A low grade osteosarcoma of the colon

Area of Science:

• Oncology
• Surgical Pathology

Background:

• Extraskeletal osteosarcomas are exceptionally rare soft-tissue neoplasms.
• Only three prior cases of extraskeletal osteosarcoma originating in the colon have been documented.
• This report details the first case of a well-differentiated variant in this location.

Observation:

• A 58-year-old female presented with a 3-month history of lower right abdominal pain and swelling.
• Imaging revealed a large, partially calcified mass connected to the ascending colon.
• Standard laboratory tests, tumor markers, and colonoscopy were unremarkable.

Findings:

• Surgical resection confirmed a 13 cm soft-tissue tumor with a vascular pedicle attached to the colon.
• Histopathology diagnosed a low-grade osteosarcoma characterized by spindle cells and focal osteoid production.
• Immunohistochemistry showed positivity for smooth muscle actin, caldesmon, and desmin, with negativity for other markers.

Implications:

• This case expands the known spectrum of extraskeletal osteosarcomas.
• Successful surgical management of this rare colonic tumor was achieved.
• Adjuvant chemotherapy was not indicated, and the patient showed no recurrence at 6-month follow-up.