Clustering of activating mutations in c-KIT's juxtamembrane coding region in canine mast cell neoplasms

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.

Clinical, pathologic, and molecular characterization of a non-metastatic multicentric cutaneous mast cell tumor in a cow

Cutaneous mast cell tumors are rarely reported in cattle. Although mutations in the c-KIT gene have been shown to play a central role in the oncogenesis of canine mast cell tumors, few data are available in cattle. This report describes the clinical, histologic, immunohistochemical, and genetic features of a multicentric cutaneous mast cell tumor in an adult cow. An 11-year-old Prim'Holstein cow was presented for a 5-month history of multiple skin nodules. Cytologic and histologic analyses of the nodules led to a diagnosis of mast cell tumors. Immunohistochemical analysis for KIT expression showed a moderate to strong signal in neoplastic mast cells with a cytoplasmic and membranous pattern. Sequencing of the c-KIT gene coding sequence revealed no mutation. Despite partial response after corticosteroid treatment, euthanasia was elected. No metastases to the lymph nodes, spleen, and liver were identified at post-mortem and histologic examinations.

Luteinizing Hormone Receptor Expression in Neoplastic Mast Cells Is Increased in Spayed and Neutered Dogs

Luteinizing hormone receptors (LHRs) are expressed in canine lymphoma and hemangiosarcoma. We hypothesized that LHR would be expressed in canine mast cell tumors (MCTs) and that more neoplastic mast cells would express LHR in gonadectomized dogs compared with intact dogs. Eleven archived formalin-fixed paraffin-embedded cutaneous MCT tissue sections were processed using routine immunohistochemistry. For both the KIT protein and LHR, the percentage of positive cells for each staining pattern (I-III) was calculated. A Student's t test was used to compare the total percentage of positive cells expressing LHR and KIT in intact and gonadectomized dogs. A one-way analysis of variance was used to compare the percentage of cells within each staining pattern for LHR and KIT in intact and gonadectomized dogs. All MCT expressed LHR. MCT from gonadectomized dogs had a significantly higher percentage of LHR-positive mast cells (84.2 ± 8.7%) compared with MCTs from intact dogs (64.3 ± 4.2%). This is the first study to demonstrate the expression of LHR in canine MCTs and to report that LHR expression is increased in neoplastic mast cells from gonadectomized dogs compared with intact dogs. Future studies are planned to evaluate the functionality of the LHR in canine neoplastic mast cells.

Intranasal mast cell tumors: Clinical, immunohistochemical, and molecular features in 20 dogs

Mast cell tumors (MCTs) are an uncommon primary neoplasm of the nasal cavity in dogs for which there is a paucity of existing literature regarding their clinical behavior and molecular features. The objectives of this retrospective study were to examine the clinical findings, histopathologic and immunohistochemical features, and c-KIT mutation status of primary intranasal MCTs in dogs and identify potential prognostic factors. Canine biopsies submitted to a diagnostic laboratory in Colorado between 2010 and 2019 with intranasal neoplasms diagnosed as MCTs and no history of cutaneous or oral MCT were considered. Immunohistochemistry for CD117 and Ki67 and polymerase chain reaction (PCR) for internal tandem duplications at exons 8 and 11 of the c-KIT gene were performed. Twenty out of 1849 (1%) primary intranasal neoplasms were MCTs. Metastases were reported in 11/20 cases (55%), with the mandibular lymph node representing the most common site. One case had distant metastases to abdominal viscera. Of the cases with available outcome data, 6/14 (43%) died or were euthanized from MCT-related disease within 1 year of the onset of clinical signs. Only one case had a c-KIT mutation at exon 11. In our study, intranasal MCTs were prone to metastasize and had a generally poor prognosis, resembling the behavior of MCTs arising in other mucosal locations. While dogs with metastatic disease and survival times of <1 year tended to have atypical KIT localization, moderate to high Ki67 indices, and mitotic counts ≥8, definitive prognosticators could not be identified due to the limited number of cases with favorable clinical outcomes.

Systematic review and meta-analysis of genomic alterations in acral melanoma

Acral melanoma (AM) tumors arise on the palms, soles, fingers, toes, and nailbeds. A comprehensive systematic meta-analysis of AM genomic aberrations has not been conducted to date. A literature review was carried out to identify studies sequencing AM. Whole-genome/exome data from 181 samples were identified. Targeted panel sequencing data from MSK-IMPACT were included as a validation cohort (n = 92), and studies using targeted hot spot sequencing were also collated for BRAF (n = 26 studies), NRAS (n = 21), and KIT (n = 32). Statistical analysis indicated BRAF, NRAS, PTEN, TYRP1, and KIT as significantly mutated genes. Frequent copy-number aberrations were also found for important cancer genes, such as CDKN2A, KIT, MDM2, CCND1, CDK4, and PAK1, among others. Mapping genomic alterations within the context of the hallmarks of cancer identified four components frequently altered, including (i) sustained proliferative signaling and (ii) evading growth suppression, (iii) genome instability and mutation, and (iv) enabling replicative immortality. This analysis provides the largest analysis of genomic aberrations in AM in the literature to date and highlights pathways that may be therapeutically targetable.

Diagnosis, Prognosis and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors

Mast cell tumors (MCTs) are hematopoietic neoplasms composed of mast cells. It is highly common in dogs and is extremely important in the veterinary oncology field. It represents the third most common tumor subtype, and is the most common malignant skin tumor in dogs, corresponding to 11% of skin cancer cases. The objective of this critical review was to present the report of the 2nd Consensus meeting on the Diagnosis, Prognosis, and Treatment of Canine Cutaneous and Subcutaneous Mast Cell Tumors, which was organized by the Brazilian Association of Veterinary Oncology (ABROVET) in August 2021. The most recent information on cutaneous and subcutaneous mast cell tumors in dogs is presented and discussed.

Exon-1 skipping and intron-1 retaining by alternative splicing of the c-KIT gene encodes a novel splice variant in the skin of Merino sheep (Ovis aries)

c-KIT, a type III receptor protein tyrosine kinase, plays an essential role in melanocyte development, migration, and survival. Mutations within the c-KIT gene are previously shown to cause the white coat color phenotypes in pigs, mice, goats, and humans. However, up so far, the splicing isoform(s), genomic architecture of c-KIT have not been characterized well in merino sheep. Reverse transcriptase (RT)-PCR analysis with molecular prediction identified two basic splice variants: Transcript Variant-1, 2 for 12 bp insertion coding sequences (CDS) corresponding to the four amino acids 'GNSK', respectively. Using 5' RACE, here we report for the first time a novel c-KIT 'Transcript Variant-3' from the skin of merino sheep by comparative genome analyses at exon(1)-intron(1)-exon(2) boundaries. In contrast, a single product of 795 bp was characterized by 3' RACE. We also demonstrated that the c-KIT gene expression at the transcript level is not mediated via an intron-9 splicing event. Overall, beyond what was observed in other mammals, our data provide novel insights into the molecular structure of the c-KIT gene in sheep.

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.

KIT mutations in mast cell tumours from cheetahs (Acinonyx jubatus) and domestic cats (Felis catus)

Mast cell tumours (MCT) have been documented in numerous species and mutations within the KIT proto-oncogene are implicated in the neoplastic biology of mast cells in humans, dogs and cats. This study determined high KIT gene nucleotide and Kit amino acid sequence homology between several species known to suffer mast cell neoplasia and especially high sequence conservation between the cheetah (Acinonyx jubatus) and domestic cat (Felis catus) KIT sequences. As a result, we hypothesised that KIT mutations would exist in the neoplastic DNA of four cheetahs diagnosed with MCT from a recent case series. PCR and Sanger sequencing identified conservative exon 6 KIT mutations in two of the four cheetahs. The mutations were different between the two cheetahs. Only wild-type DNA in exons 6, 8, 9 and 11 of KIT was observed in the MCTs of the remaining two cheetahs. Twenty cutaneous MCTs from domestic cats were collected for KIT mutation comparison. Twelve tumours possessed a mutation within KIT exons 6, 8 or 9 (60%, 95% CI 38.5%-81.5%). No mutations were detected in exon 11. There was no significant association between domestic feline MCT KIT mutation status and tumour histological grade (traditional schematic, P = .934; Sabattini 2-tier schematic, P = .762) or mitotic index (P = .750). KIT mRNA and Kit protein sequences are conserved across species but the role of KIT in feline MCT pathogenesis is not completely understood.

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.

High-Grade Cutaneous Mast Cell Tumour with Widespread Intrathoracic Metastasis and Neoplastic Pericardial Effusion in a Dog

An 8-year-old neutered male French Bulldog was presented with a 2-day history of intermittent vomiting, reduced appetite and recent rapid development of multiple cutaneous masses over the head and neck regions. On presentation, the patient had a moderate volume of pericardial and bilateral pleural effusion. Echocardiography demonstrated irregular, heterogeneous thickening of the walls of the right ventricle and right atrium, consistent with infiltrative intramyocardial disease. Cytological examination of fine needle aspirates from one of the cutaneous masses confirmed a mast cell tumour. Pericardial fluid analysis revealed a haemorrhagic neoplastic effusion due to mast cell neoplasia. Histopathological and immunohistochemical examination of tissues obtained post mortem confirmed a high-grade cutaneous mast cell tumour with metastasis to the heart, pericardium, mediastinum and spleen. No metastatic disease was present in the submandibular lymph nodes or liver. Immunohistochemistry demonstrated KIT staining pattern 2. There was strong nuclear Ki67 labelling in an average of 65.0 cells per grid and an average of three positive AgNORs per nucleus in neoplastic cells. Polymerase chain reaction for the activating duplication mutation in exons 8 and 11 of c-Kit were negative. To the authors' knowledge, this is the first report of a canine cutaneous mast cell tumour associated with neoplastic pericardial effusion and widespread intrathoracic metastasis.

Recent Advances in the Molecular Biology of Systemic Mastocytosis: Implications for Diagnosis, Prognosis, and Therapy

In recent years, molecular characterization and management of patients with systemic mastocytosis (SM) have greatly benefited from the application of advanced technologies. Highly sensitive and accurate assays for KIT D816V mutation detection and quantification have allowed the switch to non-invasive peripheral blood testing for patient screening; allele burden has prognostic implications and may be used to monitor therapeutic efficacy. Progress in genetic profiling of KIT, together with the use of next-generation sequencing panels for the characterization of associated gene mutations, have allowed the stratification of patients into three subgroups differing in terms of pathogenesis and prognosis: i) patients with mast cell-restricted KIT D816V; ii) patients with multilineage KIT D816V-involvement; iii) patients with "multi-mutated disease". Thanks to these findings, new prognostic scoring systems combining clinical and molecular data have been developed. Finally, non-genetic SETD2 histone methyltransferase loss of function has recently been identified in advanced SM. Assessment of SETD2 protein levels and activity might provide prognostic information and has opened new research avenues exploring alternative targeted therapeutic strategies. This review discusses how progress in recent years has rapidly complemented previous knowledge improving the molecular characterization of SM, and how this has the potential to impact on patient diagnosis and management.

The secondary KIT mutation p.Ala510Val in a cutaneous mast cell tumour carrying the activating mutation p.Asn508Ile confers resistance to masitinib in dogs

Background

Gain-of-function mutations in KIT are driver events of oncogenesis in mast cell tumours (MCTs) affecting companion animals. Somatic mutations of KIT determine the constitutive activation of the tyrosine kinase receptor leading to a worse prognosis and a shorter survival time than MCTs harbouring wild-type KIT. However, canine MCTs carrying KIT somatic mutations generally respond well to tyrosine kinase inhibitors; hence their presence represents a predictor of treatment effectiveness, and its detection allows implementing a stratified medical approach. Despite this, veterinary oncologists experience treatment failures, even with targeted therapies whose cause cannot be elucidated. The first case of an MCT-affected dog caused by a secondary mutation in the tyrosine kinase domain responsible for resistance has recently been reported. The knowledge of this and all the other mutations responsible for resistance would allow the effective bedside implementation of a deeply stratified and more effective medical approach.

Case presentation

The second case of a canine MCT carrying a different resistance mutation is herein described. The case was characterised by aggressive behaviour and early metastasis unresponsive to both vinblastine- and masitinib-based treatments. Molecular profiling of the tumoural masses revealed two different mutations; other than the already known activating mutation p.Asn508Ile in KIT exon 9, which is tyrosine kinase inhibitor-sensitive, a nearly adjacent secondary missense mutation, p.Ala510Val, which had never before been described, was detected. In vitro transfection experiments showed that the secondary mutation did not cause the constitutive activation by itself but played a role in conferring resistance to masitinib.

Conclusions

This study highlighted the importance of the accurate molecular profiling of an MCT in order to improve understanding of the molecular mechanism underlying tumourigenesis and reveal chemoresistance in MCTs for more effective therapies. The detection of the somatic mutations responsible for resistance should be included in the molecular screening of MCTs, and a systematic analysis of all the cases characterised by unexpected refractoriness to therapies should be investigated in depth at both the genetic and the phenotypic level.

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.

Identifying Candidate Druggable Targets in Canine Cancer Cell Lines Using Whole-Exome Sequencing

Cancer cell culture has been a backbone in cancer research, in which analysis of human cell line mutational profiles often correlates with oncogene addiction and drug sensitivity. We have conducted whole-exome sequence analyses on 33 canine cancer cell lines from 10 cancer types to identify somatic variants that contribute to pathogenesis and therapeutic sensitivity. A total of 66,344 somatic variants were identified. Mutational load ranged from 15.79 to 129.37 per Mb, and 13.2% of variants were located in protein-coding regions (PCR) of 5,085 genes. PCR somatic variants were identified in 232 genes listed in the Cancer Gene Census (COSMIC). Cross-referencing variants with human driving mutations on cBioPortal identified 61 variants as candidate cancer drivers in 30 cell lines. The most frequently mutated cancer driver was TP53 (15 mutations in 12 cell lines). No drivers were identified in three cell lines. We identified 501 non-COSMIC genes with PCR variants that functionally annotate with COSMIC genes. These genes frequently mapped to the KEGG MAPK and PI3K-AKT pathways. We evaluated the cell lines for ERK1/2 and AKT(S473) phosphorylation and sensitivity to the MEK1/2 inhibitor, trametinib. Twelve of the 33 cell lines were trametinib-sensitive (IC₅₀ < 32 nmol/L), all 12 exhibited constitutive or serum-activated ERK1/2 phosphorylation, and 8 carried MAPK pathway cancer driver variants: NF1(2), BRAF(3), N/KRAS(3). This functionally annotated database of canine cell line variants will inform hypothesis-driven preclinical research to support the use of companion animals in clinical trials to test novel combination therapies.

Identification of the two KIT isoforms and their expression status in canine hemangiosarcomas

BACKGROUND

KIT is a tyrosine kinase growth factor receptor. High expression of KIT has been found in several tumors including canine hemangiosarcoma (HSA). This study investigated the correlation of KIT expression and c-kit sequence mutations in canine HSAs and benign hemangiomas (HAs).

RESULTS

Immunohistochemistry (IHC) staining confirmed KIT expression in 94.4 % (34/36) of HSAs that was significantly higher than 0 % in HAs (0/16). Sequencing the entire c-kit coding region of HSAs and normal canine cerebellums (NCCs) revealed GNSK-deletion in exon 9. As for exon 9 genotyping by TA-cloning strategy, GNSK-deletion c-kit accounted for 48.6 % (68/140) colonies amplified from12 KIT-positive HSAs, a significantly higher frequency than 14.1 % (9/64) of colonies amplified from six NCCs.

CONCLUSIONS

Due to the distinct expression pattern revealed by IHC, KIT might be used to distinguish benign or malignant vascular endothelial tumors. Moreover, the high incidence of GNSK-deletion c-kit in canine HSAs implicates KIT isoforms as possibly participating in the tumorigenesis of canine HSAs.

KIT-positive Gastrointestinal Stromal Tumor in a 22-year-old Male Chimpanzee (Pan troglodites)

Gastrointestinal stromal tumors (GIST), KIT-positive and KIT signaling driven or platelet-derived growth factor receptor α (PDGFRA) signaling driven mesenchymal tumors, are poorly known in nonhuman primates. Availability of KIT- and PDGFRA-inhibitor drug imatinib mesylate has greatly raised the interest for these tumors. At necropsy of a 22-year-old male chimpanzee, a round, firm 2-cm intramural tumor was incidentally found in the midbody of the stomach and diagnosed as a GIST. Histologically, the mass was composed of spindle to polygonal epithelioid cells arranged in short to intermediate-length, interlacing streams, bundles, and nodular whorls often separated by hyalinized eosinophilic matrix. The mitotic rate was a maximum 1/50 high-power field. Immunohistochemically, the tumor cells were diffusely positive for KIT and CD34, focally positive for α-smooth muscle actin, and negative for muscle specific actin, desmin, S-100 protein, synaptophy-sin, and glial fibrillary acidic protein. Because the majority of human GISTs have gain-of-function KIT or PDGFRA mutations, genomic sequences of KIT exons 9, 11, 13, and 17 and PDGFRA exons 12 and 18 from this chimpanzee GIST were polymerase chain reaction amplified and sequenced. However, no mutation was identified in the analyzed “mutational hot spots.” This study is the first extensive histomorphologic, immunohistochemical, and molecular genetic analysis of a chimpanzee GIST. More cases of nonhuman primate GISTs should be analyzed to discover the clinicopathologic spectrum of GISTs in these species.

The Use of KIT and Tryptase Expression Patterns as Prognostic Tools for Canine Cutaneous Mast Cell Tumors

Cutaneous mast cell tumors (MCTs) are one of the most common tumors in dogs. Currently, prognostic and therapeutic determinations for MCTs are primarily based on the histologic grade of the tumor, but a vast majority of MCTs are of an intermediate grade, and the prognostic relevance is highly questioned. A more detailed prognostic evaluation, especially of grade 2 canine MCTs, is greatly needed. To evaluate the prognostic significance of KIT and tryptase expression patterns in canine cutaneous MCTs, we studied 100 cutaneous MCTs from 100 dogs that had been treated with surgery only. The total survival and disease-free survival time and the time to local or distant recurrence of MCTs were recorded for all dogs. Using immuno-histochemistry, 98 of these MCTs were stained with anti-KIT and antitryptase antibodies. Three KIT- and three tryptase-staining patterns were identified. The KIT-staining patterns were identified as 1) membrane-associated staining, 2) focal to stippled cytoplasmic staining with decreased membrane-associated staining, and 3) diffuse cytoplasmic staining. The tryptase-staining patterns were identified as 1) diffuse cytoplasmic staining, 2) stippled cytoplasmic staining, and 3) little to no cytoplasmic staining. Based on univariate and multivariate survival analysis, increased cytoplasmic KIT staining was significantly associated with an increased rate of local recurrence and a decreased survival rate. The tryptase-staining patterns were not significantly associated with any survival parameter. On the basis of these results, we propose a new prognostic classification of canine cutaneous MCTs, according to their KIT-staining pattern, that can be used for the routine prognostic evaluation of canine cutaneous MCTs.

Cellular Proliferation in Canine Cutaneous Mast Cell Tumors: Associations with c-KIT and Its Role in Prognostication

Canine cutaneous mast cell tumor (MCT) is a common neoplastic disease in dogs. Due to the prevalence of canine MCTs and the variable biologic behavior of this disease, accurate prognostication and a thorough understanding of MCT biology are critical for the treatment of this disease. The goals of this study were to evaluate and compare the utility of the proliferation markers Ki67, proliferating cell nuclear antigen (PCNA), and argyrophilic nucleolar organizing region (AgNOR) as independent prognostic markers for canine MCTs and to evaluate the use of these markers in combination, as each marker assesses different aspects of cellular proliferation. An additional goal of this study was to evaluate the associations between cellular proliferation and c-KIT mutations and between cellular proliferation and aberrant KIT protein localization in canine MCTs. Fifty-six MCTs treated with surgical excision alone were included in this study. Each MCT was evaluated for Ki67 expression, PCNA expression, and KIT protein localization using immunohistochemistry; for AgNOR counts using histochemical staining; and for the presence of internal tandem duplication c-KIT mutations using polymerase chain reaction amplification. In this study, increased Ki67 and AgNOR counts were both associated with significantly decreased survival. On the basis of these results, we recommend that the evaluation of cellular proliferation, including evaluations of both Ki67 expression and AgNORs, should be routinely used in the prognostication of canine MCTs. Additionally, the results of this study show that MCTs with aberrant KIT protein localization or internal tandem duplication c-KIT mutations are associated with increased cellular proliferation, further suggesting a role for c-KIT in the progression of canine MCTs.

Mutations in the Juxtamembrane Domain of c-KIT Are Associated with Higher Grade Mast Cell Tumors in Dogs

Mast cell tumors are among the most commonly seen tumors of the skin in dogs and are more highly aggressive than mast cell tumors of other species. Some breeds display a markedly higher incidence of mast cell tumor development than others and appear to have some genetic predisposition. Recently, mutations have been found in canine mast cell tumor tissues and cell lines within the juxtamembrane domain of the protooncogene c- KIT. In previous studies utilizing a small number of cases, no association between the presence of a mutation and the breed of dog or grade of the tumor could be identified. An expanded study with a larger sample set was performed to explore this possibility. The juxtamembrane domain of c- KIT was amplified using the polymerase chain reaction from genomic DNA preparations of 88 paraffin-embedded mast cell tumors from selected breeds. Mutations, consisting of duplications and deletions, were found in 12 of the tumors. A significant association was found between the presence of a mutation and a higher grade of tumor but not between breed and grade or between breed and the presence of a mutation.

Detection of c-kit Mutations in Canine Mast Cell Tumors using Fluorescent Polyacrylamide Gel Electrophoresis

Mutations consisting of internal tandem duplications (ITDs) in exons 11 and 12 of the proto-oncogene c- kit are found in 30–50% of malignant canine mast cell tumors (MCTs). Traditionally, identification of such mutations in tumor specimens has been undertaken using standard polymerase chain reaction (PCR) and agarose gel electrophoresis. This procedure is limited to the detection of insertions and deletions larger than 9 base pairs in size. The purpose of this study was to compare the efficiency and accuracy of standard agarose gel electrophoresis with fluorescent polyacrylamide gel electrophoresis (PAGE) for the detection of ITDs in canine MCTs. The results of this study demonstrate that PAGE of labeled PCR products accurately predicts the size of the ITD in each tumor. In addition, other small insertions and deletions were not identified, suggesting that if they occur in canine MCTs, they do so infrequently. Because fluorescent and polyacrylamide formats are automated and have better resolution than agarose gels, fluorescent PAGE provides a more accurate, economical, and higher throughput method for the detection of c- kit mutations in canine MCTs.

Expression of the KIT Protein (CD117) in Primary Cutaneous Mast Cell Tumors of the Dog

Thirty-one canine cutaneous masses, diagnosed as mast cell tumors (MCT) by histopathologic analysis, were used to evaluate the immunohistochemical pattern of expression of KIT protein (CD117), a type III tyrosine kinase protein involved in mast cell growth and differentiation. Lesions were graded as I (well differentiated), II (intermediate differentiation), or III (poorly differentiated) according to the following morphologic features: invasiveness, cellularity and cellular morphology, mitotic index, and stromal reaction. Immunohistochemical KIT expression was compared with histologic grade and some histomorphologic features (cell differentiation and nuclear grade) evaluated separately. A possible predictive role of biologic behavior in MCTs for KIT expression was also investigated. Immunohistochemical analysis revealed three different patterns of KIT expression: a cytoplasmic diffuse pattern, a membranous pattern with immunostaining located on the cell surface, and a cytoplasmic perinuclear pattern, where KIT expression was detected in the cytoplasm of the neoplastic mast cells, close to the nucleus. Statistical analysis showed a close relationship between different KIT immunohistochemical patterns and histologic grade ( P < 0.00000), cell differentiation ( P < 0.00000), and nuclear grade ( P < 0.0024). According to Kaplan-Meier–estimated survival curves compared by survival analysis, KIT expression was significantly associated with survival time ( P = 0.037) but not cancer-free interval ( P = 0.50). Similar to other well-known histomorphological features, KIT expression is a useful parameter of malignancy in cutaneous MCTs. KIT expression also predicted the biological behavior of the tumors in this study.

Cutaneous mastocytosis with a mutation in the juxtamembrane domain of c-kit in a young laboratory beagle dog

Cutaneous mastocytosis, which resembles a subset of urticaria pigmentosa in humans, is rare in dogs. We herein report unrepresentative neoplastic proliferation of mast cells in ventral skin removed routinely from a nine-month-old female laboratory beagle dog at necropsy. A histological examination revealed diffuse extensive cellular infiltration from the superficial to deep dermis in most parts of the skin around the fourth and fifth mammary papilla without nodule formation. Tumor cells were fairly monomorphic, well-differentiated mast cells with round nuclei of small distinct nucleoli and moderate to abundant, slightly eosinophilic and granular cytoplasm. A perivascular arrangement of mast cells was noted at the margin of the lesions. Infiltration of eosinophils and degeneration of collagen were not observed in the dermis. Cutaneous mastocytosis was diagnosed based on these features. A sequence analysis of lesions revealed the deletion of Gln₅₅₅ to Ile₅₇₀ within the juxtamembrane domain of c-kit (exon 11).

Comparative Aspects of BRAF Mutations in Canine Cancers

Activating mutations of the BRAF gene lead to constitutive activation of the MAPK pathway. The characterization and discovery of BRAF mutations in a variety of human cancers has led to the development of specific inhibitors targeting the BRAF/MAPK pathway and dramatically changed clinical outcomes in BRAF-mutant melanoma patients. Recent discovery of BRAF mutation in canine cancers underscores the importance of MAPK pathway activation as an oncogenic molecular alteration evolutionarily conserved between species. A comparative approach using the domestic dog as a spontaneous cancer model will provide new insights into the dysregulation of BRAF/MAPK pathway in carcinogenesis and facilitate in vivo studies to evaluate therapeutic strategies targeting this pathway's molecules for cancer therapy. The BRAF mutation in canine cancers may also represent a molecular marker and therapeutic target in veterinary oncology. This review article summarizes the current knowledge on BRAF mutations in human and canine cancers and discusses the potential applications of this abnormality in veterinary oncology.

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.

Biology and Diseases of Dogs

Historically, the dog played an important role as a laboratory animal in biomedical research. Although numbers are declining, the use of dogs continues to be common in pharmacokinetics and cardiovascular studies. The normal biology of the dog as both a laboratory and a companion animal has been well studied and reference values are presented here as a clinical and experimental resource. This provides the necessary background to discuss the spontaneous diseases, including infectious and neoplastic conditions, prevalent in purpose bred as well as random source dogs used in biomedical research. In addition, diseases and conditions that arise secondary to the housing and experimental manipulation of dogs is discussed with emphasis on treatment and prevention.

The Relevance of CD117-Immunocytochemistry Staining Patterns to Mutational Exon-11 in c-kit Detected by PCR from Fine-Needle Aspirated Canine Mast Cell Tumor Cells

Canine cutaneous mast cell tumors (MCT) are the lethal skin tumors. The biological behavior of the MCT cells is quite varied and unpredictable. Almost MCT dogs usually require a rapid diagnosis and therapy. However, MCT diagnosis and prognosis are still dependent on histopathology which is rather inconvenient, time-consuming, painful, and harmful for some cases. Indeed, MCT can be easily accessible using fine-needle aspiration (FNA). In this study, our biopsy specimens were classified as low- and high-grade MCT based on the novel 2-tier histopathologic grading system. We have demonstrated the usage of fine-needle aspirated MCT cells (FNA-MCT cells) from these specimens as a primary cell source to study the distribution of CD117-immunocytochemistry (CD117-ICC) staining patterns and the frequency of internal tandem duplication- (ITD-) mutant exon-11 of c-kit. The result has substantially shown that there were three staining patterns identified in the cells. Only paranuclear pattern was significantly increased in the cells from high-grade MCT. Altogether, the ITD-mutant exon-11 was also detectable only in these cells. Therefore, the result has supported our hypothesis that there was an increased opportunity to observe a higher CD117-ICC staining pattern and exon-11 mutation in high-grade MCT; even these two parameters may not precisely indicate a histopathological grade.

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.

Imatinib responsiveness in canine mast cell tumors carrying novel mutations of c-KIT exon 11

In 2 individual cases of canine mast cell tumors, we identified 2 novel c-KIT mutations in exon 11: a 9-base pair (bp) deletion (c.1663-1671del) and a point mutation (c.1676T>A). The 9-bp deletion mutation caused a loss of 3 amino acids, corresponding to p.Gln555_Lys557del, and the point mutation resulted in the substitution of valine by aspartic acid (p.Val559Asp) in the juxtamembrane domain of the protein. Imatinib mesylate, a therapeutic agent for canine mast cell tumors, was used to treat both tumors. Complete remission was achieved at 33 and 14 days after administration, respectively. However, in both cases, the therapeutic response subsequently tapered with the duration of remission lasting 66 and 255 days, respectively. Although these 2 novel c-KIT mutations in exon 11 were not confirmed to be gain-of-function mutations, a further study may help clarify relevance between mutations identified in this report and responsiveness.

Beyond H&E: integration of nucleic acid-based analyses into diagnostic pathology

Veterinary pathology of infectious, particularly viral, and neoplastic diseases has advanced significantly with the advent of newer molecular methodologies that can detect nucleic acid of infectious agents within microscopic lesions, differentiate neoplastic from nonneoplastic cells, or determine the suitability of a targeted therapy by detecting specific mutations in certain cancers. Polymerase chain reaction-based amplification of DNA or RNA and in situ hybridization are currently the most commonly used methods for nucleic acid detection. In contrast, the main methodology used for protein detection within microscopic lesions is immunohistochemistry. Other methods that allow for analysis of nucleic acids within a particular cell type or individual cells, such as laser capture microdissection, are also available in some laboratories. This review gives an overview of the factors that influence the accurate analysis of nucleic acids in formalin-fixed tissues, as well as of different approaches to detect such targets.

The use of COLD-PCR, DHPLC and GeneScanning for the highly sensitive detection of c-KIT somatic mutations in canine mast cell tumours

The conventional polymerase chain reaction (PCR)/sequencing methods may be poorly suited for the detection of somatic mutations in canine mast cell tumour (MCT) samples owing to limited sensitivity. This study was aimed at establishing novel and more sensitive methods, assessing their limit of detection and comparing their sensitivity with conventional methods.Two different 'driver' somatic mutations of c-KIT, together with the wild-type counterparts, were cloned in plasmids to prepare standard samples with known concentrations of mutated alleles in a background of wild-type alleles; the plasmids standards were assayed using either conventional or novel, highly sensitive technique. Conventional PCR/sequencing showed a sensitivity of 50-20%. Conversely, all the novel methods obtained higher sensitivities allowed reaching as low as 2.5-1.2% of the mutated DNA.The study demonstrates that early conventional methods could likely have underestimated the prevalence of KIT mutations of MCTs, therefore affecting the assessment of their relevance in prognosis and tyrosine kinase inhibitor (TKI) treatment effectiveness.

Breed-predispositions to cancer in pedigree dogs

Cancer is a common problem in dogs and although all breeds of dog and crossbred dogs may be affected, it is notable that some breeds of pedigree dogs appear to be at increased risk of certain types of cancer suggesting underlying genetic predisposition to cancer susceptibility. Although the aetiology of most cancers is likely to be multifactorial, the limited genetic diversity seen in purebred dogs facilitates genetic linkage or association studies on relatively small populations as compared to humans, and by using newly developed resources, genome-wide association studies in dog breeds are proving to be a powerful tool for unravelling complex disorders. This paper will review the literature on canine breed susceptibility to histiocytic sarcoma, osteosarcoma, haemangiosarcoma, mast cell tumours, lymphoma, melanoma, and mammary tumours including the recent advances in knowledge through molecular genetic, cytogenetic, and genome wide association studies.

NI-1: a novel canine mastocytoma model for studying drug resistance and IgER-dependent mast cell activation

BACKGROUND

Advanced mast cell (MC) disorders are characterized by uncontrolled growth of neoplastic MC in various organs, mediator-related symptoms, and a poor prognosis. Kit mutations supposedly contribute to abnormal growth and drug resistance in these patients.

METHODS

We established a novel canine mastocytoma cell line, NI-1, from a patient suffering from MC leukemia.

RESULTS

NI-1 cells were found to form mastocytoma lesions in NOD/SCID IL-2Rgamma(null) mice and to harbor several homozygous Kit mutations, including missense mutations at nucleotides 107(C→T) and 1187(A→G), a 12-bp duplication (nucleotide 1263), and a 12-bp deletion (nucleotide 1550). NI-1 cells expressed several MC differentiation antigens, including tryptase, Kit, and a functional IgE receptor. Compared to the C2 mastocytoma cell line harboring a Kit exon 11 mutation, NI-1 cells were found to be less responsive against the Kit tyrosine kinase inhibitors (TKI) masitinib and imatinib, but were even more sensitive against proliferation-inhibitory effects of the mammalian target of rapamycin (mTOR) blocker RAD001 and PI3-kinase/mTOR blocker NVP-BEZ235. The Kit-targeting multikinase inhibitors PKC412 and dasatinib were also found to override TKI resistance in NI-1 cells, and produced growth inhibition with reasonable IC(50) values (<0.1 μM).

CONCLUSION

NI-1 may serve as a useful tool to investigate IgE-dependent reactions and mechanisms of abnormal growth and drug resistance in neoplastic MC in advanced mastocytosis.

Immunohistochemical evaluation of AKT protein activation in canine mast cell tumours

The pathogenesis of canine mast cell tumour (MCT) remains unknown. Moreover, therapeutic options are limited and resistance to targeted drugs and recurrences are common, necessitating the identification of additional cellular targets for therapy. In this study we investigated the expression of phosphorylated AKT protein in 25 archival canine MCT samples by immunohistochemistry and examined the correlation between the immunohistochemical scores and histopathological tumour grades. AKT protein was detected in all of the samples and 24 of the 25 samples expressed the phosphorylated form of the protein, albeit with variable intensity. However, when the immunohistochemical scores of weak, intermediate and strong labelling were compared with the histopathological grades I to III, there was no strong correlation. This study suggests that canine MCT cells have activated AKT and indicates the need for further research on the role of the AKT protein and the possibility of targeting the AKT signalling pathway in MCTs.

Targeted knockdown of canine KIT (stem cell factor receptor) using RNA interference

Canine mast cell tumours often express KIT mutations that result in constitutive activation of the c-kit receptor and which are associated with more aggressive disease. The aim of the current study was to determine whether small inhibitory RNA (SiRNA) molecules could specifically target canine KIT mRNA for knock-down. Canine beta-2 microglobulin (B2M), glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and KIT sequences were cloned into the psiCHECK™-2 vector. SiRNA molecules, designed to target gene-specific sequences, were co-transfected with plasmid DNA into Chinese hamster ovary (CHO) cells. Renilla and firefly luciferase activity was measured using the Dual-GLO(®) Luciferase Assay (Promega). Using this reporter system, canine housekeeping gene-specific SiRNA molecules demonstrated knockdown of their targets (72.0% knockdown for B2M and 94.5% knockdown for GAPDH). An SiRNA molecule targeting exon 2 of canine KIT successfully knocked-down reporter gene expression of a KIT(26-407) construct (90.8% knockdown). An SiRNA molecule targeting a 48 base-pair in-tandem duplication mutation in KIT exon 11 selectively knocked down expression of the KIT(1569-1966mutant) construct (93.1% knockdown) but had no effect on the KIT(1569-1918wild-type) construct. The results show that RNA interference can be used to inhibit canine KIT mRNA expression and has the potential to selectively target the mutant version of KIT that is expressed by some malignant mast cells.

Canine subcutaneous mast cell tumors: cellular proliferation and KIT expression as prognostic indices

Molecular assays are widely used to prognosticate canine cutaneous mast cell tumors (MCT). There is limited information about these prognostic assays used on MCT that arise in the subcutis. The aims of this study were to evaluate the utility of KIT immunohistochemical labeling pattern, c-KIT mutational status (presence of internal tandem duplications in exon 11), and proliferation markers--including mitotic index, Ki67, and argyrophilic nucleolar organizing regions (AgNOR)--as independent prognostic markers for local recurrence and/or metastasis in canine subcutaneous MCT. A case-control design was used to analyze 60 subcutaneous MCT from 60 dogs, consisting of 24 dogs with subsequent local recurrence and 12 dogs with metastasis, as compared to dogs matched by breed, age, and sex with subcutaneous MCT that did not experience these events. Mitotic index, Ki67, the combination of Ki67 and AgNOR, and KIT cellular localization pattern were significantly associated with local recurrence and metastasis, thereby demonstrating their prognostic value for subcutaneous MCT. No internal tandem duplication mutations were detected in exon 11 of c-KIT in any tumors. Because c-KIT mutations have been demonstrated in only 20 to 30% of cutaneous MCT and primarily in tumors of higher grade, the number of subcutaneous MCT analyzed in this study may be insufficient to draw conclusions on the role c-KIT mutations in these tumors.

Canine and human gastrointestinal stromal tumors display similar mutations in c-KIT exon 11

Background

Gastrointestinal stromal tumors (GISTs) are common mesenchymal neoplasms in the gastrointestinal tract of humans and dogs. Little is known about the pathogenesis of these tumors. This study evaluated the role of c-KIT in canine GISTs; specifically, we investigated activating mutations in exons 8, 9, 11, 13, and 17 of c-KIT and exons 12, 14, and 18 of platelet-derived growth factor receptor, alpha polypeptide (PDGFRA), all of which have been implicated in human GISTs.

Methods

Seventeen canine GISTs all confirmed to be positive for KIT immunostaining were studied. Exons 8, 9, 11, 13 and 17 of c-KIT and exons 12, 14, and 18 of PDGFRA, were amplified from DNA isolated from formalin-fixed paraffin-embedded samples.

Results

Of these seventeen cases, six amplicons of exon 11 of c-KIT showed aberrant bands on gel electrophoresis. Sequencing of these amplicons revealed heterozygous in-frame deletions in six cases. The mutations include two different but overlapping six base pair deletions. Exons 8, 9, 13, and 17 of c-KIT and exons 12, 14, and 18 of PDGFRA had no abnormalities detected by electrophoresis and sequencing did not reveal any mutations, other than synonymous single nucleotide polymorphisms (SNPs) found in exon 11 of c-KIT and exons 12 and 14 of PDGFRA.

Conclusions

The deletion mutations detected in canine GISTs are similar to those previously found in the juxtamembrane domain of c-KIT in canine cutaneous mast cell tumors in our laboratory as well as to those reported in human GISTs. Interestingly, none of the other c-KIT or PDGFRA exons showed any abnormalities in our cases. This finding underlines the critical importance of c-KIT in the pathophysiology of canine GISTs. The expression of KIT and the identification of these activating mutations in c-KIT implicate KIT in the pathogenesis of these tumors. Our results indicate that mutations in c-KIT may be of prognostic significance and that targeting KIT may be a rational approach to treatment of these malignant tumors. This study further demonstrates that spontaneously occurring canine GISTs share molecular features with human GISTs and are an appropriate model for human GISTs.