Heterotopic bone formation in rectal carcinoma. Case report and literature review.

A case of heterotopic bone formation in a primary rectal adenocarcinoma was recently observed in a 54-year-old woman. This unusual finding was present both in the diagnostic biopsy and in the subsequently resected bowel. Pertinent gross and microscopic features are presented. This report represents the twelfth case in the literature of heterotopic bone formation in a primary rectal adenocarcinoma and the first such finding in a colonic biopsy from one of these malignancies. The average age of these patients was 56 years (range 32-72) and the male-to-female ratio was 5:7. The rectum is the most common site of ossification in the gastrointestinal tract. The exact mechanism of heterotopic ossification is unknown, but it is probably the result of metaplasia of fibroblasts. Adenocarcinoma has been associated with 12 of the 16 reported cases of rectal glandular tumors with heterotopic bone.