Tehran University of Medical Sciences Acta Medica Iranica 0044-6025 64 6 2026 07 13 396 398 Shadi Siami Molecular Pathology Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. AND Clinical Research Development Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. Homa Hadidi Molecular Pathology Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. AND Clinical Research Development Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. Mazaher Ramezani Molecular Pathology Research Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran. AND Clinical Research Development Center, Imam Reza Hospital, Kermanshah University of Medical Sciences, Kermanshah, Iran 2024 12 29 2025 07 07 Prostate cancer is the second most frequent malignancy in men worldwide. Approximately 20% of patients present with metastatic disease. The most common metastatic sites of prostate cancer are bone, lung and pleura, non-regional lymph nodes, liver, adrenals, and brain. Metastasis of prostate cancer to the stomach and intestines is rare. Differentiation between primary and secondary colorectal cancers is difficult. Here we report a 70-year-old man who was referred to the hospital with abdominal pain, weakness, and melena. An abdominopelvic computed tomography scan was done for further investigation. As a result, colon wall thickness was increased and multiple metastatic bone foci were present. Microscopically, the results revealed malignant tumor of atypical cells with hyperchromatic nuclei. The pathologist reported a malignant undifferentiated tumor and suggested immunohistochemistry (IHC) for differentiation between malignant lymphoma and carcinoma. According to high serum PSA level, a PSA staining was also suggested and performed. IHC results showed positivity for CK (Cytokeratin) and PSA, but negativity for CK7, CK20, and LCA (Leukocyte Common Antigen) in favor of metastatic carcinoma to the colon of prostate origin. https://acta.tums.ac.ir/index.php/acta/article/view/11439 https://acta.tums.ac.ir/index.php/acta/article/download/11439/6068