Myoepithelial carcinoma of soft tissue in children: an aggressive neoplasm analyzed in a series of 29 cases.

Primary myoepithelial tumors of soft tissue are uncommon, and criteria for malignancy among these neoplasms have only recently been established. Of 51 myoepithelial carcinomas of soft tissue in the literature, 11 occurred in children, 7 of which were included in a previous series of myoepithelial tumors from our group. We have collected an additional 22 cases of myoepithelial carcinoma of soft tissue in the pediatric population, and we describe the detailed clinicopathologic features of all 29 cases herein. There were 15 girls and 14 boys; age at diagnosis ranged from newborn to 17 years (median, 9 y). Sites included extremities (14 cases), trunk (6 cases), viscera (5 cases: 3 mediastinal, 1 retroperitoneal, and 1 intracardiac), and head/neck (4 cases). Histologically, the tumors were heterogeneous, with epithelioid, clear, spindle and/or plasmacytoid cells forming nests, cords or solid sheets in a myxoid or hyalinized stroma. Epithelioid cells predominated in the majority of cases (27 of 29; 93%) and in 10 cases (34%), tumor cells focally had scant cytoplasm with round cell morphology. The mitotic rate ranged from <1 to 68 per 10 high power fields (median, 8), and tumor necrosis was present in 14 cases. At least 1 broad-spectrum cytokeratin was positive in all tumors [CAM5.2 in 17 of 18 (94%), AE1/AE3 in 15 of 20 (75%), and PAN-K in 14 of 21 (67%)], and EMA was positive in 19 of 29 cases (66%). Either S100 or GFAP was positive in all but 4 cases [S100 in 21 of 29 (72%) and GFAP in 15 of 28 (54%)]. Clinical follow-up in 23 cases revealed that 9 patients had local recurrences (53% of the 17 patients who underwent complete excision with negative margins); 12 (52%) developed metastases; and 10 (43%) have died of disease so far, at a median interval of 9 months after diagnosis. Despite the relative rarity of carcinomas in the pediatric population, myoepithelial carcinoma seems to be disproportionately common among children and often has an aggressive clinical course.