Lessons From the Friday Unknowns
Histologic sections show a large lymph node in which the architecture is almost completely replaced by lymphoma. The neoplasm surrounds a few residual reactive germinal centers. At low power magnification, pale areas can be appreciated consistent with proliferation centers. These areas are composed of small lymphocytes, prolymphocytes and paraimmunoblasts. The remainder of the neoplasm is composed mostly of small round lymphocytes. There are no areas of necrosis and the mitotic rate appears to be low.
We have reviewed immunohistochemical studies performed elsewhere. The neoplastic cells are positive for CD5, CD20 (weak), CD21, CD30 (subset, 5–10%), PAX–5, BCL–2, MUM1/IRF4 (mostly in proliferation centers), MYC (in proliferation centers), FOXP1 and LEF1, and are negative for CD3, CD10, BCL–6 and cyclin D1. The antibody specific for Ki-67 shows a proliferation rate of approximately 10–15% overall, with many areas 5–10% and a few small areas up to 20–25%.