Hepatic Mastocytosis in Japanese Black Cattle.

In 5 Japanese Black steers (2-2.4 years old) that originated from 5 different feedlots, the livers were found at slaughter to have multiple nodular or cordlike lesions (5 steers) and an extensive fibrotic area (1 steer). Microscopic changes included extensive fibroplasia in the portal tracts and chronic proliferative endophlebitis-like lesions confined to the portal vein branches. Fibroplasia was much more prominent in the macroscopic fibrotic lesion of 1 steer. Portal vein branches presented irregular variciform dilation of the vascular lumen and fibroplastic changes in the subendothelial areas that showed occasional hemorrhage and were simultaneously infiltrated with large numbers of mast cells and moderate to large numbers of eosinophils. Within these subendothelial regions, not only did mast cells exhibit cytologically atypical features, but they also formed multifocal nodules. The venous lesions may represent a variant of mastocytosis with specific involvement of the hepatic portal vein branches in cattle.

Pilot study utilizing Fluorine-18 fluorodeoxyglucose-positron emission tomography/computed tomography for glycolytic phenotyping of canine mast cell tumors.

The goal of this prospective pilot study was to use naturally occurring canine mast cell tumors of various grades and stages as a model for attempting to determine how glucose uptake and markers of biologic behavior are correlated. It was hypothesized that enhanced glucose uptake, as measured by 2-[fluorine-18]fluoro-d-glucose-positron emission tomography/computed tomography (F18 FDG PET-CT), would correlate with histologic grade. Dogs were recruited for this study from a population referred for treatment of cytologically or histologically confirmed mast cell tumors. Patients were staged utilizing standard of care methods (abdominal ultrasound and three view thoracic radiographs), followed by a whole body F18 FDG PET-CT. Results of the F18 FDG PET-CT were analyzed for possible metastasis and standard uptake value maximum (SUVmax ) of identified lesions. Incisional or excisional biopsies of the accessible mast cell tumors were obtained and histology performed. Results were then analyzed to look for a possible correlation between the grade of mast cell tumors and SUVmax . A total of nine animals were included in the sample. Findings indicated that there was a correlation between grade of mast cell tumors and SUVmax as determined by F18 FDG PET-CT (p-value = 0.073, significance ≤ 0.1). Based on the limited power of this study, it is felt that further research to examine the relationship between glucose utilization and biologic aggressiveness in canine mast cell tumors is warranted. This study was unable to show that F18 FDG PET-CT was a better staging tool than standard of care methods.

Feline Epitheliotropic Mastocytic Conjunctivitis in 15 Cats.

Mast cell infiltration occurs in malignant, inflammatory (eg, allergic, infectious), and idiopathic disease processes in humans and animals. Here, we describe the clinical and histological features of a unique proliferative conjunctivitis occurring in 15 cats. Ocular specimens were examined histologically, and polymerase chain reaction (PCR) for feline herpesvirus 1 (FHV-1) was performed on ocular tissues obtained from 10 cats. Cats had a median age of 8 years (range: 7 months-17.5 years). The known median duration of ocular lesions prior to biopsy was 4 months (range: 1 week-3 years). Ocular disease was unilateral in 12 cats, and 9 cats had coexisting corneal disease. Clinically and histologically, proliferative or nodular conjunctival lesions were noted in 13 cats. The nictitating membrane was affected in 10 cats. Histologically, lesions were characterized by mixed inflammatory infiltrates with an abundance of Giemsa-positive and toluidine blue-positive intraepithelial and subepithelial mast cells, marked edema, and papillary epithelial hyperplasia. Feline herpesvirus 1 was demonstrated by PCR in 1 of 10 cats tested. Follow-up information was available for 14 cats: 8 had no recurrence during a median follow-up period of 17.5 months (range: 4.5-30 months), 2 underwent orbital exenteration, 3 had recurrence that was medically managed, and 1 cat had diffuse conjunctivitis at the time of biopsy and recurrence was deemed irrelevant. Various ocular medications were administered before and after surgical biopsy. This condition was designated as feline epitheliotropic mastocytic conjunctivitis, with intraepithelial mast cells being an essential feature and papillary epithelial proliferation being characteristic but not diagnostic alone. The condition appears to be uncommon and benign. Although the cause is unknown, an allergic component is possible.

Skin depigmentation associated with toceranib phosphate in a dog.

BACKGROUND: Drug-induced depigmentation is frequently observed in humans undergoing tyrosine kinase inhibitor therapy, whereas it is not reported in dogs. The skin depigmentation can occur after the first week of treatment and it is reversible within a few weeks after drug discontinuation. OBJECTIVES: To report the clinical and histopathological features of an episode of cutaneous adverse drug reaction associated with short term administration of toceranib phosphate. CASE REPORT: An 11-year-old intact male Bernese mountain dog was presented for investigation of a subcutaneous mast cell tumour (MCT) including treatment options. The major abnormality on physical examination was a 7.5 × 10 cm subcutaneous mass located cranial to the left shoulder joint consistent with a MCT. Toceranib phosphate therapy was initiated. Fourteen days after initiating treatment, the dog presented with skin erosions near the lateral canthus of the left eye. Three weeks later there were multiple skin lesions characterized by alopecia and depigmentation involving left and right eyelids; leukotrichia of the periorbital areas and depigmentation of the nasal planum and all paw pads. Histopathological findings were nonspecific; they were supportive of vitiligo. Resolution of skin lesions was observed after stopping the toceranib phosphate therapy. CONCLUSION AND CLINICAL IMPORTANCE: Based on the gross lesions, histopathological features before and after tyrosine kinase inhibitor therapy, and Naranjo score, this case was considered to be consistent with cutaneous adverse drug effects. To the best of the authors' knowledge, this is the first report describing the clinical and histopathological features of presumed drug-induced skin depigmentation in a dog receiving toceranib phosphate.

Influence of treatment on the outcome of dogs with incompletely excised grade-2 mast cell tumors.

INTRODUCTION: In this study we compared the outcomes of dogs with incompletely-excised grade-2 mast cell tumors (incompletely- excised grade-2 MCTs) either adjuvantly treated or not. Dogs with a grade-2 mast cell tumour (MCT) excised either incompletely or with narrow (<5mm) margins, without local recurrence or metastasis at the time of presentation and with a minimum follow-up of 10 months were included in the study. Dogs were separated in 2 groups: treatment (surgery, radiation therapy, chemotherapy or combination of those) and no-treatment. The original excision was incomplete in 90 dogs and narrow in 25 dogs. Ninety-two cases (80%) were treated and 23 (20%) were not treated, but only monitored. Pathology after revision excision found no signs of residual disease in 47/56 cases (84%). Local recurrence was confirmed in 7 dogs, suspected but not confirmed in 2 dogs. Metastatic disease was confirmed in 13 dogs and suspected but not confirmed in 11 dogs. Forty-six dogs died and 69 were still alive at the time of data collection. The 1-yr and 2-yr survival rates were 92% and 82%, respectively. No statistical differences were found regarding disease-free intervals, survival times, recurrence rates, metastatic rates, 1-year and 2-year survival rates between groups, or depending on treatment modality within the treatment group. Based on the finding that the outcome of incompletely-excised grade-2 MCTs was unaffected by adjuvant treatments, this study suggests that immediate systematic adjuvant treatment of incompletely-excised grade-2 MCTs may not be recommended over attentive monitoring and action upon uncommon recurrence.

Dans la présente étude, on compare le devenir de chiens présentant des mastocytomes de grade 2 incomplètement excisés, selon qu'ils ont reçu un traitement adjuvant ou qu'ils aient simplement été sous surveillance. On a pris en compte des chiens chez lesquels des mastocytes de grade 2 ont été incomplètement excisés ou l'ont été avec une marge étroite (<5mm) et qui ne présentaient pas de signe de récidive locale ou de métastases au moment de l'examen avec un suivi de minimum 10 mois. Les chiens ont été classés en deux groupes, l'un avec des traitements (chimiothérapie, radiothérapie, chirurgie ou combinaison de ces traitements) et l'autre sans autre traitement. L'excision originelle était incomplète chez 90 chiens et présentait des marges étroites chez 25 chiens. 92 cas (80%) ont reçu un traitement et 23 (20%) ont été surveillés sans traitement. Les résultats de l'histologie après une excision de révision n'ont pas fait état de signes d'une affection tumorale restante dans 47/56 cas (84%). Une récidive locale a été confirmée chez 7 chiens et supposée mais pas confirmée chez 2 chiens. Des métastases ont été confirmées chez 13 chiens, supposées mais non confirmées chez 11. Au moment du relevé des données, 46 chiens étaient décédés et 69 encore en vie. Le taux de survie à 1 respectivement à 2 ans était de 92% respectivement 82%. Il n'y avait pas de différence statistiquement significative entre les deux groupes en ce qui concerne les intervalles entre les affections, la durée de la survie, le taux de récidive, le taux de métastases, le taux de survie à 1 et à 2 ans ou entre les divers traitements dans le groupe des animaux traités. Les résultats de cette étude montrent que des traitements adjuvants n'influencent pas le résultat en présence de mastocytes de degré 2 incomplètement excisés. Un traitement adjuvant systématique lors de mastocytes de degré 2 incomplètement excisés ne peut donc pas être recommandé par rapport à une surveillance attentive et un traitement lors de récidive diagnostiquée.

Unilateral intraocular mastocytosis and anterior uveitis in a dog with subcutaneous mast cell tumors.

A 9-year-old male castrated Scottish terrier was referred to the Radiation Oncology Service at the William R. Pritchard Veterinary Medical Teaching Hospital for palliative radiation therapy of an incompletely excised, recurrent subcutaneous mast cell tumor (MCT) located over the right scapula, and surgical removal of a perianal MCT. Three weeks after initial presentation and prior to the fifth radiation treatment, the patient was presented with cloudiness of the left eye of 3-7 days duration. Ophthalmic consultation revealed 3+ aqueous flare with a dependent, swirling component filling approximately one-third of the anterior chamber. Aqueocentesis was performed under general anesthesia. Cytology revealed mast cells with highly atypical morphology and considered most consistent with neoplasia. The patient died 7 months after pathologic diagnosis of MCT on the right shoulder and 2 months after the cytologic diagnosis of malignant mast cells in the left anterior chamber. To the authors' knowledge, this is the first report of intraocular involvement in a mammal with MCTs, described here as intraocular mastocytosis.

Mastocytosis in the skin in dogs: A multicentric case series.

Canine cutaneous mastocytosis (CM) is rare in contrast to canine mast cell tumours. In humans, CM commonly affects children and is usually indolent with possible spontaneous resolution. Systemic mastocytosis (SM) with bone marrow involvement typically affects adults, can have a poor outcome, and often includes skin lesions. 'Mastocytosis in the skin' (MIS) is the preferred term of skin lesions, if bone marrow evaluations are not available, which is often the cases in dogs. In human SM and CM, KIT mutations are often detected. The veterinary literature suggests clinical resemblances between human and canine MIS, but data is limited, and KIT mutations are rarely assessed. This retrospective study describes clinicopathological findings, treatment and outcome of 11 dogs with suspected MIS. Dogs with multiple mast cell tumours were excluded. Histopathology reports (n = 5) or slides (n = 6) were reviewed. KIT mutation analysis including exons 8, 9, 11, 14 and 17 were analysed in eight dogs. Median age at diagnosis was 4 years (range, 1-12). Typical clinical signs included multifocal to generalised nodules and papules. Histologically, skin lesions were characterised by dermal infiltration of well-differentiated mast cells. KIT mutations were detected in 3/8 dogs (exon 9: n = 2; exon 11: n = 1). One dog had mastocytaemia suggesting possible SM. Glucocorticoids were mostly successful with lesion improvement in all treated dogs (n = 8). This cohort highlights resemblances between human and canine MIS. Further studies are required to confirm these findings and establish diagnostic criteria for CM and MIS associated with SM in dogs.

Cutaneous mast cell tumor with epitheliotropism in 3 dogs.

Epitheliotropism is an important diagnostic feature of cutaneous epitheliotropic lymphoma and canine cutaneous histiocytoma; however, although noted in certain feline mastocytic diseases, it has not been considered a feature of canine cutaneous mast cell tumor. In this study, 3 canine cutaneous mast cell tumors had epitheliotropic invasion of neoplastic mast cells into the epidermis and follicular epithelium. This unusual histologic finding was characterized by infiltrates of individual and clusters of neoplastic mast cells in the stratum basale and stratum spinosum. The mast cell origin of these cells was documented by demonstration of metachromasia with Giemsa stain and positive immunoreactivity to KIT protein. On the basis of these findings, mast cell tumors should be included in the differential diagnosis for canine cutaneous round cell neoplasms that infiltrate the epidermis.

Immunohistochemical characterization of feline mast cell tumors.

Expression of histamine, serotonin, and KIT was evaluated in 61 archived feline mast cell tumors (MCTs) from the skin (n = 29), spleen (n = 17), and gastrointestinal (GI) tract (n = 15) using immunohistochemistry. Twenty-eight percent of cutaneous MCTs, 18% of splenic MCTs, and 53% of GI MCTs displayed histamine immunoreactivity. Serotonin immunoreactivity was detected in 3 GI and 1 cutaneous MCT. Sixty-nine percent of cutaneous MCTs, 35% of splenic MCTs, and 33% of GI MCTs were positive for KIT. Expression of these biogenic amines and KIT was less common than expected. Results of this study suggest heterogeneity in feline MCTs based on anatomic location. Further studies are needed to explain the significance of these differences.

Cutaneous mast cell tumor and mastocytosis in a black-masked lovebird (Agapornis personata).

A 12-year-old female black-masked lovebird (Agapornis personata) with a cobalt color mutation was presented for self-mutilation of a mass located on the right lateral neck. Cytologic evaluation of the soft tissue mass revealed a predominance of poorly stained mast cells with metachromatic intracytoplasmic granules. The presumptive diagnosis was cutaneous mast cell tumor. Clinical evaluation, results of a complete blood cell count and biochemical analysis, and radiographs did not reveal systemic manifestation of mast cell disease. The mass was surgically resected, but surgical margins were limited because of the location of the mass and the small size of the patient. The lovebird died the day after surgery. Gross postmortem examination revealed splenomegaly, multifocal pinpoint white nodules throughout the liver parenchyma, severe thickening and yellow coloration of the great vessels, and pale pink swelling of the caudal right kidney. Histopathologic analysis of the resected mass revealed sheets of round cells that contain metachromatic granules, defined as neoplastic mast cells, within a fine fibrovascular stroma. Similar neoplastic cells were seen in the right kidney, hepatic sinusoids, splenic pulp, periovarian connective tissue, and bone marrow. The histopathologic diagnosis was a cutaneous mast cell tumor and disseminated mast cell disease, or mastocytosis. To the authors' knowledge, this is the first reported case of a cutaneous mast cell tumor and mastocytosis in a psittacine bird.

Cutaneous and splenic mastocytosis in a juvenile Malayan tiger.

A male Malayan tiger cub developed well-circumscribed, erythematous, alopecic lesions on the face, torso, and paws when 1-wk-old. Biopsies of a torso lesion and a right front paw lesion at 1-mo-old confirmed cutaneous mast cell tumors (MCTs). MCTs on the paws grew into pendulous masses up to 6.5 cm in diameter by 3-mo-old, but those on the face and torso regressed. Fine-needle aspiration of the spleen at 3-mo-old revealed marked mast cell infiltration. The spleen and the right paw cutaneous MCT were removed; the paw MCT recurred within 7 d. A 12-bp tandem duplication, suggesting a somatic mutation, was identified in exon 8 of c-KIT in DNA extracted from the cutaneous MCT on the right paw and from one over the torso, but not from the spleen. Remaining MCTs on the paws regressed slowly following splenectomy and had completely regressed by 1-y-old. At 7-y-old, there was no recurrence of any mast cell disease. Mast cell disease in this tiger cub is similar to a report in a domestic kitten and to pediatric mastocytosis in humans, which commonly begins in infancy, improves by adolescence, and is associated with somatic c-kit mutations. To our knowledge, mastocytosis has not been reported previously in a juvenile exotic felid.

Mutations in the fifth immunoglobulin-like domain of kit are common and potentially sensitive to imatinib mesylate in feline mast cell tumours.

The purpose of the current study was to investigate the mutation status of KIT in feline mast cell tumours (MCTs) and to examine the effects of tyrosine kinase inhibition on the phosphorylation of mutant kit in vitro and in clinical cases of cats. Sequence analysis of KIT identified mutations in 42/62 MCTs (67.7%). The vast majority of the mutations were distributed in exons 8 and 9, both of which encode the fifth immunoglobulin-like domain (IgD) of kit. All five types of kit with a mutation in the fifth IgD were then expressed in 293 cells and examined for phosphorylation status. The mutant kit proteins showed ligand-independent phosphorylation. The tyrosine kinase inhibitor imatinib mesylate suppressed the phosphorylation of these mutant kit proteins in transfectant cells. In a clinical study of 10 cats with MCTs, beneficial response to imatinib mesylate was observed in 7/8 cats that had a mutation in the fifth IgD of kit in tumour cells. Mutations in the fifth IgD of kit thus appear to be common and potentially sensitive to imatinib mesylate in feline MCTs. These data provide an in vivo model for paediatric mastocytosis where mutations in the fifth IgD of kit also occur.

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.

Systemic mastocytosis and probable mast cell leukaemia in a koala (Phascolarctos cinereus).

BACKGROUND: To the authors' knowledge, this is the first report of mast cell neoplasia in a koala (Phascolarctos cinereus). CASE REPORT: An adult female koala was presented for rapidly deteriorating health and death of a pouch young. Significant weight loss was apparent despite supplemental feeding; the abdomen was distended; and the koala was weak and mentally depressed. Haematology revealed a significant mastocytosis with a concurrent population of atypical mononuclear cells. The koala was euthanised and tissues were collected for histology. Bone marrow, lymph node, lung, stomach and spleen exhibited significant infiltration by mast cells. Atypical round cells consistent with those identified in the peripheral blood were also identified in the marrow. A diagnosis of systemic mastocytosis and probable mast cell leukaemia was made. Immunocytochemical and immunohistochemical staining was not able to further characterise the atypical cell population, and the mast cells exhibited only weak staining with CD117. CONCLUSION: The histological diagnosis, in this case, was systemic mastocytosis and myeloproliferative disease of uncertain origin. There was a dominant population of mast cells in the peripheral blood and marrow, and a population of circulating atypical mononuclear cells, appearing similar to mast cell leukaemia-acute myeloid leukaemia in humans.

Adjuvant medical therapy provides no therapeutic benefit in the treatment of dogs with low-grade mast cell tumours and early nodal metastasis undergoing surgery.

Lymph node (LN) metastasis is a negative prognostic factor in dogs with cutaneous mast cell tumours (cMCTs). While elective lymphadenectomy of metastatic LNs improves outcome, the benefit of adjuvant medical therapy in dogs with early metastatic (HN2) LNs is debated. The aim of this retrospective multicentre study was to evaluate the therapeutic benefit of adjuvant medical therapy following surgical removal of the primary low-grade cMCT (Patnaik grade 1-2 and Kiupel low-grade) and lymphadenectomy of HN2 LNs by analysing survival rates and patterns of recurrence. Seventy-three dogs were included: 42 received adjuvant medical treatment (chemotherapy and/or kinase inhibitors), and 31 did not. The median follow-up time for medically treated dogs was 619 days: two experienced local recurrence, three nodal relapse and four distant relapse. For dogs undergoing surgery only, the median follow-up time was 545 days. None of them experienced local recurrence, nodal, or distant relapse. Time to progression was significantly shorter in dogs receiving adjuvant medical treatment (P = .021). A similar tendency was observed for overall survival (P = .056). The current study shows that dogs with low-grade cMCTs, that undergo surgical excision of the primary tumour and elective lymphadenectomy of the HN2 regional LN harbour a good prognosis. The use of adjuvant medical treatment in these dogs does not seem to provide any benefit in terms of progression and survival.

Ultrasound is a poor predictor of early or overt liver or spleen metastasis in dogs with high-risk mast cell tumours.

Conflicting evidence exists regarding the importance of routine abdominal ultrasound (US) with hepatic and splenic fine needle aspiration (FNA) cytology during staging of canine mast cell tumours (MCT). The objective of this study was to correlate ultrasonographic and cytologic findings in dogs with strictly defined high-risk MCTs and to determine the influence on outcome. Our hypothesis was that US poorly predicts visceral metastasis in high-risk MCTs and that early metastasis is associated with improved outcome when compared to overt metastasis. US of liver and spleen correlated to cytologic results, categorized as no metastasis, early metastasis or overt metastasis. Of 82 dogs prospectively enrolled, 18% had early visceral metastasis and 7% had overt metastasis on cytology; 67% with visceral metastasis had regional LN metastasis. US was a poor predictor of metastasis with sensitivity, specificity, positive predictive value and negative predictive value for the spleen of 67%, 68%, 21% and 94%, respectively and for the liver of 29%, 93%, 56% and 82%, respectively. Median time to progression (TTP) for dogs with no metastasis, early metastasis and overt metastasis was not reached, 305 and 69 days, respectively (P < .001). Median survival time (MST) for the 3 groups were not reached, 322 and 81 days, respectively (P < .001). High Patnaik or Kiupel grade, early metastasis, overt metastasis and adequate local control were significantly associated with outcome. Early visceral metastasis was associated with poorer outcome compared to dogs without metastasis, however, a subset of dogs experienced long-term control.

VEGF concentration from plasma-activated platelets rich correlates with microvascular density and grading in canine mast cell tumour spontaneous model.

Canine cutaneous mast cell tumour (CMCT) is a common cutaneous tumour in dog, with a higher incidence than in human. CMCT is classified in three subgroups, well and intermediately differentiated (G1 and G2), corresponding to a benign disease, and poorly differentiated (G3), corresponding to a malignant disease, which metastasize to lymph nodes, liver, spleen and bone marrow. In this study, we have evaluated serum (S), platelet-poor plasma (P-PP), plasma-activated platelet rich (P-APR) and cytosol vascular endothelial growth factor (VEGF) concentrations, microvascular density (MVD) and mast cell density (MCD) in a series of 86 CMCTs and we have correlated these parameters with each other, by means of ELISA detection of VEGF and immunohistochemistry. Results show that VEGF level from cytosol P-APR and MVD were significantly higher in G3 CMCTs as compared to G1 or G2 subgroups. Moreover, a significantly strong correlation among VEGF levels from P-PAR and cytosol, MVD and MCD was found in G3 subgroup. Because VEGF levels from P-APR well correlated with MVD and malignancy grade in CMCT, we suggest that VEGF might be secreted from MCs and it may be a suitable surrogate inter-species angiogenetic markers of tumour progression in CMCT. Finally, CMCT seems to be a useful model to study the role of MCs in tumour angiogenesis and inhibition of MCs degranulation or activation might be a new anti-angiogenic strategy worthy to further investigations.

Gain-of-function mutations in the extracellular domain of KIT are common in canine mast cell tumors.

In the current study, we examined the types and frequency of KIT mutations in mast cell tumors from 191 dogs. Sequencing of reverse transcription-PCR products revealed alterations in 50 (26.2%) of the dogs. Most mutations were in exon 11 (n = 32), and of these, most were internal tandem duplications (n = 25) between residues 571 and 590. Within exon 11, there were two hotspots for mutations at codons 555-559 and 571-590. In addition, nine dogs had mutations in exon 8 and eight had mutations in exon 9. We selected the two most common mutants and two representative exon 11 mutants for further analysis. When expressed in Ba/F3 cells, they were constitutively tyrosine phosphorylated and induced growth factor-independent cell proliferation. AG1296, a tyrosine kinase inhibitor, dose dependently inhibited both the tyrosine phosphorylation of these mutants and their induction of growth factor-independent proliferation. This study shows that activating mutations in not only exon 11 but also exons 8 and 9 are common in canine mast cell tumors. These results also show that Ba/F3 cells can be used for the direct characterization of canine KIT mutants, eliminating the need to make equivalent mutations in the mouse or human genes.

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.

Disseminated cutaneous mast cell tumors with epitheliotropism and systemic mastocytosis in a domestic cat.

A 15-year-old female domestic, medium-haired cat presented to the referring veterinarian with a 2-month history of multiple, raised, disseminated, nodular skin lesions. A biopsy of 1 of the lesions was submitted to the Oklahoma Animal Disease Diagnostic Laboratory for evaluation. Histologically, there were multiple dermal nodules composed of sheets of neoplastic round cells. Multifocally, the neoplastic cells formed multiple small clusters of 3 to 5 cells within the epidermis. Distinct cytoplasmic granules were evident within the neoplastic cells with toluidine blue and Giemsa stains. The neoplastic cells were immunoreactive for c-KIT and lacked immunoreactivity for cluster of differentiation 3 with immunohistochemistry. Based on these findings, multiple epitheliotropic cutaneous mast cell tumors were diagnosed. The cat's health declined rapidly despite aggressive treatment, and the animal was humanely euthanatized. A complete necropsy revealed sheets of similar neoplastic mast cells within the spleen, liver, and individual cells scattered within the bone marrow. Exon 11 of the c-KIT messenger RNA from 1 of the cutaneous masses and the spleen was amplified with reverse transcription polymerase chain reaction, sequenced, and compared with the published c-KIT messenger RNA sequence from fetal cat tissues. The maximum identity was 100% for both tissue samples. To the authors' knowledge, the present report is the first to describe disseminated cutaneous mast cell tumors with epitheliotropism and systemic mastocytosis in a domestic cat.