Differential alpha-smooth muscle actin expression in a gastric epithelioid leiomyosarcoma in a 14 year old girl

Leiomyosarcoma in childhood is very rare. This report describes the immunohistochemical study of a gastric epithelioid leiomyosarcoma in a 14 year old girl. Microscopically, the tumor showed two distinct histological patterns within the same tumor: small epithelioid cells forming a lobular pattern and spindle-shaped cells forming interlacing fascicles, but no distinct border divided the two types of cells. Immunohistochemically, vimentin was positive in all tumor cells; a-smooth muscle actin, however, was negative in small epithelioid cells and positive in spindle-shaped cells. The data revealed that the tumor had components showing two stages of morphological and biochemical differentiation. This case indicates that leiomyosarcomas might lose smooth muscle actin during malignant transformation; or, alternatively, they might arise from a primitive type of smooth muscle cell and some of them could spontaneously differentiate into mature smooth muscle cells, expressing this actin.