Undifferentiated leiomyosarcoma showing various sarcomatous components with incidental B-cell lymphoma after tumor recurrence

We report a rare case of undifferentiated leiomyosarcoma (LMS) with incidental B-cell lymphoma in a 70-year-old woman. T2-weighted magnetic resonance images revealed a high signal intensity mass measuring 9 × 8cm in the gluteus muscle. The pathological diagnosis of repeated surgery was undifferentiated LMS that included various sarcomatous components, such as fibrosarcomatous, rhabdomyosarcomatous, and malignant fibrous histiocytomalike elements. A specimen from a supraclavicular lymph node showed the characteristics of malignant B-cell lymphoma (follicle type). Adjuvant chemotherapy or radiation therapy was not performed because of the patient's advanced age. The patient died from liver metastasis and dysfunction 5 years 8 months after the initial therapy. This is a rare case of LMS with malignant lymphoma. Considerable debate remains whether the B-cell lymphoma developed incidentally.