Giant primary cutaneous spindle cell B-cell lymphoma of follicle center cell origin.

Spindle cell B-cell lymphoma is a rare morphologic variant of B-cell lymphoma that is generally associated with follicle center cell origin. It is typically found on the skin and presents as single nodule or plaque with a diameter of several centimeters. It is also characterized by abnormal spindle cells with elongated or spindle-shaped nuclei, and usually stained positive for Bcl-6 and negative for multiple myeloma oncogene 1 (MUM-1). In this report, we describe a giant primary cutaneous spindle cell B-cell lymphoma measured 20 cm × 25 cm, substantially larger than all the previously reported cases. Histologic examination revealed that the neoplasm was mainly located in the dermis and subcutaneous fat, and had infiltrated into striated muscles of the patient's back. The neoplasm cells contained elongated or spindle-shaped nuclei. Immunohistochemistry results demonstrated that the neoplasm cells were stained positive for CD20, CD79, and Bcl-6, negative for Bcl-2 and MUM-1, and focally positive for CD5, CD10, CD31, and CD43. These results collectively indicated that the neoplasm was of follicle center cell origin. The neoplasm was excised and the patient was still alive without systemic involvement after 4 years of follow-up.