Lung carcinoids with high proliferative activity: Further support for the identification of a new tumor category in the classification of lung neuroendocrine neoplasms

Abstract Highly proliferative lung carcinoids (HPLC) have been recently reported but information about this subset remains scarce. Objectives Clinical and pathological data of 630 patients with lung carcinoids (LC) referred to Gustave Roussy (GR) or European Institute of Oncology (IEO) were retrospectively reviewed to select HPLC and analyze their frequency, behavior and compare their outcome to conventional LC with Ki-67 ≤ 20 % and mitotic count (MC)≤10/2 mm2. Materials and methods Selection criteria were: diagnosis of LC confirmed by local pathologist, and available clinical and follow-up data. Patients with Ki-67 > 20 % and/or MC > 10/ 2 mm2 in primary or metastatic specimens were identified as HPLC. Results 30/514 patients (6%) met the selection criteria of HPLC. Based on primary tumor evaluation, 22/25 (88 %) were classified as atypical carcinoids (AC). Median MC was 4.5/2 mm2 (1–11) 6/2 mm2 (3–15) in primary and metastatic tumors, respectively. Median Ki-67 was respectively 23 % (15–65) and 25 % (8–60). Recurrence rate was 66 % (12/18) in HPLC and 9 % (33/352) in conventional LC. Median RFS was 24 (10-NR) months in HPLC, 288 (141-NR) months in LC with Ki-67 index≤5 % and NR (148-NR) months in LC with Ki-67 6−20% (p  Conclusion This study confirms the existence and rarity of HPLC. Their characteristics and clinical behavior are more similar to LC rather than neuroendocrine carcinomas (NECs), suggesting that this entity could be managed accordingly.