Mast cells and canine mast cell tumours. A review

This article reviews the literature on mast cells and tumours derived from mast cells in the dog. Mast cells play a central role in inflammatory and immune reactions. Mast cells, normal and neoplastic, contain and release important biologically active substances: heparin, histamine, eosinophilic chemotactic factor and proteolytic enzymes. Mast cell tumours occur in the dog, particularly in the boxer and related breeds, in the skin and less frequently in the intestines. Cytology usually provides an accurate diagnosis, but histological examination adds further information concerning the histologic grade and the completeness of surgical therapy. Cutaneous mast cell tumours should be regarded as potentially malignant and therefore be removed widely (3 cm. margin). Local recurrence, regional and distant metastases together with paraneoplastic disorders may cause the death of the pet. Histologic grading (2 or 3 grades) and clinical staging together with kinetic parameters and breed (boxers have relatively benign tumours) are important prognostic parameters. Based on prognostic criteria, surgical treatment should be completed with adjuvant radiotherapy, corticosteroids and eventually with combined chemotherapy. A novel, promising therapy is the application of the receptor kinase inhibitor. The study of the pathogenesis of mast cell tumours received new impetus by the finding of mutations, deletions and duplications, in exons 11 and 12 of the C-kit oncogene. Further study of physiological and oncological aspects of mast cells are favoured by the availability of mast cells isolated from spontaneous mast cell tumours and of cultured cell lines.     

Splenic mast cell tumour and mastocytaemia in a cat: case study and literature review

Case: An 11-year-old female domestic shorthaired cat presenting with clinical signs of depression, anorexia, weight loss, fever, anaemia and a mid-abdominal mass was referred for abdominal ultrasound examination.

Clinical findings: Ultrasonography of the abdomen identified a markedly enlarged spleen. Ultrasound-guided fine- needle aspiration biopsy of the spleen revealed a uniform population of mast cells, 11% of which were observed to have phagocytosed erythrocytes. It is speculated that this may have been a contributing factor in the development of anaemia in this case. Mast cells were detected in a peripheral-blood smear and a diagnosis of systemic mastocytosis (splenic mast cell tumour together with mastocytaemia) was made. This diagnosis was subsequently confirmed by histopathology of the spleen.

Conclusion: Splenectomy and treatment with corticosteroids appears to have resulted in remission of clinical signs and anaemia. A reduction in the concentration of mast cells in the peripheral blood had not occurred 6 weeks post- splenectomy, but was evident by 10 months post-splenectomy.     

Multivariate Survival Analysis of Histological Parameters and Clinical Presentation in Canine Cutaneous Mast Cell Tumours

The Patnaik histological grade is a good method for the prediction of long-term mast cell tumour behaviour but it is influenced by subjective inter-observer variations and intratumoral heterogeneity. The present study evaluated each of the histopathological parameters used to formulate Patnaik’s grade in terms of prognosis and tested whether they have a different prognostic sensitivity, thereby disclosing which could be considered more useful in the prediction of tumour recurrence and patient survival. Clinical presentation (single or multiple tumours) was also considered as possible prognostic factor. The results demonstrated that individual histological criteria together with multiple presentation may be of value in predicting the outcome of mast cell tumours. Among these, invasiveness (β1.85; standard error 1.15) and the number of mitotic figures (β3.01; standard error 1.18) showed high prognostic significance (Cox proportional hazard regression for censored data ; chi-squared = 15.52, degree of freedom = 6, p = 0.016) and could serve as reliable prognostic indicators avoiding more subjective parameters such as cellular differentiation, nuclear morphology and tumoural pattern. R. Preziosi Deceased     

Association of prognostic features and treatment on survival time of dogs with systemic mastocytosis: A retrospective analysis of 40 dogs

Systemic mastocytosis is a rare phenomenon, with limited information regarding prognostic features and effective treatment of canine patients with this disease. The objective of this study is to determine the impact of certain features and treatments on dogs with systemic mastocytosis. The medical records of 40 dogs from 4 northeastern US veterinary hospitals, with evidence of systemic mast cell disease, were evaluated retrospectively. Variables analysed with relation to overall survival and prognostic significance included treatment protocol used, substage, presence of a cutaneous or visceral tumour, presence of multiple cutaneous Mast cell tumours, grade of the primary tumour and metastatic site(s). Dogs with metastatic disease confined to distant lymph nodes lived longer than those with circulating mast cells in the blood (P = .001), and those with metastatic disease evident in more than 2 sites had a worse prognosis than those with disease in a single location (P = .005). Additionally, administration of chemotherapeutic agents led to increased survival over prednisone therapy alone (P = .008), with the combination of lomustine, vinblastine and prednisone prolonging survival over the tyrosine kinase inhibitor, toceranib phosphate (P = .002). Presence of mast cells in the blood and/or evidence of disease in more than 2 sites indicate widespread dissemination suggesting their use as negative prognostic features. Furthermore, a chemotherapy protocol including combination lomustine and vinblastine therapy may be more effective than toceranib phosphate for the treatment of dogs with disseminated mast cell disease. Overall, patients with systemic mastocytosis have a grave prognosis and more effective treatment options are needed.     

Assessment of proliferative activity of canine dermal mast cells by bromodeoxyuridine and proliferating cell nuclear antigen labelling

Cutaneous mast cells from skin biopsies of three healthy dogs and three dogs with atopic dermatitis were assessed for their proliferative potential using bromodeoxyuridine and proliferating cell nuclear antigen labelling. Mast cells isolated from the skin of two healthy dogs were also studied using bromodeoxyuridine labelling. Mast cells in skin biopsy specimens and mast cells isolated from the skin of healthy dogs did not incorporate bromodeoxyuridine. Two mast cells expressing proliferating cell nuclear antigen were seen around two superficial vessels in the dermis of one atopic dog. Epidermal cells, glandular epithelial cells, fibroblasts and endothelial cells incorporated bromodeoxyuridine and showed positive staining for proliferating cell nuclear antigen. These results suggest that canine mature mast cells do not proliferate in the dermis.     

Reduced mucosal injury of SPF chickens by mast cell stabilization after infection with very virulent infectious bursal disease virus

Recent studies here have demonstrated that increased mast cell populations and tryptase activity contribute to lesion formation in regions of immune organs in special-pathogen-free chickens after infection with very virulent infectious bursal disease virus (vvIBDV). Mast cells and their mediators have been implicated in acute inflammatory injury after vvIBDV infection, but their precise role in this process remains elusive. In this study, the role of mast cells in the vvIBDV infection process was examined using ketotifen, a mast cell membrane stabilizer. On days 1, 2, and 3 postinfection, the bursa of Fabricius (BFs) were collected to quantify mast cells, tryptase and histamine contents by cytochemistry, immunohistochemistry and fluorospectrophotometry analyses, respectively. The results showed that the mast cell populations, tryptase expression, and histamine released increased significantly in the BFs (p < 0.01) of infected birds compared to controls, and acute inflammatory responses were observed in the former. In contrast, in infected chickens pretreated with ketotifen, mast cells, tryptase, and histamine were markedly decreased (p < 0.01) and probably as a result, the BFs remitted significantly. The overall results suggest that mast cells are positively involved in BF injury induced by vvIBDV infection. Inhibition of mast cell degranulation and concurrent mediator release may represent a novel strategy to modulate this process. This study, thus, advances the understanding of the acute inflammatory injury mechanisms triggered by vvIBDV infection and the contribution of mast cell activity in this process.     

Canine Transmissible Venereal Tumour: Asessment of Mast Cell Numbers as Indicators of the Growth Phase

Mast cells are immune cells that are involved mainly in type 1 hypersensitivity reactions, and they have been implicated in tumour angiogenesis. In this study we assessed the presence of mast cell numbers and microvessel density during the progression and regression stages of natural spontaneous canine transmissible venereal tumours (CTVT). Mast cells were demonstrated by histochemical staining with toluidine blue, alcian blue and safranin O. Microvessel counts were demonstrated by immunohistochemical labelling with an antibody against the endothelial cell marker factor VIII. Mitotic cells, apoptotic cells and tumour infiltrating lymphocytes were counted from haematoxylin–eosin-stained sections. Tumour fibrosis was evaluated on Masson's trichome-stained sections. The results showed that progressing tumours had significantly higher mast cell counts and microvessel counts at the invasive edges of the tumours than did regressing tumours. In both the progressing and regressing tumours, microvessel counts were significantly positively correlated with mast cell counts. Regressing tumours had significantly higher mast cell counts of the whole tumour than progressing tumours. The results also showed that progressing tumours had significantly higher mitotic rate than regressing tumours, and fibrosis and apoptosis were significantly higher in regressing tumours than progressing tumours. There were no significant differences between the biochemical and haematological values of dogs with progressing and regressing tumours. These results suggests that mast cells play a role in CTVT progression probably by promoting vascularization at the invasion front during the progression phase, and that mast cell count could be used as one of the histological factors to indicate growth stage of CTVT.     

Heterogeneity of internal tandem duplications in the c‐kit of dogs with multiple mast cell tumours

Mast cell tumours are one of the most common neoplasms in dogs. Mutations in the proto‐oncogene c‐kit, especially internal tandem duplications of exon 11, are considered to play a crucial role in mast cell tumourigenesis. In this report, two cases that suffered from multiple mast cell tumours containing an internal tandem duplication in the primary lesion but not in the secondary lesions are described. This finding indicates the existence of heterogenous c‐kit gene mutations in each site of multiple mast cell tumours. Additionally, these results raise the possibility that the contribution of internal tandem duplications in the malignant transformation of mast cells is quite limited. It is proposed that, for clinicians, genetic analysis of several regions of multiple mast cell tumours is necessary for predicting prognosis and tumour response to KIT inhibitors.     

Results of adrenalectomy in 36 dogs with hyperadrenocorticism caused by adrenocortical tumour

Summary

A total of 38 adrenocortical tumours were removed from 36 dogs with hyperadrenocorticism. The surgical approach was by way of a unilateral flank laparotomy (32 dogs; 14 left and 18 right), a bilateral flank laparotomy (3 dogs) or a midline celiotomy (1 dog).

Two dogs were euthanized during surgery because their tumours could not be resected. Eight dogs died from post‐operative complications. Pancreatic necrosis with peritonitis was the most common cause of death. Eight of the 26 dogs that survived had signs of recurrence of hyperadrenocorticism. Unsuppressible hyperadrenocorticism was found in four dogs; one dog had probably pre‐existent pituitary‐dependent hyperadrenocorticism, and adrenocortical function could not be re‐examined in the remaining three dogs.

Among the 37 tumours examined microscopically expansion of neoplastic tissue into blood vessels was found in 22 of them. Four adrenal glands with adrenocortical tumours also contained phaeochromocytomas. Necropsy was performed in eight dogs. Metastases were found in the lungs of two dogs and in the lungs and liver in one dog.

In combination with the data of previous reports, it is suggested that histological findings in surgery specimens are not good predictors for the clinical outcome.     

Mast cell tumour and cutaneous histiocytoma excision wound healing in general practice

Objective : To assess whether wounds from incomplete mast cell tumour excisions are at greater risk of healing complications than wounds from complete excisions, or cutaneous histiocytomas. Methods : Mast cell tumours and cutaneous histiocytomas submitted to Nationwide Laboratories between November 1, 2007 and April 30, 2008 were selected. Questionnaires were sent to submitting veterinarians requesting details of tumour characteristics, clinical approach to the tumour and wound healing. Results : Three hundred and eighty‐six mast cell tumours and 524 cutaneous histiocytomas were identified. One hundred and eighty‐five mast cell tumours and 244 cutaneous histiocytomas questionnaires were returned (47% response). Wound complications arose in 20% of mast cell tumours and 21% of cutaneous histiocytomas. Multivariable analysis confirmed that larger tumours, tumours on the feet and a soft/“baggy” appearance, were significantly associated with a greater frequency of problems, leading to delayed wound healing and dehiscence. Clinical Significance : Incomplete mast cell tumour excision does not lead to greater risk of wound complications. Mast cell tumour surgical wounds have a similar rate of wound complications as cutaneous histiocytoma wounds.     

Production of stem cell factor in canine mast cell tumors

Mast cell tumor (MCT) is the most common cutaneous tumor in dogs. We recently revealed that production of stem cell factor (SCF) contributes to the proliferation of neoplastic mast cells in an autocrine/paracrine manner. The aim of the present study was to determine the contribution of the mechanism in clinical MCTs. In consequence, high SCF expression (>10 times compared to HRMC cells) was observed in 5 of 7 MCT samples used in the study regardless of KIT mutation, which was confirmed in immunohistochemical analysis. In addition, production of SCF was observed in Ki-67-positive cells in the MCT xenograft. These results indicate the broad contribution of SCF autocrine/paracrine mechanism on clinical MCTs, providing the rationale for the clinical use of KIT inhibitors regardless of KIT mutation.     

Urinary and faecal N-methylhistamine concentrations do not serve as markers for mast cell activation or clinical disease activity in dogs with chronic enteropathies

Background

This study sought to correlate faecal and urinary N-methylhistamine (NMH) concentrations with resting versus degranulated duodenal mast cell numbers in dogs with chronic enteropathies (CE), and investigate correlations between intestinal mast cell activation and clinical severity of disease as assessed by canine chronic enteropathy clinical activity index (CCECAI), and between urinary and faecal NMH concentrations, mast cell numbers, and histopathological scores. Twenty-eight dogs with CE were included. Duodenal biopsies were stained with haematoxylin and eosin (H&E), toluidine blue, and by immunohistochemical labelling for tryptase. Duodenal biopsies were assigned a histopathological severity score, and duodenal mast cell numbers were counted in five high-power fields after metachromatic and immunohistochemical staining. Faecal and urinary NMH concentrations were measured by gas chromatography–mass spectrometry.

Results

There was no correlation between the CCECAI and faecal or urinary NMH concentrations, mast cell numbers, or histopathological score – or between faecal or urinary NMH concentration and mast cell numbers. Post hoc analysis revealed a statistically significant difference in toluidine blue positive mast cells between two treatment groups (exclusion diet with/without metronidazole versus immunosuppression (IS)), with higher numbers among dogs not requiring IS.

Conclusion

Faecal and urinary NMH concentrations and duodenal mast cell numbers were not useful indicators of severity of disease as assessed by the CCECAI or histological evaluation. The number of duodenal mast cells was higher in dogs that did not need IS, i.e. in dogs responding to an exclusion diet (with/without metronidazole), than in dogs requiring IS. Further studies comparing the role of mast cells in dogs with different forms of CE are needed.     

High lysyl oxidase expression is an indicator of poor prognosis in dogs with cutaneous mast cell tumours

Mast cell tumour (MCT) is one of the most frequent skin tumours in dogs. Due to their unpredictable biological behaviour, MCTs often cause several therapeutic frustrations, leading to investigation regarding prognostic markers. Lysyl oxidase (LOX) is an enzyme that promotes extracellular matrix stability and contributes to cell migration, angiogenesis and epithelial-mesenchymal transition. Its expression positively correlates with poor prognoses in several human and canine mammary cancers. The aim of this study was to characterise the immunohistochemical expression of LOX in MCT samples and compare it with histological grading and post-surgical survival. Twenty-six tumours were submitted to immunohistochemistry for LOX expression evaluation. All samples were positive for LOX, with variable percentages of cytoplasmic and nuclear positivity. Cytoplasmic positivity was significantly higher in high-grade MCTs (P = .0297). Our results indicate that high expression of cytoplasmic LOX in neoplastic mast cells is an indicator of poor prognosis for canine cutaneous MCTs.     

A Study of the Number and Distribution of Cutaneous Mast Cells in Cats with Disease not Affecting the Skin

Resumen— El propósito de este estudio era investigar el número de mastocitos dérmicos en diferentes partes de la piel de gatos con enfermedad que no afecta a la piel. Se hizo un recuento de el número de mastocitos en 10 partes diferentes de la piel de 12 gatos sin evidencia de enfermedad de la piel. Se fijaron muestras de biopsia de piel en fijador Carnoy y formalina neutral atenuada, y se tiñeron con azul touluidina. Se realizaron recuentos de celulas de 6 campos de alto poder (400), de cada parte. Los recuentos de mastocitos combinados para todos los gatos, todas las partes y ambos fijadores variaban de 0–60 con un promedio de 12.5 por campo de alto poder y eran mas altos en el aspecto caudal del pabellón auricular y en la barbilla. El tipo de fijador usado no pareció influir en el recuento de mastocitos. [Foster, A. P. A study of the number and distribution of cutaneous mast cells in cats with diseases not affecting the skin (Un estudio de el número y distribución de mastocitos cutaneos en gatos con enfermedad que no afecta a la piel).
Abstract— The purpose of this study was to investigate the number of dermal mast cells in different skin sites from cats with disease not affecting the skin. The number of mast cells in the skin of 12 cats without evidence of skin disease was counted from 10 different skin sites. Skin biopsy samples were fixed in Carnoy's fixative and neutral buffered formalin and stained with toluidine blue. Cell counts from 6 high power fields (400) were made for each site. Mast cell counts combined for all cats, all sites and both fixatives ranged from 0 to 60 with a mean of 12.5 per high power field and were highest from the caudal aspect of the pinna and the chin. The type of fixative used did not appear to influence mast cell counts.     

Multinodular Malignant Cutaneous Mast Cell Tumor in a Horse With Generalized Pruritus and Reactive Fibrosis: A Case Report

Mast cell tumor (MCT) has long been considered as an uncommon neoplasm in horses. Cytological and behavioral evidence of its malignancy is usually lacking, and only a few reports have described MCT displaying malignant behavior. An 18-year-old Friesian stallion presented with a one-year history of intermittent and progressive skin lesions on the left forelimb associated with intense, generalized pruritus and apathy temporarily responsive to glucocorticoids and antibiotics. The horse was alert and responsive with poor body condition and marked generalized pruritus. The left forelimb was markedly enlarged and surrounded by numerous firm 2- to 20-cm masses that were ulcerated and focally necrotic. A 7-cm round firm mass was observed on the left dorsal neck. Dermatological examination revealed generalized moth-eaten alopecia and scaling with erosions and ulcers secondary to pruritus. A direct skin smear from the affected leg showed severe eosinophilic inflammation and neutrophilic inflammation with pleomorphic bacteria. Histopathology of the skin and biopsies of the underlying tissues revealed an abundant population of atypical mast cells consistent with a malignant MCT. The horse was euthanized and necropsy revealed a marked fibrous reaction on longitudinal sections of the affected limb, and the tumor could be detected on only a few histological slides. Diagnosis of equine MCT can be challenging because of the massive accompanying fibrous reaction. Mast cell tumor should be suspected in the presence of eosinophilic infiltration of the affected tissue and in cases of generalized pruritus not attributable to other causes.     

<Emphasis Type="Italic">In vitro</Emphasis> chemosensitivity of canine mast cell tumors grades II and III to all-<Emphasis Type="Italic">trans</Emphasis>-retinoic acid (ATRA).

Mast cell tumor (MCT) is one of the most prevalent neoplasms that affect the skin and soft tissue of dogs. Because mast cell tumors present a great variety of clinical appearance and behavior, their treatment becomes a challenge. While retinoids are well recognized as promising antitumor agents, there have been only a few reports about retinoids’ effect on canine cancers. The aim of this study was to investigate the chemosensitivity of MCT grades II and III to all-trans retinoic acid (ATRA). Immediately after surgical resection, MCT were prepared for primary culture. Samples of MCTs were also fixed in formalin for histopathology and grading according to the classification of Patnaik et al. (Veterinary Pathology 21(5):469–474, 1984). The best results were obtained when neoplastic mast cells were co-cultivated with fibroblasts. Cultured mast cells were, then, treated with concentrations of 10⁻⁴ to 10⁻⁷ M of ATRA, in order to evaluate their chemosensitivity to this retinoid. MTT assay was performed to estimate cell growth and death. The highest level of mast cell chemosensivity was obtained at the dose of 10⁻⁴ M (p < 0,002). MCT of grades II or III were equally susceptible to the treatment with ATRA. Cell death was observed on the first 24 h until 48 h. According to these results, ATRA may be a potential chemotherapeutic agent for the treatment of canine MCT.     

Marked subcutaneous mast cell and eosinophilic infiltration associated with the presence of multiple Dirofilaria repens microfilariae in 4 dogs

Dirofilaria repens is a parasitic nematode in the subcutaneous tissue of carnivores, including dogs and cats, transmitted by mosquitoes. Human beings may be accidental hosts. Infection of a dog with D repens was first reported in Palestine in 1934, and 2 additional cases were reported in dogs in Israel to date. This report describes D repens infection in 4 dogs in Israel that presented with subcutaneous masses, which were cytologically characterized by marked mast cell and eosinophil infiltration. In 3 cases, multiple microfilariae were present in the lesions; rare microfilariae were present in the 4^th case. In all 4 dogs, PCR of fine‐needle aspirates from the lesions were positive for D repens. The mast cells observed in all lesions were uniform and highly granulated, and with the presence of the microfilariae, a mast cell tumor was considered less likely. This report suggests that D repens infection‐associated subcutaneous lesions, characterized cytologically by massive mast cell and eosinophil infiltration, should be considered a differential diagnosis for mast cell tumor, especially in geographic locations endemic for this nematode. Notably, all 4 dogs were infected with D repens despite a routine prophylactic doramectin therapy administered every 3 months, probably due to the relatively long time interval between treatments.     

Precursor‐targeted immune‐mediated anemia in a dog with a stage IV mast cell tumor and bone marrow infiltration

A 12‐year‐old spayed female Shiba Inu dog was referred to our hospital for a suspected mast cell tumor (MCT) of the bone marrow (BM). Laboratory abnormalities included severe nonregenerative anemia (packed cell volume or PCV: 12.5%; reference interval (RI): 37.3‐61.7%; reticulocytes: 35.1 × 10³/µL; RI: 10‐110 × 10³/µL), and a few mast cells were visualized in the blood smear examination. The BM was hypercellular with hematopoietic cells, a decreased myeloid:erythroid (M:E) ratio (0.77; RI, 0.9‐1.8), and no dysplastic hematopoietic cells. Mast cells accounted for 11.5% of the total nucleated BM cells. Neoplastic mast cells and histiocytes phagocytizing erythroid progenitor cells were occasionally noted. The dog was diagnosed with precursor‐targeted immune‐mediated anemia (PIMA) concurrent and a stage IV MCT infiltrating the BM. Multimodal treatment included toceranib, imatinib, vinblastine, lomustine (CCNU), prednisolone, cyclosporine, mycophenolate mofetil, and a blood transfusion. The dog died due to MCT progression lasting 139 days after the initial BM examination. To the best of our knowledge, this is the first report of a dog presenting with PIMA and a stage IV MCT infiltrating the BM.     

Ultrasonographic findings in abdominal mast cell disease: a retrospective study of 19 patients

A retrospective survey from January 1989 to January 1999 of Tufts University Foster Hospital for Small Animals radiology records of 12 dogs and seven cats with cytologically or histopathologically confirmed abdominal mast cell disease was performed. Ultrasound changes in hepatic mast cell infiltration in dogs included a subjective increase in size, a diffuse increase in echogenicity, and one or more hypoechoic nodules. Ultrasound findings in the affected canine spleen included one or more hypoechoic nodules and a subjective increase in size. Two ultrasonographically unremarkable canine livers and one unremarkable spleen were found to be infiltrated by mast cells. The mast cell-infiltrated feline spleen was subjectively increased in size, mottled, irregular, or contained nodules. The affected lymph nodes in both dogs and cats were hypoechoic or inhomogeneous, subjectively increased in size, and rounded. Gastrointestinal involvement in cats was characterized by a thickened ileocecocolic junction or colon with loss of wall layering. Mast cells were not found in the gastrointestinal tract in any dog. One dog with mast cell infiltrate of the kidneys had multiple hypoechoic nodules in the cortex that distorted the outer contour of the kidney. Although these findings are not specific to the disease in either species, abdominal ultrasound is considered a useful tool for determining the extent of disease in small-animal patients with mast cell tumor if used in conjunction with histopathology or cytology.