Malignant tumors are known to have an heterogeneous cell population. Metastases are supposed to be formed by subpopulations with high metastatic capability. These metastatic cells constitute the so called invasive phenotype. In that order of ideas, metastases could be pathologically different from their parent tumors if the invasive phenotype had distinct morphological features. The similarities or differences between primary tumors and their metastases have not been adequately studied at the ultrastructural level. In this work we report an electron microscopic study of liver leiomyosarcoma metastases which shows alterations not described in primary tumors of that kind.

Biopsies of liver metastases from a colon leiomyosarcoma were surgically obtained. Samples were processed with routine techniques for transmission electron microscopy and observed in a Hitachi H-500 electron microscope.

Some alterations usually observed in primary leiomyosarcomas were seen. They were presence of myofilaments with focal densities, nuclear changes, swollen mitochondria, and abundance of rough endoplasmic reticulum (Fig. 1).