Eleven cases of alimentary
lymphoma affecting the ileum were observed among 26 cases of swine
lymphoma detected by meat inspection in Kochi, Japan. The ileal
lymphomas were located in the Peyer's patches, along with early involvement of regional lymph nodes, and showed a characteristic pattern of follicular invasion leading to diffuse growth. Following the National Cancer Institute Working Formulation, 10
neoplasms were classified as diffuse, large, noncleaved cell
lymphomas and one
neoplasm was a diffuse, mixed, small to large cell
lymphoma. Both types of
lymphoma featured numerous intermingled "starry sky" histiocytes. The
lymphoma cells tended to infiltrate into the muscular layer of the ileum in an "Indian file" pattern. Two cases also showed transserosal
metastasis into the abdomen and leukemic change. The
lymphoma cells showed membrane positivity for
alkaline phosphatase and diffuse cytoplasmic staining for
acid phosphatase and
non-specific esterase. Monoclonal intracytoplasmic
immunoglobulins were demonstrated in nine
neoplasms (
IgM-lambda in seven,
IgG-lambda in one, and
IgG-kappa in one). In the areas of follicular invasion, an attenuated network of follicular dendritic cells was visualized via an antiserum against the beta subunit of
S-100 protein. Ultrastructurally, strands of dilatated rough endoplasmic reticulum and scattered or clustered dense bodies were noted. When compared with feline and human alimentary
lymphoma, including
Burkitt's lymphoma, the present
neoplasms possessed distinctive features, such as originating in Peyer's patches, transserosal
metastasis, and predominantly large B cell type with
IgM-lambda type
immunoglobulin expression, although some features were similar.