Equine Malignant Lymphomas: Morphologic and Immunohistochemical Classification

Abstract

Gross lesions, microscopic appearance, and immunophenotyping are reported in a retrospective study of 31 cases of equine malignant lymphoma. Immunohistochemical studies were performed on archived formalin-fixed, paraffin-embedded tissues. Monoclonal antibodies to surface glycoprotein BLA.36 and intracytoplasmic domains of mb-1 and B29 were used to document the presence of B lymphocytes in the equine tumors. Polyclonal antibody to CD3 and monoclonal antibodies to T-lymphocyte markers CD3 and CD5 revealed the presence of variable numbers of T cells within the equine lymphomas. The neoplastic component of the equine lymphomas was determined through morphologic evaluation, immunophenotyping, and the use of proliferation markers Ki-67 and proliferating cell nuclear antigen. Equine malignant lymphomas were composed of a heterogeneous cell population. Most tumors contained B and T lymphocytes. Twenty-four horses had diffuse lymphomas derived from B lymphocytes. Thirteen of these lymphomas contained primarily neoplastic B lymphocytes. Eleven additional cases of diffuse large B-cell lymphoma contained from 40% to 80% nonneoplastic T lymphocytes and were classified as T-cell-rich, large B-cell lymphomas. This is the first description of T-cell-rich, B-cell lymphoma in the horse. Six tumors with a diffuse architecture were derived from T lymphocytes. Four T-cell tumors were large-cell tumors, 1 was a small-cell tumor, and in 1 tumor the size of the cells could not be determined accurately because of autolytic change in the tissues. One diffuse large-cell lymphoma did not react with either B- or T-cell markers.

Immunophenotypic Classification of Leukemia in 3 Horses

“…In equine lymphoma, an extensive immunohistochemical study has been reported, 31 utilizing antibodies and techniques suitable for examination of formalin-fixed, paraffinembedded tissues. 32 In the present study, immunohistochemical analysis performed on lymphoid tissues from horses 1 and 2 supported the results of the flow cytometric analysis of the leukemic cells.…”

Cutaneous lymphohistiocytic and multifocal lymphoma in an adult mare

“…Cutaneous lymphoma in the horse often exhibits a T-cell rich B-cell or TCRBCL immunophenotype (Kelley and Mahaffey 1998, Seahan et al 1980, Dettileux et al 1989) that is considered to represent a relatively non-aggressive subtype of the disease (de Brujin et al 2007). However, many classi fication and prognostication issues that are mainly based on histopathology and immunohistochemistry remain unresolved or are still controversial awaiting their clarification (Scott and Miller 2003).…”

Spontaneous T-cell-rich B-cell Lymphoma in a Cynomolgus Monkey(Macaca fascicularis).

“…However, in the present case some of the small-sized cells were positive for B-cell markers (CD20, CD79α) or histiocytic markers (HAM56, MAC387). Such a variety of reactive cells has not been confirmed in TCRBCLs reported in humans and other mammalian species [2,3,6,17,20,21,23,26]. The difference between human and cynomolgus monkey may be due to different cytokine profiles produced by neoplastic B-cells.…”

“…In humans, TCRBCL is characterized by an admixture of large-sized neoplastic B-cells and small-sized reactive T-cells and the latter comprises more than 50% of the whole cellular population [19]. This type of lymphoma has been reported not only in humans [3,[19][20][21], but also in other mammalian species including dog [2], cat [6,23], pig [26], and horse [17]. Histological features of TCRBCL in these animals are considered to be very similar to those of human TCRBCL.…”