Diagnostic Challenges and Multidisciplinary Management of Invasive Mediastinal Adenocarcinoma: A Case Report.

Adenocarcinoma rarely manifests as a bulky, invasive mediastinal tumor. Even more unusual is when such a tumor, initially diagnosed as another malignancy on biopsy, is later identified as an adenocarcinoma of unknown primary origin. A 46-year-old man with no prior history of malignancy was diagnosed with primary mediastinal seminoma and received chemotherapy before being referred to our hospital. At referral, the tumor had shrunk to half its original size, measuring 7 cm in maximum diameter. Due to its extensive invasion, we performed a combined resection, including the resection and reconstruction of the superior vena cava, achieving complete tumor removal. However, the resected specimen showed extensive necrosis, making it unidentifiable as a tumor. This prompted a reexamination of the pretreatment biopsy, which led to a revised diagnosis of "adenocarcinoma not otherwise specified with clear cell features." Immunohistochemical staining suggested a lung cancer profile, but systemic examination failed to identify the primary site, resulting in a final diagnosis of carcinoma of unknown primary. The cancer recurred 26 months after surgery, and the patient underwent repeated chemotherapy up to the fourth line. He survived for 92 months after surgery before passing away. This case highlights the diagnostic challenges posed by invasive mediastinal adenocarcinoma of unknown primary. It also demonstrates that multidisciplinary treatment - combining induction chemotherapy, curative surgery, and post-recurrence chemotherapy - can enable long-term survival, even in such complex cases.