Ultrastructure of abnormal collagen in human tumors

Abnormal collagen fibrils were identified by transmission electron microscopy in 22 human tumors of differing histogenesis. They were found in a review of 1400 electron microscopy cases. Abnormal collagen fibrils, described by others as amianthoid fibers, composite collagen, collagen flowers and intrafibrillar collagen dysplasia, have been found only rarely in human tumors but commonly in certain connective tissue diseases such as pseudoxanthoma elasticum, Ehlers-Danlos syndromes, Marfan's syndrome, osteoarthritic cartilage, and emphysematous lung among others. Abnormalities in the cases described here included thickened fibrils, fibrillar degeneration of fibrils and irregular external contours. Proposed mechanisms for their formation have included degeneration possibly due to hypoxia or collagenase activity, abnormal collagen biosynthesis, and abnormal tissue levels of glycosaminoglycans. The finding of abnormal collagen fibrils in these 22 human tumors shows that their occurrence is more common than is indicated by previous published reports. Most of the tumors containing abnormal collagen fibrils were mesenchymal or soft tissue tumors. Four neuroendocrine neoplasms had abnormal collagen fibrils.