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

Investigation of the Theragnostic Role of KIT Expression for the Treatment of Canine Mast Cell Tumors with Tyrosine Kinase Inhibitors

Several reports have indicated that canine MCTs express a mutated form of a tyrosine kinase receptor, namely KIT, that is involved in abnormal mast cell growth and differentiation. Currently, the post-surgical prognosis for MCTs is related to three different KIT immunohistochemical expression patterns. However, to our knowledge, there are few studies specifically exploring the efficacy of treatment with tyrosine kinase inhibitors related to KIT staining pattern. The purpose of this study was to investigate the potential theragnostic role of KIT expression patterns by studying their correlation to the overall survival and progression-free survival in dogs treated with only tyrosine kinase inhibitors immediately after surgery. We selected 66 cases of canine cutaneous MCTs with complete clinical background. A statistical analysis was performed to assess the overall survival status. Our data suggest an important role of KIT in the etiopathogenesis of canine MCTs and indicate that the anomalous cytoplasmatic distribution of KIT is potentially related to a lower efficacy of tyrosine kinase inhibitors, thus providing a significant prognostic information about the treatment outcome.

Cutaneous Canine Mast Cell Tumor: The Use of Proliferative Markers (Ki-67 and Ki-67 × AgNOR) in Cytological Samples for Diagnosis and Prognosis

A cytological grading system for canine mast cell tumors (MCTs) has been developed, but its integration into clinical routine has been hindered due to its diagnostic limitations. The aim of this study was to assess the prognostic value of Ki-67 and argyrophilic nucleolar organizing region (AgNOR) markers in cytological MCT samples and to determine cut-off values for these markers in correlation with histopathological grading. Cytological samples were collected prior to surgical excision, and histopathological samples were obtained postsurgery from 45 dogs diagnosed with cutaneous mast cell tumors (MCTs). The cytological specimens were classified using a two-tier grading system, and their Ki-67 (average immunopositive nuclei per 100 cells) and AgNOR (average AgNOR counts per 100 nuclei) signaling was assessed. Through receiver operating characteristic (ROC) analysis, cut-off values for Ki-67 and Ki-67 × AgNOR were determined to better align with histopathological grading (classified as low or high grade according to Kiupel's scoring system). Without the inclusion of proliferative markers, there was a 73% agreement between cytological and histopathological grading. The prediction of histopathological grade was slightly more accurate when assessing Ki-67 and Ki-67 × AgNOR signaling in cytological specimens (75% and 80%, respectively) compared to the initial cytological grading. The cytological assessment of canine MCTs proves beneficial for the initial evaluation, and the incorporation of the evaluation of Ki-67 and AgNOR markers may assist in identifying diagnostically highly malignant MCTs.

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.

Human C1q Tumor Necrosis Factor 8 (CTRP8) defines a novel tryptase+ mast cell subpopulation in the prostate cancer microenvironment

The adipokine C1q Tumor Necrosis Factor 8 (CTRP8) is the least known member of the 15 CTRP proteins and a ligand of the relaxin receptor RXFP1. We previously demonstrated the ability of the CTRP8-RXFP1 interaction to promote motility, matrix invasion, and drug resistance. The lack of specific tools to detect CTRP8 protein severely limits our knowledge on CTRP8 biological functions in normal and tumor tissues. Here, we have generated and characterized the first specific antiserum to human CTRP8 which identified CTRP8 as a novel marker of tryptase+ mast cells (MC_T) in normal human tissues and in the prostate cancer (PC) microenvironment. Using human PC tissue microarrays composed of neoplastic and corresponding tumor-adjacent prostate tissues, we have identified a significantly higher number of CTRP8+ MC_T in the peritumor versus intratumor compartment of PC tissues of Gleason scores 6 and 7. Higher numbers of CTRP8+ MC_T correlated with the clinical parameter of biochemical recurrence. We showed that the human MC line ROSA^{KIT WT} expressed RXFP1 transcripts and responded to CTRP8 treatment with a small but significant increase in cell proliferation. Like the cognate RXFP1 ligand RLN-2 and the small molecule RXFP1 agonist ML-290, CTRP8 reduced degranulation of ROSA^{KIT WT} MC stimulated by the Ca²⁺-ionophore A14187. In conclusion, this is the first report to identify the RXFP1 agonist CTRP8 as a novel marker of MC_T and autocrine/paracrine oncogenic factor within the PC microenvironment.

Preliminary Assessment of Tumor-Associated Tissue Eosinophilia (TATE) in Canine Mast Cell Tumors: Prevalence and Prognostic Relevance and Its Association with Neoangiogenesis

Mast cell tumor (MCT) is the most common malignant skin tumor in dogs. In order to gain more information on the prognostic markers in MCT, the role of the eosinophil granulocytes infiltrates was investigated and assessed by the evaluation of tumor-associated tissue eosinophilia (TATE) in 87 canine cutaneous MCTs. In human medicine, high TATE are often described in highly angiogenic tumors: we therefore assessed the vascular endothelial growth factor (VEGF) expression in neoplastic mast cells. TATE and VEGF expression were compared between themselves, with histological grading, immunohistochemical expression of KIT and Ki-67, and with the recurrence. We found a statistically significant correlation between TATE and Patnaik grading (p = 0.041), Kiupel grading (p = 0.022), immunohistochemical KIT expression (p = 0.015), and tumor recurrence (p = 0.000). No associations were observed with Ki-67 and VEGF expression. This is the first evaluation of TATE and its prognostic value in canine MCTs in veterinary oncology. This study suggest that this investigation could be an important source of information for this tumor and for other neoplasms.

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.

Imatinib Mesylate for the Treatment of Canine Mast Cell Tumors: Assessment of the Response and Adverse Events in Comparison with the Conventional Therapy with Vinblastine and Prednisone

Mast cell tumors (MCTs) are common neoplasms in dogs, and treatments for these diseases include surgery, polychemotherapy and targeted therapy with tyrosine kinase inhibitors. This study aimed to evaluate the response and the adverse events of treatment with imatinib mesylate (IM) compared to conventional therapy using vinblastine and prednisolone (VP) in canine cutaneous MCTs. Twenty-four dogs were included in the study; 13 animals were treated with IM and 11 with VP. Tumor tissue samples were submitted for histological diagnosis, grading and KIT immunostaining. The response to treatment was assessed by tomographic measurements according to VCOG criteria. Adverse events were classified according to VCOG-CTCAE criteria. The IM and VP groups had dogs with similar breeds, gender, ages, MCT localization, WHO stages and lymph node metastasis profiles. Most MCTs were grade 2/low and had KIT- patterns 2 and 3. The objective response rate (ORR) was significantly higher (30.79%) in the IM group then in VP group (9.09%). Adverse events (AE) in IM group were all grade 1, significantly different from VP. In conclusion, IM presented better ORR and less severe adverse events when compared to VP, representing a suitable option for the treatment of low-grade canine MCTs.

Proposed Diagnostic Criteria and Classification of Canine Mast Cell Neoplasms: A Consensus Proposal

Mast cell neoplasms are one of the most frequently diagnosed malignancies in dogs. The clinical picture, course, and prognosis vary substantially among patients, depending on the anatomic site, grade and stage of the disease. The most frequently involved organ is the skin, followed by hematopoietic organs (lymph nodes, spleen, liver, and bone marrow) and mucosal sites of the oral cavity and the gastrointestinal tract. In cutaneous mast cell tumors, several grading and staging systems have been introduced. However, no comprehensive classification and no widely accepted diagnostic criteria have been proposed to date. To address these open issues and points we organized a Working Conference on canine mast cell neoplasms in Vienna in 2019. The outcomes of this meeting are summarized in this article. The proposed classification includes cutaneous mast cell tumors and their sub-variants defined by grading- and staging results, mucosal mast cell tumors, extracutaneous/extramucosal mast cell tumors without skin involvement, and mast cell leukemia (MCL). For each of these entities, diagnostic criteria are proposed. Moreover, we have refined grading and staging criteria for mast cell neoplasms in dogs based on consensus discussion. The criteria and classification proposed in this article should greatly facilitate diagnostic evaluation and prognostication in dogs with mast cell neoplasms and should thereby support management of these patients in daily practice and the conduct of clinical trials.

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.

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

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

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.

Canine and Feline Cutaneous Mast Cell Tumor: A Comprehensive Review of Treatments and Outcomes

Mast cell tumor (MCT) or mastocytoma is one of the most frequent malignant cutaneous tumors in the dog, and the second most frequent in the cat. Several mast cell tumor therapeutic approaches have been proposed in the past years for dogs and cats, resulting in very distinct outcomes. The current comprehensive literature review presents a critical approach to the scientific information published about the MCTs treatments and the subsequent prognosis and survival times, in dogs and in cats diagnosed with MCTs. A systematic review of the literature following the Cochrane principles and methodology was performed. The authors resorted to MEDLINE, Scopus, Google Scholar and Web of Science databases to select the 133 publications with evidence-based treatments for MCTs in companion animals. Results of the review suggest that the recommended treatment, prognosis and survival times for dogs and cats with MCTs depends at all times on the clinical staging, histological grade and location of the tumor.

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.

Canine CD117-Specific Antibodies with Diverse Binding Properties Isolated from a Phage Display Library Using Cell-Based Biopanning

CD117 (c-Kit) is a tyrosine kinase receptor that is overexpressed in multiple dog tumors. There is 100% homology between the juxtamembrane domain of human and canine CD117, and many cancer-causing mutations occur in this region in both species. Thus, CD117 is an important target for cancer treatment in dogs and for comparative oncology studies. Currently, there is no monoclonal antibody (mAb) specifically designed to target the exposed region of canine CD117, although there exist some with species cross-reactivity. We panned a naïve phage display library to isolate antibodies against recombinant CD117 on whole cells. Several mAbs were isolated and were shown to bind recombinant canine CD117 at low- to sub-nanomolar affinity. Additionally, binding to native canine CD117 was confirmed by immunohistochemistry and by flow cytometry. Competitive binding assays also identified mAbs that competed with the CD117 receptor-specific ligand, the stem cell factor (SCF). These results show the ability of our cell-based biopanning strategy to isolate a panel of antibodies that have varied characteristics when used in different binding assays. These in vitro/ex vivo assessments suggest that some of the isolated mAbs might be promising candidates for targeting overexpressed CD117 in canine cancers for different useful applications.

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.

Canine cutaneous mast cell tumors: A combined clinical and pathologic approach to diagnosis, prognosis, and treatment selection

In view of the varied biologic behavior and the costs of treatment for canine cutaneous mast cell tumors, development of appropriate treatment plans for individual affected dogs can be difficult, but decisions regarding treatment should be made using a systematic, evidence-based approach. This manuscript reviews the current state of diagnostics and prognostication of canine cutaneous mast cell tumors, and suggests a combined approach based on clinical and pathologic assessment for decision making regarding treatment choices. The current state of histologic grading, evaluation of proliferation indices, evaluation of mutations in the c-kit gene and KIT expression, evaluation of excision and clinical staging are examined. On the basis of the current understanding of prognostication and treatment response, algorithms for selection of local and systemic therapy are presented.

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.

CD117 expression influences proliferation but not survival in canine mammary tumours

CD117 is a transmembrane tyrosine kinase receptor encoded by the c-Kit proto-oncogene. The immunohistochemical expression of CD117 was examined in 49 specimens of canine mammary glands (eight normal/hyperplastic, 11 benign tumours and 30 malignant tumours). Expression was assessed as: (1) presence or absence of CD117; (2) membrane, cytoplasmic, or both, distributions; and (3) percentage of CD117-labelled cells. None of these three immunohistochemical parameters was correlated with the type of mammary tissue (i.e. normal, benign or malignant), histotypes or histological stage of malignant tumours, or survival. An association was observed between Ki67 index and all three CD117 labelling parameters only for malignant tumours, with a significant increase in proliferative activity in tumours expressing CD117, mainly with both cytoplasmic and membrane expression.

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.

The value of molecular expression of KIT and KIT ligand analysed using real-time polymerase chain reaction and immunohistochemistry as a prognostic indicator for canine cutaneous mast cell tumours

This study investigated the correlation between KIT gene expression determined by immunohistochemistry and real-time polymerase chain reaction (RT-PCR) and the rate of tumour recurrence and tumour-related deaths in dogs affected with mast cell tumour (MCT). Kaplan-Meier curves were constructed to compare tumour recurrence and tumour-related death between patients. The log-rank test was used to check for significant differences between curves. KIT-I, KIT-II and KIT-III staining patterns were observed in 9 (11.11%), 50 (61.73%) and 22 (27.16%) tumours, respectively. Tumour recurrence rates and tumour-related deaths were not associated with KIT staining patterns (P = 0278, P > 0.05), KIT (P = 0.289, P > 0.05) or KIT ligand (P = 0.106, P > 0.05) gene expression. Despite the lack of association between KIT staining pattern and patient survival time, the results suggest a correlation between aberrant KIT localization and increased proliferative activity of MCTs. RT-PCR seems to be a sensible method for quantitative detection of KIT gene expression in canine MCT, although expressions levels are not correlated with prognosis.

Biological behavior of oral and perioral mast cell tumors in dogs: 44 cases (1996-2006)

OBJECTIVE

To describe clinical outcome of dogs with mast cell tumors (MCTs) arising from the oral mucosa, oral mucocutaneous junction, or perioral region of the muzzle and evaluate the potential role of the chemokine receptor type 7 (CCR7) in the biological behavior of these tumors.

DESIGN

Retrospective case series.

ANIMALS

44 dogs with MCTs of the oral mucosa (n=14), oral mucocutaneous junction (19), or perioral region of the muzzle (11).

PROCEDURES

Medical records were reviewed for information on signalment, regional metastasis, treatments, cause of death, and survival time. Twenty of the 44 cases had stored histologic samples available for immunohistochemical staining for CCR7

RESULTS

For all dogs, median survival time was 52 months. Twenty-six (59%) dogs had regional lymph node metastasis on admission. Median survival time for dogs with lymph node metastasis was 14 months, whereas median survival time was not reached for dogs without lymph node metastasis. Intensity of staining for CCR7 was not significantly associated with the presence of regional lymph node metastasis or survival time.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that in dogs with MCTs arising from the oral mucosa, oral mucocutaneous junction, or perioral region of the muzzle, the presence of regional lymph node metastasis at the time of diagnosis was a negative prognostic factor. However, prolonged survival times could be achieved with treatment. In addition, CCR7 expression in the primary tumor was not significantly associated with the presence of regional lymph node metastasis or survival time.

Prognostic value of histologic and immunohistochemical features in feline cutaneous mast cell tumors

Feline cutaneous mast cell tumors (MCTs) have been histologically classified as mastocytic (well differentiated or pleomorphic) and atypical/poorly granulated. Their biologic behavior ranges from benign to malignant, but prognostic factors are not well defined. Histologic classification, number of tumors, mitotic index, cytoplasmic granularity, and infiltration by eosinophils or lymphocytes were evaluated retrospectively in 25 feline cutaneous MCTs. Immunohistochemistry was applied to assess KIT (CD117) pattern and immunoreactivity score, telomerase expression (human telomerase reverse transcriptase), and proliferation index (MIB-1/Ki67 index). Case outcome was obtained via telephone interviews. The tumors comprised 15 mastocytic well-differentiated, 7 mastocytic pleomorphic, and 3 atypical/poorly granulated MCTs. Immunohistochemically, CD117 was expressed in 13 of 25 tumors (52%), and telomerase reverse transcriptase was expressed in 15 of 22 (68%), with no correlation to histologic classification. Mitotic index, KIT immunoreactivity score, and Ki67 index were significantly higher in mastocytic pleomorphic MCTs than in the other 2 categories. Five cats (20%) died of tumor-related causes. Multiplicity of lesions, pleomorphic phenotype, KIT immunoreactivity score, and mitotic and Ki67-indices correlated with an unfavorable outcome. Mitotic index was the strongest predictive variable. These results suggest that histologic classification, CD117/KIT immunohistochemistry, and proliferation indices may help to identify potentially aggressive cases of feline cutaneous MCT. Aberrant KIT protein localization and telomerase immunoreactivity warrant further exploration as potential prognostic markers.

Immunohistochemical expression of the KIT protein (CD117) in normal and neoplastic canine testes

The aim of the present study was to characterize the expression of the KIT protein (CD117) in normal and neoplastic canine testes. Archival samples of normal testis (n=5), interstitial cell tumours (ICTs; n=10), Sertoli cell tumours (SCTs; n=10) and seminomas (n=10) were selected. Seminomas were subclassified on the basis of expression of placental alkaline phosphatase (PLAP) as classical seminoma (SE; PLAP positive; n=5) or spermatocytic seminoma (SS; PLAP negative; n=5). In normal testes, KIT expression was observed in Leydig cells and in spermatogonia. All ICTs expressed KIT, but no SCT was positively labelled. Seven of 10 seminomas expressed KIT and these tumours were reclassified on this basis as SS (KIT negative) or SE (KIT positive). These findings are consistent with observations of SE in man where many of the neoplastic cells reach the stage of spermatogonia where PLAP expression is lost and that of KIT is maintained. It would therefore appear that immunolabelling for KIT expression is a more appropriate means of distinguishing between canine SE and SS.

Expression of KIT Receptor in Feline Cutaneous Mast Cell Tumors

Twenty-seven feline cutaneous mast cell tumors (MCTs) were selected for this retrospective study. Samples were routinely processed and stained with hematoxylin and eosin (HE) and toluidine blue, and tumors were classified as well-differentiated (19/27), atypical or poorly granulate (7/27), and pleomorphic (1/27). Immunohistochemistry to detect KIT protein was performed on all samples. The immunoreactivity was recorded by distribution within the tumor, cellular location, and intensity. Well-differentiated MCTs were predominantly characterized by diffuse cytoplasmic (8/19) and membranous stain (7/19); a diffuse distribution of KIT positive cells was displayed in most of these tumors as well (15/19). Atypical MCTs showed diffuse distribution of labeled cells (4/7), and diffuse cytoplasm immunostaining was seen most (5/7). The pleomorphic MCT showed diffuse cytoplasmic KIT stain, with moderate labeling intensity, typically displaying focal distribution in deeper areas of the neoplasm. According to the results, there was no correlation between the type of MCTs and KIT expression, although the use of feline KIT immunohistochemistry could be useful to assess the mast cell origin.

Canine subcutaneous mast cell tumour: diagnosis and prognosis

The aim of this study was to characterize the pathology and clinical outcome of the subcutaneous variant of canine mast cell tumour. Fifty-three cases satisfying the inclusion criteria were selected from the pathology archive of the College of Veterinary Medicine, University of Tennessee. Referring veterinarians provided information on outcome. These dogs had a median age of 9 years (range 3-17 years). After characterizing tumours histologically, nuclear expression of proliferating cell nuclear antigen (PCNA) and Ki67 (MIB-1 clone) was determined immunohistochemically and mast cell origin was confirmed with c-Kit staining. Counts of argyrophilic nucleolar organizer regions (AgNOR) were determined by silver staining. Nuclear labelling was counted in 100 tumour cells. Margins were recorded as incomplete in 66% of dogs, and metastases occurred in 6% of dogs. The estimated minimum mean survival time from date of diagnosis was 1199 days, ranging from 55 to >1780 days. The median scores from immunohistochemical labelling were PCNA 0.05 and Ki67 0.03 per 100 tumour cells. The median score for AgNOR staining was 1.25 per 100 tumour cells. The patterns of c-Kit expression included membranous labelling in 20 tumours, stippled cytoplasmic labelling in 23 tumours and diffuse cytoplasmic labelling in 10 tumours. Age (r=-0.61, P=0.14) and AgNOR score (r=-0.58, P=0.17) had moderate, but non-significant, negative associations with survival. PCNA (r=-0.32, P=0.47), Ki67 (r=-0.22, P=0.64) and c-Kit immunolabelling was not associated with survival. The subcutaneous variant of canine mast cell tumour is distinct in having features of intermediate histological grade and extended mean survival times, suggesting a slightly better long-term prognosis than for higher grade dermal variants. Expression of nuclear proliferation markers is not associated with outcome.

Expression of c-kit proto-oncogene in canine mastocytoma: a kinetic study using real-time polymerase chain reaction

KIT receptor, the c-kit gene product, is thought to play a major role in canine mastocytoma, one of the most common neoplastic diseases in dogs. In the present study, the expression of c-kit proto-oncogene in blood and in tumor biopsies from 41 dogs with histologically confirmed mastocytoma at different grades of cellular differentiation and 5 negative control dogs was investigated using real-time (quantitative) reverse transcription-polymerase chain reaction (RRT-PCR). The animals were followed up for over 1 year after surgery in order to characterize the kinetics of c-kit expression in blood. Transcript mRNAs extracted from blood at different time points after surgery and from tumor tissue surgically removed from each dog were used in a quantitative RRT-PCR assay targeting the extracellular coding region of the c-kit gene. Tissues constitutively expressing c-kit (brain and spleen) were used as positive controls. Levels of expression of c-kit were higher in tumor biopsies than in blood; the blood level decreased in the patients between 1 and 3 months after surgery. No KIT expression was detected in blood from the 5 dogs not affected by mastocytoma (negative controls). The RRT-PCR appears to be a suitable method for sensitive and quantitative detection of c-kit gene expression in canine blood and neoplastic tissues. Although c-kit expression levels measured by RRT-PCR do not correlate with prognosis, they confirm that surgery remains the main treatment to reduce circulating mastocytes and that circulating mast cells can be detected even in benign highly differentiated forms of mastocytoma such as grade I.

The role of c-KIT in tumorigenesis: evaluation in canine cutaneous mast cell tumors

The c-KIT proto-oncogene has been implicated in the pathogenesis of several neoplastic diseases, including gastrointestinal stromal tumors and mastocytosis in humans, and mast cell tumors (MCTs) in canines. Cutaneous MCTs are common neoplasms in dogs and have a variable biologic behavior. The goal of this study was to define the prognostic significance of c-KIT mutations identified in canine MCTs and the associations between c-KIT mutations, KIT localization, and KIT expression levels. Microdissection and polymerase chain reaction were performed on 60 MCTs to identify c-KIT mutations. Anti-KIT antibodies were used for immunohistochemical evaluation of KIT localization. Forty-two MCTs were included in a tissue microarray, and KIT expression was quantified using immunofluorescence. Canine MCTs with c-KIT mutations were significantly associated with an increased incidence of recurrent disease and death. c-KIT mutations were also significantly associated with aberrant protein localization; however, the level of KIT expression did not correlate with either c-KIT mutations or changes in protein localization. Considering the high prevalence of canine MCTs and the central role of c-KIT in the tumorigenesis of certain tumors, canine MCTs are an excellent model for characterizing the role of c-KIT in neoplastic diseases and is a potential target for novel therapeutic agents in clinical trials.

Evaluation of the kinase domain of c-KIT in canine cutaneous mast cell tumors

BACKGROUND

Mutations in the c-KIT proto-oncogene have been implicated in the progression of several neoplastic diseases, including gastrointestinal stromal tumors and mastocytosis in humans, and cutaneous mast cell tumors (MCTs) in canines. Mutations in human mastocytosis patients primarily occur in c-KIT exon 17, which encodes a portion of its kinase domain. In contrast, deletions and internal tandem duplication (ITD) mutations are found in the juxtamembrane domain of c-KIT in approximately 15% of canine MCTs. In addition, ITD c-KIT mutations are significantly associated with aberrant KIT protein localization in canine MCTs. However, some canine MCTs have aberrant KIT localization but lack ITD c-KIT mutations, suggesting that other mutations or other factors may be responsible for aberrant KIT localization in these tumors.

METHODS

In order to characterize the prevalence of mutations in the phospho-transferase portion of c-KIT's kinase domain in canine MCTs exons 16-20 of 33 canine MCTs from 33 dogs were amplified and sequenced. Additionally, in order to determine if mutations in c-KIT exon 17 are responsible for aberrant KIT localization in MCTs that lack juxtamembrane domain c-KIT mutations, c-KIT exon 17 was amplified and sequenced from 18 canine MCTs that showed an aberrant KIT localization pattern but did not have ITD c-KIT mutations.

RESULTS

No mutations or polymorphisms were identified in exons 16-20 of any of the MCTs examined.

CONCLUSION

In conclusion, mutations in the phospho-transferase portion of c-KIT's kinase domain do not play an important role in the progression of canine cutaneous MCTs, or in the aberrant localization of KIT in canine MCTs.