Squamous Cell Carcinoma of Unknown Primary: Multiple Skeletal Metastases Without Detectable Visceral Lesions

The appropriate diagnosis of carcinoma of unknown primary can be challenging for physicians, especially when they cannot apply a logical and ordered diagnostic process due to the unorthodox clinical characteristics. Here, we report the case of a 75-year-old woman presenting with multiple skeletal metastases with neither detectable visceral lesions nor site-specific distribution. Histological examination of a skeletal biopsy specimen unexpectedly revealed squamous cell carcinoma (SCC). Further specialized investigations led to the diagnosis of SCC of unknown primary. This case highlights the difficulty of the clinical differential diagnostic process in the quest for the occult primary tumor site.