Metastatic squamous cell carcinoma with unknown primary site: a case report and brief literature review

YING YANGWei SunJun JiaJing YuZhiwei SunFeng DuYouwu ShiJing SunSonglin GaoYanjie XiaoXiaodong Zhang^*

• Beijing Cancer Hospital, Peking University, Beijing, China

Carcinoma of unknown primary (CUP) is a rare malignancy characterized by metastatic disease without an identifiable primary tumor, even after extensive diagnostic evaluations. This case report described a 70-year-old female patient with squamous cell CUP (SCCUP), who initially presented with elevated Carbohydrate Antigen 19-9 and a diaphragmatic mass. Despite comprehensive workup, including 18F-fluorodeoxyglucose Positron Emission Tomography-Computed Tomography and a 90-gene expression assay, the primary site remained elusive. The patient underwent surgical resection followed by two cycles of systematic therapy, and had achieved the disease-free survival of 14 months. This case underscores the limitations of current diagnostic tools and the potential role of multimodal therapy in CUP management. The discordance between molecular testing and clinical 2 findings further emphasizes the perplexing nature of CUP. The report also reviews literature on diagnosis and therapeutic options. Due to the absence of standardized regimens, future international collaboration and comprehensive genomic profiling are warranted to advance understanding of this heterogeneous disease.