Uterine leiomyoma with indolent B-lymphoblastic proliferation.

Uterine leiomyoma with TdT positive B lymphocytes infiltrating is very rare and may simulate precursor B-cell lymphoblastic lymphoma (B-LBL). To the best of our knowledge, this is the first description of such a lesion in English literature. A 51-year-old Chinese woman was noted a mass in her uterus in a routine physical examination. The myomectomy specimen was identified as a well-defined 8.0x6.8 cm tumor and the cut surface was fresh and yellow-tan. A massive small lymphocytic infiltration accompanied by plasma cells and histiocytes was noted in the leiomyoma but not in the surrounding non-neoplastic myometrial fibers. These cells were small in size without significant nuclear irregularities and mitotic figures can not been seen. Immunohistochemical analysis has shown some small lymphocytes were CD20+, CD79a+, Pax5+B cells and some were CD2+, CD3+, CD5+, CD43+T cells. The small B cells coexpressed TdT and Ki67 and were in patchy dense distribution. The postoperative course was uneventful within a 30-month follow-up period without chemotherapy and radiotherapy. The true nature of these TdT(+) B cells has not been determined.