Myofibroblast activity of radial scars.

Radial scars from 38 cases, comprising 12 associated with cancer and 26 with benign lesions, have been examined by electron microscopy. One-third of the lesions, regarded as being at an early stage of development, showed abundant spindle cells, which displayed the ultrastructural characteristics of myofibroblasts. These included many profiles of endoplasmic reticulum, prominent myofilaments and a close association with collagen and elastic fibres. The remaining 'mature' radial scars showed relatively few myofibroblasts, sparsely distributed in the stroma. The stromal cells associated with the 'early' lesions were seen in close proximity to degenerating parenchymal structures, which frequently showed loss of basal lamina. Obliteration of the central parenchymal component appeared to be a prominent feature of radial scar formation. The ultrastructural appearances are consistent with a progressive development of the lesion, associated with sporadic myofibroblast activity.