Dedifferentiated leiomyosarcoma: clinicopathological analysis of 18 cases

Aims: To clinicopathologically characterize the dedifferentiated variant of leiomyosarcoma in a series of 18 cases. Methods and results: Dedifferentiated leiomyosarcoma was defined as showing features of low-grade leiomyosarcoma associated with a discrete undifferentiated component lacking morphological or immunophenotypic features of myogenic differentiation. Tumours developed in 11 women and seven men, with an age range of 16-84 years (median, 64 years). Sites were retroperitoneum (eight cases), limbs (four), trunk (two) uterus (two), and paratesticular and prostate (one each). In 17 cases, dedifferentiation occurred de novo in the primary tumour. Tumour size ranged from 50 to 280 mm (median: 120 mm). Histologically, most showed discrete transition from well-differentiated smooth muscle morphology to high-grade pleomorphic morphology with no smooth muscle differentiation. Unusual features in the dedifferentiated component (epithelioid and rhabdomyoblast-like morphology) were present in three cases. Heterologous osseous or chondro-osseous elements were present in two cases. Dedifferentiated areas were negative for myogenic markers in all cases. Follow-up for 13 cases (median, 36 months) showed local recurrence in 38% (5/13). So far, three patients have died of disease (median survival, 8 months), and metastasis developed in five of 13 cases. Conclusions: Dedifferentiated leiomyosarcoma has morphological parallels with other types of dedifferentiated sarcoma, and is clinically aggressive.