, this report provides valuable insights into the diagnosis and treatment of oesophageal melanoma in cats.

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.

Feline Oral Melanoma-A Retrospective Study in 20 Cats and Case Report

This retrospective study reported the clinical presentation, histopathologic findings, treatment, results of clinical staging, necropsy findings, and survival times for 20 cats with oral melanoma. The median survival time was 102 days, with a one-year survival rate of 15% (n = 3). Metastatic disease was documented in 5 cases. Cats with metastatic disease, tumors within the oral cavity (in contrast to labial tumors), and those treated only palliatively after diagnosis had shorter survival times. One case was monitored from the time of presentation until euthanasia.

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.

Electrochemotherapy as a treatment option for feline nasal melanoma

Case summary

A 4-year-old domestic shorthair cat presented to North Downs Specialist Referrals for treatment of a 7 mm melanoma of the nasal planum. Two treatments of electrochemotherapy using intravenous bleomycin as a chemotherapeutic agent were administered. The tumour was no longer visible after treatment. At the 292-day follow-up there was no recurrence at the site and the patient was clinically well.

Relevance and novel information

There are few data concerning the outcomes of cats with non-ocular feline melanomas and there are currently minimal descriptions in the literature of electrochemotherapy as a treatment option. The available data suggest that nasal melanoma may have a worse prognosis, and that melanomas are locally invasive and have a high propensity for metastasis. The current most effective means for local control is surgery with wide margins. Given the location in this case, this would have required nasal planectomy, while electrochemotherapy provided an effective and possibly more attractive alternative.

Cutaneous Amelanotic Signet-Ring Melanoma in a Siberian Tiger (Panthera tigris altaica)

A 15-year-old male white Siberian tiger (Panthera tigris altaica) was evaluated for an elevated, ulcerated, cutaneous mass on the right flank. The mass was removed by excisional biopsy and submitted for histopathology. Based on distinct histological features of intracytoplasmic globular material and positive immunohistochemical staining for Melan-A and vimentin, an amelanotic signet-ring melanoma was diagnosed. While in domestic cats this neoplasm is associated with malignancy and a short survival time, the tiger had no local recurrence or related clinical disease approximately 4 years post surgery. Cutaneous melanocytic tumours are rare in big cats, and the findings in this case suggest that amelanotic signet-ring melanoma is not as malignant as its counterpart in domestic cats.

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.

Metastatic Cutaneous Melanoma in a White African Lioness (Panthera leo)

Malignant melanomas tend to be locally destructive, aggressive tumours commonly associated with recurrence and/or metastasis. In this report, a 13-year-old captive white African lioness (Panthera leo), with a recent history of intermittent bouts of lethargy and inappetence, presented with a distended abdomen (due to ascites) and a small, round crusty lesion on the ear. An abdominal ultrasound showed the presence of masses on the liver and an exploratory laparotomy revealed multiple pale lesions on the liver and omentum. Histopathology revealed sheets of pleomorphic neoplastic cells compressing the non-neoplastic liver tissue. Similar neoplastic cells had multifocally expanded and effaced omentum adipose tissue, as well as formed a well-circumscribed mass in the ear sample, extending from close to the epidermis to the lateral and deep margins of the section. All three tissue samples had a high mitotic index (15 per 10 HPF), and critically, in the ear sample, there were rafts of neoplastic cells in the lymphatics, indicating lymphovascular invasion. Immunohistochemistry for the melanoma marker, PNL-2, showed strong positivity in all three tissue samples. Thus, the diagnosis was of malignant melanoma with metastasis to the liver and omentum. This is the first report of metastatic cutaneous melanoma in a lion.

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.

Melanocytic tumours of the nasal planum in cats: 10 cases (2004-2019)

OBJECTIVES

To better characterise signalment, biologic behaviour, and treatment outcome in melanocytic tumours of the nasal planum in cats.

MATERIALS AND METHODS

Retrospective study in cats diagnosed with histopathologically confirmed melanocytic tumours on the nasal planum.

RESULTS

Ten cats were identified with melanocytic tumours of the nasal planum. Pigmentation of the nasal planum seemed to be a predisposing factor. Seven cats were diagnosed histopathologically with a malignant melanoma, three with a benign melanocytoma. One of the cats developed a lymph node metastasis despite diagnosis of a well-differentiated melanocytic neoplasia. In four cases, a pigmented mass, which was initially stable over a long time, showed a sudden rapid progression suggesting malignant transformation. Treatments included hypofractionated radiation therapy (n = 6) and surgical resection (n = 1). In three cats no further treatment was pursued. Complete (n = 3) and partial (n = 3) remissions were observed in cats treated with radiation therapy; however, all experienced tumour progression or recurrence after a short period of time. Most of the cats (n = 7) had to be euthanased due to tumour progression (median survival time: 265 days).

CLINICAL SIGNIFICANCE

The present case series provides insights in clinical presentation and clinical outcomes of cats with melanocytic tumours of the nasal planum.