Clinicopathological Characteristics of Borderline Pulmonary Neuroendocrine Neoplasms

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Introduction: According to the WHO 2015 classification pulmonary neuroendocrine neoplasms (NENs) are subdivided in carcinoids and neuroendocrine carcinoma (small cell lung carcinoma and large cell neuroendocrine carcinoma (LCNEC)), based on the presence of necrosis and mitotic index (MI). However, in some NENs a discrepancy is observed between grade of differentiation and proliferation rate.

Aim(s): We aimed to describe cases with such a discrepancy referred to as ‘borderline NENs’, which we analyzed for pRb expression in relation to overall survival.

Materials and methods: Borderline cases were selected based on pathology reports of consecutive pulmonary NENs in our university medical center (Maastricht UMC+, 2007-2018) and confirmed by pathological review. Cases with well differentiated morphology, but a MI >10/2mm2 and/or Ki-67 proliferation index (PI) >20% were classified as borderline carcinoids and cases with poorly differentiated morphology, MI >10/2mm2 but Ki-67 PI ≤40% were classified as borderline LCNEC. Immunohistochemistry was performed to assess pRb expression.

Conference: 17th Annual ENETSConcerence (2020)

Presenting Author:

Authors: Hermans B, Derks J, Moonen L, Habraken C, von der Thusen J,

Keywords: Borderline tumor, NET grade 3, LCNEC, atypical carcinoid, WHO-classification,