Isolated bone metastases in colorectal carcinoma with synchronous invasive melanoma: a rare case report and literature review

Introduction and importance: Bone metastases as the sole manifestation of colorectal carcinoma (CRC) are extremely rare, and their coexistence with a second malignancy, such as melanoma, adds complexity to diagnosis and management. Method: A comprehensive evaluation was conducted, including PET imaging, immunohistochemistry, and genetic testing, to determine the origin of bone lesions and identify concurrent malignancies. Case Presentation: A 62-year-old male with stage III CRC developed isolated bone metastases and was simultaneously diagnosed with invasive melanoma. PET imaging and bone biopsy confirmed CRC as the source of metastases. Genetic testing identified a BRAF V600E mutation in CRC, but advanced targeted therapies were unavailable locally. Clinical Discussion: This case highlights the rarity of isolated bone metastases in CRC, the utility of PET imaging, and the implications of BRAF mutations in dual malignancies. The synchronous diagnosis of melanoma emphasized the need for integrated diagnostic approaches. Conclusion: Unusual metastasis patterns require heightened clinical vigilance and multidisciplinary care. Genetic insights can aid in understanding tumor behavior and optimizing management.