Pleomorphic leiomyosarcoma - Clinicopathologic and immunohistochemical study with special emphasis on its distinction from ordinary leiomyosarcoma and malignant fibrous histiocytoma

Pleomorphic leiomyosarcoma (PLMS) was recently described as a morphologic v ariant of leiomyosarcoma; however, its diagnostic criteria, as shown by mor phologic features and biologic behavior, remain controversial. We describe 28 cases of pleomorphic sarcoma with pleomorphic areas in more than two thi rds of the tumor and an ordinary leiomyosarcomatous fascicular area coverin g less than one third as PLMS. PLMS comprised 8.6% of all the leiomyosarcom as (322 cases) registered in our institute. Patients ranged in ap from 31 t o 89 years (average, 57.9 years). Seventeen patients (60.7%) were male and I I were female, Tumor location was as follows: the extremities in 17 cases , the retroperitoneum or abdominal cavity in 7 cases, the chest/abdominal w all in 3 cases, and the scalp in I case. Histologically, all cases showed a t least small foci of fascicles consisting of smooth muscle tumor cells, in addition to pleomorphic areas mimicking storiform-pleomorphic malignant fi brous histiocytoma. The border between pleomorphic and leiomyosarcomatous f ascicular areas was sharp in 3 cases, gradual in 2 cases, and blending in 2 3 cases. Sixteen cases (57.1%) showed a typical storiform pattern, 6 cases revealed extensive stromal hyalinization, 6 cases showed a chronic inflamma tory infiltrate, 2 cases had the foci of foamy xanthomatous cells, and 7 ca ses contained myxoid malignant fibrous histiocytoma-like areas covering les s than 50% of the tumor. The tumors had a tendency to be of a morphological ly higher grade (10 tumors were French Federation of Cancer Centers grade 2 , 18 were grade 3). Five of 28 cases (18%) showed rhabdoid features. Immuno histochemically, all of the 28 tumors examined showed a positive reactivity for at least one smooth muscle marker (desmin, muscle-specific actin, and a-smooth muscle actin) in the leiomyosarcomatous fascicular areas. In the p leomorphic areas the expression of smooth muscle markers (desmin 10 of 28, muscle-specific actin 13 of 28, and alpha -smooth muscle actin 14 of 28) wa s significantly reduced, compared with that in leiomyosarcomatous fascicula r area (desmin 18 of 28, muscle-specific actin 26 of 28, and alpha -smooth muscle actin 24 of 28). No significant difference was observed between the MIB-1 labeling, index in the leiomyosarcomatous fascicular areas (26. 10 on average) and that in the pleomorphic areas (26.17 on average). However, th e MIB-1 labeling index in PLMS was significantly higher than that in ordina ry leiomyosarcoma (n = 20, 12.86 on average) or storiform-pleomorphic malig nant fibrous histiocytoma (n = 16, 16.63 on average). In 23 patients follow -up data were available with a duration of 1-239 months. Eleven patients de veloped metastases, and lung, accounted for the most common site of metasta sis (9 cases). Fifteen of 23 patients (65.2%) died of disease. Our results indicate that PLMS should be differentiated from ordinary leiomyosarcoma be cause of its high proliferative activities and rather aggressive biologic b ehavior.