Background: Mast cell tumors (MCTs) with bone marrow (BM) involvement are poorly documented in dogs and are associated with a poor prognosis. Successful treatment strategies have not been described.Hypothesis: Clinicopathologic findings of affected dogs are not specific. Administration of lomustine or imatinib is beneficial.Animals: Fourteen dogs with MCT and BM involvement. Methods: Clinical and laboratory evaluations were performed in each dog on admission and during follow-up. All dogs received prednisone. Additionally, 8 dogs received lomustine and 3 dogs received imatinib. Imatinib was administered if tumorassociated tyrosine kinase KIT was aberrant.Results: On admission, 11 dogs had a single cutaneous nodule and 3 dogs had multiple nodules. Involvement of regional lymph nodes, liver, or spleen was observed in each dog. BM infiltration with mast cells (MCs) was observed in all dogs. On CBC, nonregenerative anemia, leukopenia, or thrombocytopenia was common. Four dogs had circulating MCs. Increased alkaline phosphatase or alanine transferase activity was observed in 12 and 10 dogs, respectively. Treatment with lomustine induced partial remission in 1 of 8 dogs. Median survival time was 43 days (range, 14-57). Dogs on imatinib experienced complete remission. Two dogs survived for 117 and 159 days, and the third was alive after 75 days. Dogs treated symptomatically did not improve and were euthanized after 1, 14, and 32 days.Conclusions and Clinical Importance: A combination of clinical and laboratory evaluation helps in identifying dogs with MCT and BM infiltration. Administration of lomustine is not helpful in affected dogs. The beneficial effect of imatinib warrants further investigation.

Telomere length maintenance is regarded as a fundamental step in tumorigenesis, as most human brain tumors, including meningiomas, stabilize the ends of their chromosomes using telomerase. This investigation represents an introduction to telomerase expression in canine and feline meningiomas. Twenty-five archived cases (14 dogs and 11 cats) were immunohistochemically tested for human-telomerase reverse transcriptase (h-TERT), scored, and quantified; furthermore, mitoses were counted on sections stained with a modified toluidine blue. The h-TERT antibody immunolabelled the nucleus and nucleolus of meningeal neoplastic cells, with an intensity ranging from mild to strong and a speckled distribution; a significantly higher expression in cats was noted, while no significant association between h-TERT immunolabelling and sex or histotype was evident in dogs or cats. The telomerase enzyme represents a fundamental parameter of potential malignant transformation, which may occur independently of the signal to proliferate, thereby supplying the cells with unlimited growth capabilities. Telomerase expression could be a prognostic indicator independent of the kinetic parameters, although this should be evaluated using a larger dataset with available clinical information.

Abstract. In this study, 30 feline intestinal T-cell lymphomas (ITCLs) from 77 cats with gastrointestinal lymphoma were evaluated. Neoplastic lesions were composed predominantly of small (n 5 21) or medium to large (n 5 9) anaplastic cells. Different patterns of tumor growth were observed. A starry-sky pattern was evident in 7 cases (23.3%), fibrosis in 18 cases (60%), and neovascularization in 19 cases (63.3%). The cell proliferation index (assessed by MIB1 [mindbomb homolog 1] immunohistochemistry) ranged from 0.21% to 66.91%. Mean MIB1 index was 3.49% within the first 33rd percentile, 18.31% within the second 33rd percentile, and 40.16% within the third 33rd percentile (P , 0.000001). Microscopic and kinetic features provided evidence that ITCL in cats exhibits a spectrum in cytological composition and growth patterns that could putatively reflect differences in biologic behavior.

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