Extraskeletal osteosarcoma: a very rare case report of primary tumor of the colon-rectum and review of the literature.

Extraskeletal osteosarcoma (ESOS) is a malignant mesenchymal tumor in which neoplastic cells produce bone osteoid in variable amounts. An 81-year-old woman presented with severe abdominal pain, tenesmus, constipation and rectal bleeding. The digital rectal exploration showed a large lesion of hard consistency, occupying the lumen, with the presence of splinters that "pierced" the endoscopist's glove. Endoscopic examination and CTscan revealed an ulcerative exophytic neoplasia of the lower rectum in which multiple calcified areas were found. The lesion showed no bone involvement. An abdominal perineal resection sec Miles was performed. The histological examination revealed a highly cellular mesenchymal lesion, with spindle and epithelioid cells with moderate nuclear pleomorphism. The calcified component consisted of widespread osteoid deposition. The immunohistochemical investigations of neoplastic cells showed strong positivity for vimentin and osteonectin. The definitive histological diagnosis of primary extraskeletal osteosarcoma arising from the colon-rectum was made. To our knowledge, only one previous case of colonic osteosarcoma was published in the literature in 2001, reported by Shimazu and other authors. The extreme rarity of the tumor at this location, also confirmed by morphological and immunohistochemical data, prompted us to present this case report and to review the literature.