Ultrastructural observations on osteosarcoma tissue: a study of 10 cases.

Ultrastructural findings from the cellular, early osteoid regions of 10 osteosarcoma lesions are described. The characteristic features included irregularity in nuclear shape, margination of the chromatin, a large number of nucleoli, normal-sized nuclear pores, undifferentiated cells, poorly differentiated osteoblasts with scanty rough endoplasmic reticulum in annular or lamellar conformation, and malignant osteoblasts characterized by large accumulations of dilated rough endoplasmic reticulum (often in the form of huge anastomosing lakes) and by intracellular filaments. Several of the lesions demonstrated prominent giant cells, most of which were similar ultrastructurally to uninuclear tumor cells rather than to mitochondrialaden giant cells or osteoclasts. Variable amounts of primarily collagenous intercellular matrix were present. Cross-banded collagen fibers with diameters from 30-90 nm were seen as were thinner non-cross-banded fibrils 12-18 nm wide.