Clinical-pathological challenges in the classification of pulmonary neuroendocrine neoplasms and targets on the horizon for future clinical practice.

Abstract

Diagnosing a pulmonary neuroendocrine neoplasm (NEN) may be difficult, challenging clinical decision making. In this review key clinical and pathological issues and informative molecular markers are being discussed: 1) What is the preferred outcome parameter for curatively resected low grade NENs (carcinoid) e.g., overall survival or recurrence free interval? 2) Does the World Health Organization (WHO) classification combined with a Ki-67 proliferation index and molecular markers such as OTP and CD44 offer improved prognostication in low grade NENs? 3) What is the value of a typical/atypical carcinoid diagnosis on a biopsy specimen in local and metastatic disease? Diagnosis is difficult in biopsy specimens and recent observations of an increased mitotic rate in metastatic carcinoid from typical to atypical and high-grade NEN can further complicate diagnosis. 4) What is the (ir)relevance of morphologically separating large cell neuroendocrine carcinoma (LCNEC) small cell carcinoma (SCLC) and the value of molecular markers (RB1/Rb gene/protein or transcription factors NEUROD1, ASCL1, POU2F3, or YAP1 (NAPY)) to predict systemic treatment outcome? 5) Are additional diagnostic criteria required to accurately separate LCNEC from non-small cell carcinoma (NSCLC) in biopsy specimens? Neuroendocrine morphology can be absent due to limited sample size leading to missed LCNEC diagnoses. Evaluation of genomic studies on LCNEC and marker studies have identified that a combination of Napsin-A and neuroendocrine markers could be helpful. Hence, to improve clinical practice we should consider to adjust our NEN classification incorporating prognostic and predictive markers applicable on biopsy specimens to inform a treatment outcome-driven classification.