Comparison of DNA extraction methods for genotyping equine histidine-rich glycoprotein insertion/deletion polymorphisms using oral mucosa swabs and feces

Previously, we demonstrated unique insertion/deletion polymorphisms of equine histidine-rich glycoprotein (eHRG) with five genotypes composed of 45-bp or 90-bp deletions in the histidine-rich region of eHRG in Thoroughbred horses. Although leukocytes are typically used to collect DNA for genotyping, blood sampling from animals is sometimes difficult and invasive. Moreover, the method for extracting DNA from blood leukocytes involves complicated steps and must be performed soon after blood sampling for sensitive gene analysis. In the present study, we performed eHRG genotyping using DNA, isolated from oral mucosa swabs collected by rubbing the mucosa on the underside of the upper lip of horses and 100 mg of freshly excreted feces obtained by scraping their surface. In the present study, we performed eHRG genotyping using DNA isolated from oral mucosa swabs and feces of horses (18 Thoroughbreds, 17 mixed breeds, 2 warm bloods), and compared the accuracy of this method with that of the method using DNA from leukocytes. The DNA derived from oral mucosa swabs was sufficient in quantity and quality for eHRG genotyping. However, DNA derived from fecal samples requires a more sensitive detection system because of contamination with non-horse DNA, and the test quality is low. Collection of oral mucosa swabs is less invasive than blood sampling; further, oral swabs can be stored for a longer period in a specified high-quality solution. Therefore, collecting DNA samples from oral mucosa swabs is recommended for the genetic analysis of not only horses but also other animals that are not accustomed to humans.

Clinical Use of Molecular Biomarkers in Canine and Feline Oncology: Current and Future

Molecular biomarkers are central to personalised medicine for human cancer patients. It is gaining traction as part of standard veterinary clinical practice for dogs and cats with cancer. Molecular biomarkers can be somatic or germline genomic alterations and can be ascertained from tissues or body fluids using various techniques. This review discusses how these genomic alterations can be determined and the findings used in clinical settings as diagnostic, prognostic, predictive, and screening biomarkers. We showcase the somatic and germline genomic alterations currently available to date for testing dogs and cats in a clinical setting, discussing their utility in each biomarker class. We also look at some emerging molecular biomarkers that are promising for clinical use. Finally, we discuss the hurdles that need to be overcome in going 'bench to bedside', i.e., the translation from discovery of genomic alterations to adoption by veterinary clinicians. As we understand more of the genomics underlying canine and feline tumours, molecular biomarkers will undoubtedly become a mainstay in delivering precision veterinary care to dogs and cats with cancer.

Subcutaneous mast cell tumours: A prospective multi-institutional clinicopathological and prognostic study of 43 dogs

BACKGROUND

Canine subcutaneous mast cell tumours (ScMCTs) reportedly have a good prognosis. However, biomarkers that can be used to predict outcome are currently limited.

METHODS

A multicentre prospective study was conducted to identify new prognostic markers. Dogs with a first occurrence of ScMCT were enrolled upon primary tumour removal and regional lymphadenectomy. In the absence of metastasis, dogs were monitored, while dogs with overtly metastatic lymph nodes (histological node 3, HN3) received adjuvant vinblastine.

RESULTS

Forty-three dogs were enrolled: 15 (34.9%) had at least one HN3 lymph node and received vinblastine, and 28 (65.1%) were monitored. Three tumours harboured exon 8 and 9 c-kit mutations. Eight (18.6%) dogs experienced tumour progression, and five (11.6%) died of MCT-related causes. The 1- and 2-year survival rates were 90% and 77%, respectively. Variables significantly associated with an increased risk of progression included high cytograde, a mitotic count (MC) greater than 4/10 high-power fields (hpf) and Ki67-index greater than 23. An MC greater than 4/10 hpf was also associated with an increased risk of tumour-related death.

LIMITATIONS

Regional rather than sentinel lymphadenectomy was performed in these dogs. Dogs were enrolled in oncology referral centres, constituting a different population compared to previous studies.

CONCLUSIONS

ScMCTs have a good prognosis. However, the metastatic rate at admission was higher in this study than previously reported, and a subset of tumours were associated with a fatal outcome despite multimodal treatment. Proliferative activity and cytograding may predict more aggressive behaviour in ScMCTs.

Immunohistochemical and Molecular Genetic Analysis of Canine Digital Mast Cell Tumours

Grading, immunohistochemistry and c-kit mutation status are criteria for assessing the prognosis and therapeutic options of canine cutaneous mast cell tumours (MCTs). As a subset, canine digital MCTs have rarely been explored in this context. Therefore, in this retrospective study, 68 paraffin-embedded canine digital MCTs were analysed, and histological grading was assessed according to Patnaik and Kiupel. The immunohistochemical markers KIT and Ki67 were used, as well as polymerase chain reaction (PCR) for mutational screening in c-kit exons 8, 9, 11 and 14. Patnaik grading resulted in 22.1% grade I, 67.6% grade II and 10.3% grade III tumours. Some 86.8% of the digital MCTs were Kiupel low-grade. Aberrant KIT staining patterns II and III were found in 58.8%, and a count of more than 23 Ki67-positive cells in 52.3% of the cases. Both parameters were significantly associated with an internal tandem duplication (ITD) in c-kit exon 11 (12.7%). French Bulldogs, which tend to form well-differentiated cutaneous MCTs, had a higher proportion of digital high-grade MCTs and ITD in c-kit exon 11 compared with mongrels. Due to its retrospective nature, this study did not allow for an analysis of survival data. Nevertheless, it may contribute to the targeted characterisation of digital MCTs.

Canine mast cell tumours part I: Clinical and survival outcomes

BACKGROUND

Dogs have a species-specific susceptibility for developing mast cell tumours (MCTs). Mutations in the KIT proto-oncogene (KIT) are known to contribute to the neoplastic biology of mast cells. In dogs, the most common KIT mutation is an internal tandem duplication (ITD) in exon 11 which has been considered a useful prognostic supplement to traditional histopathological tumour grading.

OBJECTIVE

The aim of this retrospective study was to explore the importance of KIT exon 11 ITD mutation status and known clinical and pathological indices in predicting prognosis in a cohort of Australian dogs diagnosed with MCT.

METHODS

Clinical parameters, survival data, and KIT mutation status were collected and assessed for 220 dogs with cutaneous or subcutaneous MCT (n = 189 and n = 31, respectively).

RESULTS

In at least one of the multivariable models, tumour grade (cutaneous Kiupel low or high grade) or tumour subcutaneous location, multiple concurrent MCTs, metastasis at the time of surgery, and senior age were statistically significant in predicting the outcome (MCT-related death and/or second MCT diagnosis) at 6- or 12-month post-tumour excision. KIT exon 11 ITD mutation status was not a significant predictor in any of the final multivariable models and was strongly correlated with high histological grade (p < 0.001).

CONCLUSION

In this sample of dogs, tumour histological grading remained the single most powerful prognostic indicator for MCT outcome. However, concurrent evaluation of multiple prognostically significant parameters provides information of potential value to inform therapeutic management for each patient.

Prognostic value of immunohistochemical markers in canine cutaneous mast cell tumours: A systematic review and meta-analysis

Histological grading systems remain cornerstones in the prognosis of canine cutaneous mast cell tumours (MCTs), but the distinct biological behaviour of each tumour often necessitates the use of complementary markers. Although a plethora of immunohistochemical markers have been proposed as prognostic factors, few are presently applied in routine diagnosis. This systematic review and meta-analysis was designed to establish which immunohistochemical markers have verifiable prognostic value for cutaneous MCTs in dogs. A Boolean search of five databases identified 200 articles for screening, of which 73 were selected for full-text assessment and 24 ultimately included in the systematic review. Odds Ratio (OR) was adopted as the summary measure for subsequent meta-analysis but only 15 articles, relating to the immunomarkers Ki-67 (9), KIT (5), and BAX (2), provided either a value for OR or sufficient data to calculate this statistic. Meta-analysis verified that canine cutaneous MCTs with elevated expression of Ki-67 or BAX, as well aberrant immuno-expression of KIT, showed an increased odds of death, with respective OR values of 11.2 (95% CI 6.3-20.0; p < .01), 9.9 (95% CI 1.3-73.6; p = .03), and 4.1 (95% CI 1.1-15.3; p = .03). Despite KIT, Ki67, and BAX arise as suitable prognostic factor for canine MCTs, this study highlighted the lack of important clinical and statistical data in many published articles, rendering it impossible to complete the meta-analysis of several potentially valuable immunohistochemical markers.

RNAScope in situ Hybridization as a Novel Technique for the Assessment of c-KIT mRNA Expression in Canine Mast Cell Tumor

RNA is considered as an indicator of the dynamic genetic expression changes in a cell. RNAScope is a commercially available in situ hybridization assay for the detection of RNA in formalin-fixed paraffin-embedded tissue. In this work, we describe the use of RNAScope as a sensitive and specific method for the evaluation of c-KIT messenger RNA (mRNA) in canine mast cell tumor. We investigated the expression of c-KIT mRNA with RNAscope in 60 canine mast cell tumors (MCTs), comparing it with the histological grade and KIT immunohistochemical expression patterns. Our results showed an overall good expression of c-KIT mRNA in neoplastic cells if compared with control probes. We also observed a statistically significant correlation between histological grade and c-KIT mRNA expression. No correlations were found between KIT protein immunohistochemical distribution pattern and c-KIT mRNA expression or histological grade. Our results provide a reference basis to better understand c-KIT mRNA expression in canine MCTs and strongly encourage further studies that may provide useful information about its potential and significant role as a prognostic and predictive biological marker for canine MCTs clinical outcome.

Internal Tandem Duplication of Exon 8 of c-kit Is Associated With Longer Total Survival in Canine Cutaneous Mast Cell Tumors

Canine cutaneous mast cell tumors (ccMCTs) have a highly variable biological behavior and accurate prognostication is essential for therapeutic intervention. Internal tandem duplications (ITD) of exon 11 are the most commonly detected c-kit mutation in ccMCTs and are associated with poor prognosis and increased cellular proliferation. The prognostic value of detecting mutations in other exons of c-kit has not been systematically examined. In this study, we analyzed the prognostic value of ITD mutations of exon 8 in c-kit of ccMCTs in comparison to ccMCTs with ITD mutations of exon 11 and ccMCTs without mutations of exon 8 or 11. The mutational status, histological grade, KIT expression pattern, Ki67 index, AgNOR (argyrophilic nucleolar organizing region) score, and Ag67 score were determined in 221 ccMCTs, and outcome was available for 101 dogs. ITD mutations of exon 8 were found in 73/221 (33%), of exon 11 in 100/221 (45%), and none of these mutations in 50/221 (22%) of ccMCTs. None of the dogs with mutations of exon 8 died due to suspected ccMCT-related cause, but 23% dogs with ccMCTs with mutations of exon 11 died due to suspected ccMCT-related cause. Prognostic parameters in ccMCTs with exon 11 mutations were commonly associated with a high proliferative activity and poor prognosis, while prognostic markers in ccMCTs with mutations of exon 8 had lower values similar to those observed in ccMCTs without mutations in exons 8 or 11 of c-kit. This study indicates that screening for ITD mutations in exon 8 in ccMCTs may be helpful to identify less aggressive ccMCTs and may be recommended as a supplementary prognostic test.

In situ c-KIT mRNA quantification of canine cutaneous mast cell tumours and its relationship to prognostic factors

Cutaneous mast cell tumours (MCTs) are the most frequent malignant skin tumours in dogs. Mutations in the c-KIT proto-oncogene are correlated with the pathogenesis and aggressiveness of MCTs. To date, studies have focused on c-KIT mutations and KIT protein localization, with a general lack of mRNA-level analyses. In this study, c-KIT mRNA expression was investigated in canine MCTs by RNA in situ hybridization (RNA-ISH). Furthermore, we evaluated associations between c-KIT mRNA expression and the histological grade, KIT immunohistochemical staining pattern and other clinicopathological parameters. c-KIT mRNA expression was observed in all MCT samples, appearing as clusters of dots in the cytoplasm of neoplastic cells. A significant correlation was detected between c-KIT mRNA expression (quantified according to the H-score and the percentage of positive cells) and the histological grade (determined using two-and three-tier grading systems; P < .05). We also found a significant positive correlation (all P < .05) between c-KIT mRNA expression and the proliferation indices (mitotic index, Ki-67, and Ag67). However, no significant associations with c-KIT expression from RNA-ISH were found with respect to different KIT staining patterns. Overall, these results demonstrate that c-KIT mRNA expression might be an additional tool for measuring the c-KIT status in canine cutaneous MCTs and could serve as a potential prognostic factor. Further studies should evaluate the prognostic significance of c-KIT mRNA expression in a large and uniform cohort of canine MCTs.

Evaluation of a modified proportional margin approach for complete surgical excision of canine cutaneous mast cell tumours and its association with clinical outcome

Canine cutaneous mast cell tumours (MCTs) represent a common neoplasm in veterinary practice. Several reported techniques are available to guide surgical excision. Our study examined one hundred cutaneous MCTs that were excised surgically using a modified proportional margin approach. A 2 cm lateral margin upper limit was applied for any tumour diameter that exceeded this size with a deep surgical margin of one fascial plane applied. A retrospective, cross-sectional study with follow-up was used to determine the clinical utility of this excision technique. Associations between explanatory variables of tumour size and grade were compared with outcomes of complete excision and size of histologic tumour-free margins (HTFM) using the appropriate Pearson's χ² and Fisher's exact tests. Follow-up data evaluated tumour recurrence and patient survival. Ninety-five percent of MCTs (95/100) were completely excised. No significant association in the achievement of complete excision between low- and high-grade MCTs (P = .48) was noted. Tumour size was not associated with the rate of complete excision (P = .06). Tumour grade and size did not influence the size of the HTFM (P = .94 and P = .14, respectively). Overall, a recurrence rate of 3% (3/100 tumours) and de novo MCT development rate of 7.7% (5/65 dogs) was noted, with median follow-up period of 593 days (range 180-1460 days). Post-operative metastases were seen in 4.6% of dogs (3/65). Therefore, a modified proportional margin approach with 2 cm lateral margin upper limit is a suitable technique to guide surgical excision of canine cutaneous MCTs.

Recurrent gene mutations detected in canine mast cell tumours by next generation sequencing

Genetic causes of canine mast cell tumours (MCTs), except for mutations in the KIT gene detected in some MCTs, are generally unknown. We used whole exome sequencing to reveal mutation spectra in canine MCTs. We detected somatic mutations in 87 genes including 10 genes recognized as human cancer drivers. Besides KIT, 14 other genes were recurrently mutated. Subsequently, we performed next generation sequencing of a panel of 50 selected genes in additional MCT samples. In this group, the most frequently altered gene was GNB1 showing a recurrent dinucleotide substitution at position of Gly116 in 30% of the MCT samples (n = 6/20) and Ile80 substitution accompanied by a splice region mutation in one case. We extended the study by analysis of the above mentioned GNB1 regions in additional MCT samples by Sanger sequencing, and assessed the overall prevalence of GNB1 mutations to 17.3% (n = 14/81), which is similar to the prevalence of KIT alterations. Our results indicate that GNB1 mutations are probably involved in canine MCT pathogenesis in both cutaneous and subcutaneous MCT cases. As opposed to KIT alterations, the presence of GNB1 mutations did not negatively affect survival times, and our data even showed a trend towards positive prognosis. If our results are confirmed in a larger number of MCTs, an extension of molecular testing of canine MCTs by GNB1 analysis would help to refine the molecular stratification of MCTs, and become useful for targeted treatment strategies.

Mutation and methylation status of KIT and TP53 in canine cutaneous and subcutaneous mast cell tumours

Cutaneous and subcutaneous mast cell tumours (MCTs) are counted among the most frequent cancers in dogs. However, the genetic aetiology of their development is still mostly unknown, with the exception of KIT and tumor protein p53 (TP₅₃ ) mutations reported in less than a half of cutaneous MCTs. In subcutaneous MCTs, no gene alterations were previously detected. We analysed KIT and TP₅₃ mutations in cutaneous and subcutaneous MCTs, and identified methylated CpG sites in KIT and TP₅₃ promoters and adjacent exon 1 regions. The mutation analysis focused on KIT exons 8, 9 and 11, and TP₅₃ exons 5-8, and revealed mutations in 26% and 7% cutaneous MCT cases, respectively. Moreover, we report a first case of KIT mutation ever detected in subcutaneous MCTs. KIT exon 11 mutations and high Kiupel and Patnaik grades were associated with reduced survival in this study. Both KIT and TP₅₃ gene were generally unmethylated in canine cutaneous MCTs. A sporadic methylation of the CpG positions in KIT promoter and adjacent exon 1 was detected in 70.4% of cutaneous and 82% of subcutaneous MCTs. A sporadic methylation of the CpG positions in the TP₅₃ promoter and exon 1 was observed in 36.8% of the analysed cutaneous MCT samples. Only in two subcutaneous MCTs, we observed more than 30% of clones showing KIT methylation at the CpG positions 13 or 14. The CpG position 14 is involved in a predicted binding site for Sp1 transcription factor. However, the significance of KIT promoter methylation at this specific position needs further evaluation.

Comparative aspects of mast cell neoplasia in animals and the role of KIT in prognosis and treatment

Mast cell neoplasia clinical presentation and biological behaviour vary considerably across mammalian species, ranging from a solitary benign mass to an aggressive systemic malignancy. Mutations in the KIT Proto‐Oncogene Receptor Tyrosine Kinase (KIT) gene are common molecular abnormalities involved in mast cell tumorigenesis. KIT mutations often occur in dog, cat and human neoplastic mast cells and result in altered Kit protein structure and function. In dogs, certain KIT mutations are associated with more malignant and lethal disease. In contrast, KIT mutations in feline and human mast cell neoplasms are not correlated with prognosis, but are of value in diagnosis and treatment planning in humans. KIT genetic abnormalities have not been well investigated in other species, although aberrant cytoplasmic Kit protein staining detected in neoplasms of the ferret, horse and cow resembles aberrant Kit staining patterns detected in neoplastic mast cells of dogs, cats and humans. Mutations within KIT are classified as either regulatory‐type or enzymatic pocket‐type mutations according to their location within the KIT Proto‐Oncogene. Mutations within the enzymatic pocket domain confer tumour resistance to tyrosine kinase inhibitors (TKIs). Hence, knowledge of tumour KIT mutation status adds valuable information for optimizing patient treatment strategies. The use of TKIs in combination with conventional chemotherapeutics has opened a new treatment avenue for patients unresponsive to existing drugs. This review highlights the similarities and differences of mast cell neoplasia in mammals with a special focus on the involvement of KIT in the canine and feline forms in comparison to human mast cell neoplasia.

Prognostic and predictive significance of KIT protein expression and c-kit gene mutation in canine cutaneous mast cell tumours: A consensus of the Oncology-Pathology Working Group

One of the primary objectives of the Oncology-Pathology Working Group (OPWG), a joint initiative of the Veterinary Cancer Society and the American College of Veterinary Pathologists, is for oncologists and pathologists to collaboratively generate consensus documents to standardize aspects of and provide guidelines for oncologic pathology. Consensus is established through critical review of peer-reviewed literature relevant to a subgroup's particular focus. Subsequent acceptance and approval of the document by the OPWG membership at large establishes consensus. The intent of this publication is to help educate practitioners and pathologists on the value of diagnostics related to the KIT receptor tyrosine kinase for canine cutaneous mast cell tumours and to provide a guide for the use of these tests in veterinary medicine. This document represents the opinions of the OPWG and the authors and does not constitute a formal endorsement by the American College of Veterinary Pathologists or the Veterinary Cancer Society.

Oncolytic Sendai Virus Therapy of Canine Mast Cell Tumors (A Pilot Study)

Background: Canine mastocytomas (mast cell tumors) represent a common malignancy among many dog breeds. A typical treatment strategy for canine mastocytomas includes surgery, chemo- and radio-therapy, although in many cases the therapy fails and the disease progression resumes. New treatment approaches are needed. Aims: The goal of this pilot study was to examine safety and efficacy of oncolytic Sendai virus therapy administered to canine patients with cutaneous or subcutaneous mastocytomas. Materials and Methods: Six canine patients, with variable grades and stages of the disease, received virus therapy, either as a monotherapy, or in combination with surgery. The therapy included two or more virus applications administered weekly or biweekly. Each application of Sendai virus (107-108.6 EID50) consisted of multiple individual 0.01-0.1 ml injections delivered intratumorally, intradermally around a tumor, and under a tumor bed. Results: The treatment was well tolerated, with minor transitory side effects. Of the six dogs, two did not receive surgery or any other treatment besides the virus injections. The other four animals underwent radical or debulking surgeries, and in three of them the subsequent administration of Sendai virus completely cleared locally recurrent or/and remaining tumor masses. Five dogs demonstrated a complete response to the treatment, the animals remained disease free during the time of observation (2-3 years). One dog responded only partially to the virotherapy; its after-surgical recurrent tumor and some, but not all, metastases were cleared. This dog had the most advanced stage of the disease with multiple enlarged lymph nodes and cutaneous metastases. Conclusion: The results of the pilot study suggest that Sendai virus injections could be safe and efficient for the treatment of dogs affected by mastocytomas.They also suggest the need of further studies for finding optimal schemes and schedules for this kind of therapy.

Assessment of Canine Mast Cell Tumor Mortality Risk Based on Clinical, Histologic, Immunohistochemical, and Molecular Features

Mast cell tumor (MCT) is a frequent cutaneous neoplasm in dogs that is heterogeneous in clinical presentation and biological behavior, with a variable potential for recurrence and metastasis. Accurate prediction of clinical outcomes has been challenging. The study objective was to develop a system for classification of canine MCT according to the mortality risk based on individual assessment of clinical, histologic, immunohistochemical, and molecular features. The study included 149 dogs with a histologic diagnosis of cutaneous or subcutaneous MCT. By univariate analysis, MCT metastasis and related death was significantly associated with clinical stage ( P < .0001, rP = –0.610), history of tumor recurrence ( P < .0001, rP = –0.550), Patnaik ( P < .0001, rP = –0.380) and Kiupel grades ( P < .0001, rP = –0.500), predominant organization of neoplastic cells ( P < .0001, rP = –0.452), mitotic count ( P < .0001, rP = –0.325), Ki-67 labeling index ( P < .0001, rP = –0.414), KITr pattern ( P = .02, rP = 0.207), and c-KIT mutational status ( P < .0001, rP = –0.356). By multivariate analysis with Cox proportional hazard model, only 2 features were independent predictors of overall survival: an amendment of the World Health Organization clinical staging system (hazard ratio [95% CI]: 1.824 [1.210-4.481]; P = .01) and a history of tumor recurrence (hazard ratio [95% CI]: 9.250 [2.158-23.268]; P < .001]. From these results, we propose an amendment of the WHO staging system, a method of risk analysis, and a suggested approach to clinical and laboratory evaluation of dogs with cutaneous MCT.

Cytologic Criteria for Mast Cell Tumor Grading in Dogs With Evaluation of Clinical Outcome

A 2-tiered histologic grading scheme for canine cutaneous mast cell tumors (MCTs) is based on morphologic characteristics of neoplastic cells, including karyomegaly, multinucleation, nuclear pleomorphism, and mitotic figures. Aspirates from MCTs may provide the same information more quickly, inexpensively, and less invasively. This study used these criteria to develop a cytologic grading scheme for canine MCTs to predict outcome. Three anatomic pathologists graded histologic samples from 152 canine MCTs. Three clinical pathologists evaluated aspirates from these masses using similar criteria. A cytologic grading scheme was created based on correlation with histologic grade and evaluated with a kappa statistic. Survival was evaluated with Kaplan-Meier survival curves. Cox proportional hazards regression was used to estimate hazard ratios for tumor grades and individual grading components. Simple logistic regression tested for relationships between risk factors and mortality. The cytologic grading scheme that best correlated with histology (kappa = 0.725 ± 0.085) classified a tumor as high grade if it was poorly granulated or had at least 2 of 4 findings: mitotic figures, binucleated or multinucleated cells, nuclear pleomorphism, or >50% anisokaryosis. The cytologic grading scheme had 88% sensitivity and 94% specificity relative to histologic grading. Dogs with histologic and cytologic high grade MCTs were 39 times and 25 times more likely to die within the 2-year follow-up period, respectively, than dogs with low grade MCTs. High tumor grade was associated with increased probability of additional tumors or tumor regrowth. This study concluded that cytologic grade is a useful predictor for treatment planning and prognostication.

Feline intestinal mast cell tumours: clinicopathological characterisation and KIT mutation analysis

OBJECTIVES

Feline intestinal mast cell tumours (FIMCTs) are rare and reportedly characterised by poor differentiation, aggressive biological behaviour and lack of reliable therapeutic aids. KIT proto-oncogene-activating mutations have never been investigated in these tumours. This study describes the main clinicopathological and microscopic features observed in 17 FIMCTs.

METHODS

Tumour degree of differentiation, proliferative activity, Kit protein expression and KIT mutations were evaluated and correlated with survival to assess their prognostic relevance.

RESULTS

Ten tumours were located in the small intestine, two in the ileocaecocolic junction, and five in the large intestine. Survival times ranged from 3-538 days. Fifteen tumours were evaluated histologically, and there were six well-differentiated, six moderately differentiated and three poorly differentiated FIMCTs. The last showed a medium-to-large deposition of collagen tissue (P <0.001), and significantly higher mitotic and Ki67 indexes compared with more differentiated tumours (P = 0.011). On survival analysis, tumour degree of differentiation (P <0.001) and a mitotic index >2 (P = 0.022) were significantly associated with decreased survival times. Twelve cases showed Kit protein immunoexpression. The Kit pattern was membranous in five cases (33.3%), focal paranuclear in five (33.3%) and diffuse cytoplasmic in two (13.3%). Cytoplasmic Kit patterns were associated with a lesser differentiation (P = 0.015). Mutation analysis was successfully performed on 12 primary tumours and four lymph node metastases; however, no encoding mutation was detected.

CONCLUSIONS AND RELEVANCE

Contrary to reports in the literature, FIMCTs seem to have an extremely variable biological behaviour. We propose a classification based on tumour degree of differentiation and proliferative activity. These findings need to be confirmed in larger series, and exploration of further genomic regions of KIT is warranted to clarify its role in the development and progression of these neoplasms.

Transcriptomic analysis identified up-regulation of a solute carrier transporter and UDP glucuronosyltransferases in dogs with aggressive cutaneous mast cell tumours

Gene expression analyses have been recently used in cancer research to identify genes associated with tumorigenesis and potential prognostic markers or therapeutic targets. In the present study, the transcriptome of dogs that had died because of mast cell tumours (MCTs) was characterised to identify a fingerprint having significant influence on prognosis determination and treatment selection. A dataset (GSE50433) obtained using a commercial canine DNA microarray platform was used. The transcriptome of seven biopsies obtained from dogs with histologically confirmed, surgically removed MCTs, treated with chemotherapy, and dead for MCT-related causes, was compared with the transcriptional portrait of 40 samples obtained from dogs with histologically confirmed, surgically removed MCTs and that were still alive at the end of the follow-up period. Among the differentially expressed genes (DEGs), eight transcripts were validated by quantitative real time PCR and their mRNA levels were measured in a cohort of 22 additional MCTs. Statistical analysis identified 375 DEGs (fold change 2, false discovery rate 5%). The functional annotation analysis indicated that the DEGs were associated with drug metabolism and cell cycle pathways. Particularly, members of solute carrier transporter (SLC) and UDP glucuronosyltransferase (UGT) gene families were identified as dysregulated. Principal component analysis (PCA) of the 22 additional MCTs identified the separate cluster dogs dead for MCT-related causes. SLCs and UGTs have been recently recognised in human cancer as important key factors in tumour progression and chemo-resistance. An in-depth analysis of their roles in aggressive canine MCT is warranted in future studies.

C-kit as a prognostic and therapeutic marker in canine cutaneous mast cell tumours: From laboratory to clinic

Cutaneous mast cell tumours (MCTs) are some of the most common canine neoplasms and their variable and often aggressive biological behaviour makes them particularly challenging for the veterinary practitioner. Over the years, scientists have accumulated a wealth of knowledge on these tumours and developed better prognostic markers and targeted therapies, mostly focused on inhibiting c-kit, a protein that plays a major role in the biopathology of MCTs. Masitinib and toceranib, targeted inhibitors of c-kit and other receptor tyrosine-kinases (RTKs), offer the promise of improving the outcome of patients with aggressive MCTs. Much of the available knowledge on MCTs is dispersed, making it difficult for practitioners to benefit when consulting a pathologist or making therapeutic decisions. This article seeks to bring together current knowledge on the biopathology of MCTs, reviewing prognostic markers and their applications, and the development of c-kit inhibitors in the context of the basic cellular, molecular and pathological features of MCTs. Future perspectives following recent biopathological data and experimental therapeutic approaches are also addressed.

Sequencing and G-quadruplex folding of the canine proto-oncogene KIT promoter region: might dog be used as a model for human disease?

Downregulation of gene expression by induction of non-canonical DNA structures at promotorial level is a novel attractive anticancer strategy. In human, two guanine-rich sequences (h_kit1 and h_kit2) were identified in the promotorial region of oncogene KIT. Their stabilization into G-quadruplex structures can find applications in the treatment of leukemias, mastocytosis, gastrointestinal stromal tumor, and lung carcinomas which are often associated to c-kit mis-regulation. Also the most common skin cancer in domestic dog, mast cell tumor, is linked to a mutation and/or to an over-expression of c-kit, thus supporting dog as an excellent animal model. In order to assess if the G-quadruplex mediated mechanism of regulation of c-kit expression is conserved among the two species, herein we cloned and sequenced the canine KIT promoter region and we compared it with the human one in terms of sequence and conformational equilibria in physiologically relevant conditions. Our results evidenced a general conserved promotorial sequence between the two species. As experimentally confirmed, this grants that the conformational features of the canine kit1 sequence are substantially shared with the human one. Conversely, two isoforms of the kit2 sequences were identified in the analyzed dog population. In comparison with the human counterpart, both of them showed an altered distribution among several folded conformations.

Evaluation of a modified proportional margins approach for surgical resection of mast cell tumors in dogs: 40 cases (2008-2012)

OBJECTIVE

To evaluate a modified proportional margins approach to resection of mast cell tumors (MCTs) in dogs.

DESIGN

Retrospective case series.

ANIMALS

40 dogs with subcutaneous and cutaneous MCTs undergoing curative intent surgery.

PROCEDURES

Medical records were searched to identify dogs with a cytologically or histologically confirmed diagnosis of MCT that had not previously been treated surgically and that had undergone full oncological staging. In those dogs, tumors were resected with lateral margins equivalent to the widest measured diameter of the tumor and a minimum depth of 1 well-defined fascial plane deep to the tumor. Surgical margins were evaluated histologically. Cutaneous tumors were graded by use of the Patnaik system and the 2-tier system described by Kiupel et al. The prognosis for subcutaneous tumors was assessed in accordance with published recommendations. Follow-up information on dog health status was obtained through clinical examination, the dog owners, and the referring veterinarians.

RESULTS

The 40 dogs had 47 tumors. Forty-one (87%) tumors were cutaneous, and 6 (13%) were subcutaneous. On the basis of the Patnaik system, 21 (51%) cutaneous tumors were considered grade I, 18 (44%) were considered grade II, and 2 (5%) were considered grade III. On the basis of the Kiupel system, 37 (90%) cutaneous tumors were considered low grade, and 4 (10%) were considered high grade. The prognosis for the 6 subcutaneous tumors was classified as likely resulting in a shorter (2) or longer (4) survival time. Forty tumors were deemed to have been excised with clear margins and 7 with incomplete margins. Local recurrence was not recorded for any dog but was suspected for 1 (2%) tumor, although not confirmed. Interval from tumor excision to follow-up ranged from 30 to 1,140 days (median, 420 days).

CONCLUSIONS AND CLINICAL RELEVANCE

The modified proportional margins system resulted in satisfactory local disease control in dogs with MCTs.

Global gene expression analysis of canine cutaneous mast cell tumor: could molecular profiling be useful for subtype classification and prognostication?

Prognosis and therapeutic management of dogs with cutaneous mast cell tumors (MCTs) depend on clinical stage and histological grade. However, the prognostic value of this latter is still questionable. In the present study, MCT transcriptome was analyzed to identify a set of candidate genes potentially useful for predicting the biological behavior of MCTs. Fifty-one canine MCT biopsies were analyzed. Isolated and purified total RNAs were individually hybridized to the Agilent Canine V2 4x44k DNA microarray. The comparison of reference differentiated and undifferentiated MCT transcriptome revealed a total of 597 differentially expressed genes (147 down-regulated and 450 up-regulated). The functional analysis of this set of genes provided evidence that they were mainly involved in cell cycle, DNA replication, p53 signaling pathway, nucleotide excision repair and pyrimidine metabolism. Class prediction analysis identified 13 transcripts providing the greatest accuracy of class prediction and divided samples into two categories (differentiated and undifferentiated), harboring a different prognosis. The Principal Component Analysis of all samples, made by using the selected 13 markers, confirmed MCT classification. The first three components accounted for 99.924% of the total variance. This molecular classification significantly correlated with survival time (p = 0.0026). Furthermore, among all marker genes, a significant association was found between mRNA expression and MCT-related mortality for FOXM1, GSN, FEN1 and KPNA2 (p<0.05). Finally, marker genes mRNA expression was evaluated in a cohort of 22 independent samples. Data obtained enabled to identify MCT cases with different prognosis. Overall, the molecular characterization of canine MCT transcriptome allowed the identification of a set of 13 transcripts that clearly separated differentiated from undifferentiated MCTs, thus predicting outcome regardless of the histological grade. These results may have clinical relevance and warrant future validation in a prospective study.

Histologic grading of canine mast cell tumor: is 2 better than 3?

Mast cell tumor (MCT) is a common canine cutaneous neoplasm with variable biological behavior. A 2-tier histologic grading system was recently proposed by Kiupel et al to reduce interobserver variation and eliminate prognostic uncertainty of the Patnaik system. This study compared the ability of these 2 grading systems to predict survival in a cohort of dogs with MCTs. However, surgical margins were unknown, and the risk of developing new/metastatic MCTs was not studied. Histologic grade was assessed according to both systems for 137 surgically resected cutaneous MCTs. The relationship between grade and survival was evaluated. According to the Patnaik system, 18 MCTs (13.1%) were classified as grade I, 83 (60.6%) as grade II, and 36 (26.3%) as grade III. Grade III was associated with a poorer prognosis (P < .001), but no significant difference between grades I and II was detected. Grading according to the Patnaik system was based on consensus grading among 3 pathologists, and interobserver variability was not considered. All grade I MCTs were low grade in the Kiupel system, and all grade III were high grade. Among grade II, 71 (85.6%) were low grade, and 12 (14.4%) were high grade, with a 1-year survival probability of 94% and 46%, respectively (P < .001). The 2-tier system had a high prognostic value and was able to correctly predict the negative outcomes of some grade II MCTs. Data also confirm that histologic grading cannot predict biological behavior of each MCT and should be supplemented with molecular methods for more accurate prognostication.

DNA and RNA isolation from canine oncologic formalin-fixed, paraffin-embedded tissues for downstream "-omic" analyses: possible or not?

Formalin-fixed, paraffin-embedded (FFPE) tissues represent a unique source of archived biological material, but obtaining suitable DNA and RNA for retrospective "-omic" investigations is still challenging. In the current study, canine tumor FFPE blocks were used to 1) compare common commercial DNA and RNA extraction kits; 2) compare target gene expression measured in FFPE blocks and biopsies stored in a commercial storage reagent; 3) assess the impact of fixation time; and 4) perform biomolecular investigations on archival samples chosen according to formalin fixation times. Nucleic acids yield and quality were determined by spectrophotometer and capillary electrophoresis, respectively. Quantitative real-time polymerase chain reaction assays for the following genes: BCL-2-associated X protein, B-cell lymphoma extra large, antigen identified by monoclonal antibody Ki-67, proto-oncogene c-KIT (c-kit). Two internal control genes (Golgin A1 and canine transmembrane BAX inhibitor motif containing 4), together with direct sequencing of c-kit exons 8, 9, 11, and 17, were used as end points. Differences in DNA/RNA yield and purity were noticed among the commercial kits. Nucleic acids (particularly RNA) extracted from paraffin blocks were degraded, even at lower fixation times. Compared to samples held in the commercial storage reagent, archived tissues showed a poorer amplification. Therefore, a gold standard protocol for DNA/RNA isolation from canine tumor FFPE blocks for molecular investigations is still troublesome. More standardized storage conditions, including time between sample acquisition and fixation, fixation time, and sample thickness, are needed to guarantee the preservation of nucleic acids and, then, their possible use in retrospective transcriptomic analysis.

Modulation of c-kit expression in pancreatic adenocarcinoma: a novel stem cell marker responsible for the progression of the disease

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers because of late symptoms and resistance to chemotherapy and radiation therapy. We have investigated the appearance of c-kit, a stem cell marker, in both normal adult pancreatic tissue and in cancerous tissue. Apart from some very pale staining of islets of Langerhans, normal pancreas was devoid of staining with antibodies to c-kit. In contrast, in cancerous tissue that still preserves the overall integrity of the pancreatic tissue, there was a clear labeling in islets of Langerhans, which seemed to be co-localized with insulin containing β cells. In other cases, where the pancreatic tissue was completely deteriorated, intensive labeling was clearly evident in remnants of both the exocrine and the endocrine tissues. The duct cells of the adenocarcinoma were moderately but clearly labeled with antibodies to c-kit. In contrast, in metastasis of PDAC, very intensive labeling of c-kit was evident. The location of KRAS, which is strongly associated with PDAC, was also analyzed at the initial stages of the disease, when islets of Langerhans still preserve their integrity to a large extent. KRAS was found exclusively in islets of Langerhans and overlapped in its location with insulin and c-kit expressing cells. It is suggested that the modulation of the expression of c-kit, visualized by antibodies to the oncogene molecule, may play an important role in the formation and progression of PDAC. The absence of c-kit in normal pancreas and its appearance in PDAC is probably due to a mutational event, which probably allows conversion of the β cells into cancer stem cells (CSC). Co-expression of both c-kit and KRAS, typical markers for CSC with overlapping with insulin in islets of Langerhans, strongly support the notion that β-cells play a central role in the development of PDAC. The use of specific drugs that can attenuate the kinase activity of c-kit or target KRAS expressing cancer cells should be tested in order to attenuate the progression of this lethal disease.

Concordance of c-kit mutational status in matched primary and metastatic cutaneous canine mast cell tumors at baseline

Background

Mutation analysis of proto‐oncogene c‐kit (c‐kit) is advisable before starting treatment with tyrosine kinase inhibitors in dogs with mast cell tumor (MCT), including those with metastatic disease. Testing is usually performed on primary tumors, assuming that c‐kit mutation status does not change in metastasis.

Hypothesis/Objectives

To give an insight into the mutational processes and to make a recommendation on the use of c‐kit mutational analysis in the clinical setting.

Animals

Twenty‐one client‐owned dogs with metastatic MCT.

Methods

Dogs undergoing resection or biopsy for both primary and matched metastatic MCT were prospectively enrolled. Total RNA or DNA was extracted from primary MCT and corresponding metastases. Exons 8, 9, and 11 were amplified by PCR and sequenced. Genetic features between primary MCT and metastases were compared. Their correlation with clinicopathologic features was investigated.

Results

Concordance (mutated or wild‐type) of mutational status, evaluable in 21 primary and matched metastatic (20 nodal and 1 splenic) MCTs, was 100%. Three new c‐kit mutations were identified. No significant correlation was detected between c‐kit mutation and clinicopathologic features.

Conclusions and Clinical Importance

Proto‐oncogene c‐kit mutational status is conserved between any primary and its matched secondary tumor, suggesting that both can be used for c‐kit mutational testing. Targeted therapies might be also used to treat metastatic disease.

Analysis of activated platelet-derived growth factor β receptor and Ras-MAP kinase pathway in equine sarcoid fibroblasts

Equine sarcoids are skin tumours of fibroblastic origin affecting equids worldwide. Bovine papillomavirus type-1 (BPV-1) and, less commonly, type-2 are recognized as etiological factors of sarcoids. The transforming activity of BPV is related to the functions of its major oncoprotein E5 which binds to the platelet-derived growth factor β receptor (PDGFβR) causing its phosphorylation and activation. In this study, we demonstrate, by coimmunoprecipitation and immunoblotting, that in equine sarcoid derived cell lines PDGFβR is phosphorylated and binds downstream molecules related to Ras-mitogen-activated protein kinase-ERK pathway thus resulting in Ras activation. Imatinib mesylate is a tyrosine kinase receptors inhibitor which selectively inhibits the activation of PDGFβR in the treatment of several human and animal cancers. Here we show that imatinib inhibits receptor phosphorylation, and cell viability assays demonstrate that this drug decreases sarcoid fibroblasts viability in a dose-dependent manner. This study contributes to a better understanding of the molecular mechanisms involved in the pathology of sarcoids and paves the way to a new therapeutic approach for the treatment of this common equine skin neoplasm.

Evaluation of tyrosine-kinase receptor c-kit mutations, mRNA and protein expression in canine lymphoma: might c-kit represent a therapeutic target?

c-kit plays an important role in proliferation, survival and differentiation of hematopoietic progenitor cells. In human hematopoietic malignancies, c-kit is mostly expressed by progenitor cell neoplasms and seldom by mature cell neoplasms. Aim of this study was to evaluate c-kit expression in canine lymphoma. Twenty-five B-cell lymphomas and 21 T-cell lymphomas were enrolled in the study. c-kit mRNA and protein expression was measured in lymph node fine needle aspirates by quantitative real-time RT-PCR, flow cytometry and immunocytochemistry, while the occurrence of KIT mutations on exons 8-11 and 17 was investigated by direct cDNA sequencing. KIT mRNA was amplifiable but below the limit of quantification in 76% of B-cell lymphomas and 33% of T-cell lymphomas. Remaining samples showed a very low expression of KIT, except for some high grade (HG) T-cell lymphomas where a comparatively higher mRNA amount was observed. Transcriptional data were confirmed at the protein level. No gain-of-function mutations were observed. Among canine lymphomas, T-cell lymphoma typically shows an aggressive biological behavior, partly being attributable to the lack of efficacious treatment options, and the evidence of c-kit expression in HG T-cell lymphomas might represent the rationale for its routinely diagnostic evaluation and the use of tyrosine kinase inhibitors in future clinical trials.

Evaluation of tyrosine-kinase receptor c-KIT (c-KIT) mutations, mRNA and protein expression in canine leukemia: might c-KIT represent a therapeutic target?

The tyrosine-kinase receptor c-KIT (c-KIT) plays an important role in proliferation, survival and differentiation of progenitor cells in normal hematopoietic cells. In human hematological malignancies, c-KIT is mostly expressed by progenitor cell neoplasia and seldom by those involving mature cells. Tyrosine kinase inhibitors (TKIs) are actually licensed for the first- and second-line treatment of human hematologic disorders. Aim of the present study was to evaluate c-KIT mRNA and protein expression and complementary DNA (cDNA) mutations in canine leukemia. Eleven acute lymphoblastic leukemia (ALL) and acute undifferentiated leukemia (AUL) and 12 chronic lymphocytic leukemia (CLL) were enrolled in this study. The amounts of c-KIT mRNA and protein were determined, in peripheral blood samples, by using quantitative real time RT-PCR, flow cytometry and immunocytochemistry, respectively. The presence of mutations on c-KIT exons 8-11 and 17 were investigated by cDNA sequencing. Higher amounts of c-KIT mRNA were found in ALL/AUL compared to CLL, and this latter showed a lower pattern of gene expression. Transcriptional data were confirmed at the protein level. No significant gain-of-function mutations were ever observed in both ALL/AUL and CLL. Among canine hematological malignancies, ALL/AUL typically show a very aggressive biological behavior, partly being attributable to the lack of efficacious therapeutic options. The high level of c-KIT expression found in canine ALL/AUL might represent the rationale for using TKIs in future clinical trials.