Right Upper Lobe Large Cell Neuroendocrine Carcinoma with Atypical Carcinoid Features: Case Report.

Introduction: Large cell neuroendocrine carcinoma (LCNEC) and atypical carcinoid (AC) tumor are two distinct types of pulmonary neuroendocrine tumors (NETs) that are considered genetically unrelated. AC is categorized as a well-differentiated NET, while LCNEC is considered a poorly differentiated NET with a significantly poorer prognosis. Case Presentation: In this case report, we present an 83-year-old male who presented with 2-day history of hemoptysis and subsequently diagnosed with a right upper lobe carcinoid tumor on pre-excision biopsy. After evaluation of the entire excised specimen, the tumor was subsequently reclassified as LCNEC. This case is rare as the tumor displayed pathologic features of AC (areas with low mitotic activity and punctate necrosis) alternating with areas of LCNEC (high mitotic activity with sheets of necrosis). Subsequent molecular studies were more characteristic of AC, with no mutations detected in Rb1 or p53. The patient underwent surgical resection (right upper lobectomy with bronchoplasty and mediastinal lymph node dissection) to remove the tumor. Conclusion: This report outlines the clinical presentation and the underlying pathology of this rare case, which underscores the complex molecular landscape of neuroendocrine neoplasms and the need for nuanced molecular analyses in refining diagnostic approaches.