Case report of heterotopic bone formation in metastatic carcinoma of the colon.

The case of an 83-year-old woman, who was operated on for an adenocarcinoma of the sigmoid colon and died with retroperitoneal matastases, is described. The post mortem examination showed widespread heterotopic bone formation in these metastases. Gastrointestinal cancers and their metastases are liable to calcify and ossify, and they do so more frequently than other malignant epithelial tumors. A search through the literature led to the discovery of 35 other cases of this type. The highest frequency of heterotopic bone formation occurs in cancers of the distal portion of the large intestine and in pulmonary and lymph node metastases. The results of the present case support the view that bone formation derives from the metaplasia of stromal fibroblasts into osteoblasts. The knowledge that gastrointestinal cancers can calcify and ossify has a definite diagnostic relevance for the radiologist and gastroenterologist.