Heterotopic Ossification in Colorectal Adenocarcinoma: Pathological Insights from a Rare Case

Purpose: Heterotopic ossification (HO) within colorectal adenocarcinoma is an exceptionally rare pathological finding. We report a case of colonic adenocarcinoma with mature heterotopic bone formation and summarize plausible pathogenetic mechanisms with emphasis on the bone morphogenetic protein (BMP) pathway and tumor–stroma interaction. Methods: Clinical data, preoperative imaging, endoscopic biopsy findings, and resection pathology were reviewed. Histological assessment focused on the interface between neoplastic glands, desmoplastic stroma, and osseous foci. Results: The colectomy specimen showed a well‑differentiated infiltrating adenocarcinoma invading into pericolic fat, associated with fibro‑inflammatory stroma and multinucleated giant cells. Multiple foci of mature lamellar bone with osteocytes were present in the tumor stroma, without malignant osteoid or sarcomatoid differentiation; lymph nodes were negative for metastasis. Conclusion: HO in colorectal adenocarcinoma likely reflects a locally orchestrated osteogenic program within a permissive stromal microenvironment, potentially driven by BMP signaling. Recognizing this phenomenon is important to avoid diagnostic pitfalls; its prognostic significance remains to be clarified.