Ectopic β-HCG Production in a Young Patient with Highly Aggressive Metastatic Lung Adenocarcinoma: A Rare Paraneoplastic Manifestation

: We report an exceptionally rare case of β-hCG–producing lung adenocarcinoma in a 23-year-old patient, likely among the youngest described to date. The patient presented with progressive respiratory symptoms and was initially managed as cancer of unknown primary following non-diagnostic biopsies. Subsequent biopsies of metastatic lesions demonstrated strong β-hCG expression, leading to an initial misdiagnosis of a germ cell tumor and initiation of BEP chemotherapy. Comprehensive molecular analysis later revealed KRAS and TP53 mutations, with a methylation profile consistent with non-small cell lung cancer. Despite multiple lines of therapy, the disease exhibited an aggressive clinical course with rapid progression. This case underscores the importance of recognizing ectopic β-hCG secretion as a rare paraneoplastic phenomenon in lung cancer, particularly in young patients, and highlights the risk of diagnostic missclassifications. Furthermore, it suggests that deeper investigation into β-hCG–mediated signaling pathways may offer potential avenues for the development of novel therapeutic strategies.