Mantle cell lymphoma (MCL) is a low grade B-cell lymphoma; patients with this lymphoma have widespread nodal disease at the time of diagnosis, although local extranodal disease has also been reported in some cases. It is uncertain whether these two disease are identical. To determine the relationship between MCL and extrnodal lymphoma with a morphology similar to that of MCL, we compared clinical and immunohistological findings of 17 patients with MCL to those of 54 patients with other low grade B-cell lymphoma including 15 patients with extranodal lymphoma. The overexpression of PRAD1 gene and the expression of immunoglobulin shared idiotypes were also studied in these lymphomas. The patients with MCL had advanced disease with generalized lymphadenopathy on admission, a CD5+CD10-IgD+ phenotype, and PRAD1 gene overexpression. In contrast, the patients with extranodal lymphoma had localized disease on admission, a CD5-CD10-IgD- phenotype, and lack of PRAD1 expression. The patients with chronic lymphocytic leukemia (CLL) and follicular lymphoma (FL) also showed findings indicating a distinctive disease entity. The expression of shared idiotypes, which may be a serologic marker for little or no somatic mutation, were detected in only 4 of 27 FL patients, 10 of 13 MCL, 4 of 6 CLL, and 9 of 14 extranodal lymphomas. These finding suggest that 1) MCL is nodal disease and differs from extranodal lymphoma, 2) there are four distinctive disease entities within low grade B-cell lymphoma: MCL, CLL, FL, and extranodal lymphoma, and 3) MCL, CLL, and extranodal lymphoma are derived from pre-germinal center cell or cell non-entering germinal center, although FL is derived from germinal center cell.
