Histologic conversion of an unfavorable primary brain lymphoma to a favorable type.

Histologic conversion of a less aggressive non-Hodgkin's lymphoma to a more aggressive type has been established in several studies. Neither this trend nor vice versa has been reported in primary brain lymphoma, because of the poor median survival in the clinical setting which precludes further invasive procedures. The authors report a case of transformation of a primary brain lymphoma, histiocytic type, to poorly differentiated lymphocytic lymphoma 2 1/2 years after treatment with radiation and intrathecal methotrexate.