Unusual metastatic recurrence of pulmonary adenocarcinoma with a focal neuroendocrine component presenting with bilateral renal metastases and an accompanying pancreatic neuroendocrine tumor-like lesion: a case report.

A 72-year-old woman with a history of resected lung adenocarcinoma presented with a pancreatic mass and multiple bilateral renal masses. Endoscopic ultrasound-guided tissue acquisition of the pancreatic lesion showed neuroendocrine morphology, synaptophysin positivity, focal chromogranin A positivity, and a Ki-67 labeling index of 2%, leading to an initial diagnosis of pancreatic neuroendocrine tumor grade 1. Renal biopsy also demonstrated neuroendocrine differentiation with a Ki-67 labeling index of 17%. However, the pancreatic lesion was hypovascular and poorly defined, and the multifocal bilateral renal involvement was atypical for a low-grade pancreatic neuroendocrine tumor. Re-evaluation of the resected lung specimen revealed a focal neuroendocrine component showing large cell neuroendocrine carcinoma-like features, although the strict diagnostic criteria for such a diagnosis were not fully met. Genomic analysis identified a KRAS G12V mutation shared by the renal and lung tumors, supporting the interpretation that the renal lesions represented metastatic recurrence of the previously resected lung tumor. Direct molecular confirmation was unavailable for the pancreatic lesion because of insufficient residual endoscopic ultrasound-guided tissue acquisition material; therefore, its origin remained diagnostically uncertain. Nevertheless, based on the overall clinicopathological context, the pancreatic lesion was interpreted as an accompanying neuroendocrine tumor-like lesion most consistent with metastatic recurrence. This case highlights the importance of integrating clinical history, imaging features, disease distribution, archival pathology, and molecular findings when evaluating neuroendocrine tumor-like lesions in patients with a prior malignancy.