Heterotopic bone formation in two cases of colon carcinoma

Heterotopic bone formation is rare in the gastrointestinal tract. We here p resent the clinical and pathologic details of a 56-year-old male patient wi th mucinous adenocarcinoma of the colon and a 70-year-old male patient with colon metastasis previously operated on for signet-ring-cell carcinoma of the stomach who was treated with radiotherapy postoperatively. Both of them showed diffuse bone metaplasia. Heterotopic bone formation is usually pres ent with mucin-producing benign or malignant tumors. The pathogenesis of os seous metaplasia is not well known; however, it is speculated that the extr avasation of mucin may have a stimulatory role.