Cutaneous epitheliotropic lymphoma with dual CD3 and c-kit expression in a dog

Carboxypeptidase A3 expression in canine mast cell tumors and tissue-resident mast cells

Mast cell tumors (MCTs) are one of the most common cutaneous malignancies in dogs. Previous studies have reported expression of mast cell–specific proteases chymase and tryptase in canine cutaneous MCTs and in connective tissue and mucosal mast cells. In humans and rodents, mast cells express an additional specific protease, carboxypeptidase A3 (CPA3). In this article, we describe CPA3 immunoreactivity in connective tissue, visceral, mucosal, and neoplastic mast cells in dogs. Positive immunolabeling for CPA3 was observed in nonneoplastic mast cells in 20/20 formalin-fixed paraffin-embedded normal tissues (skin, liver, spleen, intestine), and in 63/63 MCTs irrespective of their histological grade. CPA3 protein expression was comparable to that of c-kit in both the nonneoplastic and neoplastic mast cells. Three distinct labeling patterns (membranous, diffuse, and focal cytoplasmic) were observed for CPA3 in MCTs. The focal cytoplasmic labeling pattern was associated with high-grade MCTs staged with the Kiupel 2-tier grading criteria. We propose CPA3 as a novel immunohistochemical marker for canine mast cells in health and disease.

Evaluation of tyrosine-kinase receptor c-kit mutations, mRNA and protein expression in canine lymphoma: might c-kit represent a therapeutic target?

c-kit plays an important role in proliferation, survival and differentiation of hematopoietic progenitor cells. In human hematopoietic malignancies, c-kit is mostly expressed by progenitor cell neoplasms and seldom by mature cell neoplasms. Aim of this study was to evaluate c-kit expression in canine lymphoma. Twenty-five B-cell lymphomas and 21 T-cell lymphomas were enrolled in the study. c-kit mRNA and protein expression was measured in lymph node fine needle aspirates by quantitative real-time RT-PCR, flow cytometry and immunocytochemistry, while the occurrence of KIT mutations on exons 8-11 and 17 was investigated by direct cDNA sequencing. KIT mRNA was amplifiable but below the limit of quantification in 76% of B-cell lymphomas and 33% of T-cell lymphomas. Remaining samples showed a very low expression of KIT, except for some high grade (HG) T-cell lymphomas where a comparatively higher mRNA amount was observed. Transcriptional data were confirmed at the protein level. No gain-of-function mutations were observed. Among canine lymphomas, T-cell lymphoma typically shows an aggressive biological behavior, partly being attributable to the lack of efficacious treatment options, and the evidence of c-kit expression in HG T-cell lymphomas might represent the rationale for its routinely diagnostic evaluation and the use of tyrosine kinase inhibitors in future clinical trials.