P1.06-005 An International Cohort of Patients with Small Cell Lung Cancer after a Non-Small Cell Lung Carcinoma Oncogene or Non-Oncogene Addicted

Abstract

Phenotypic transformation from Non-small cell lung cancer (NSCLC) to small cell lung cancer (SCLC) is a resistance mechanism in tyrosine kinase inhibitors (TKIs) treated EGFR mutant tumors. SCLC is also however less frequently diagnosed in patients without EGFR mutations treated with chemotherapy. These transformations are rare and little is known about the clinical and therapeutic characteristics of these patients. In this study we describe and compare the characteristics of SCLC arising from mutant or non-mutant NSCLC. We performed a multicentric retrospective collection (27 centers in France and Italy) of cases. Between 2005 and 2015, patients with stage III or IV NSCLC with a secondary transformation to SCLC with histological proof were included. Forty seven cases of SCLC transformation were collected, 34 in EGFR mutant and 13 in non. Most of the patients (n=37, 82%) were stage IV, (n=27, 57%) female and (n=26, 76%) had an exon 19 mutation. The last treatment before transformation was a TKI in 23 (68%) cases in the mutant group and in 3 (23%) patients (erlotinib) in the non-mutant. Median time to SCLC transformation was 17 [IQR, 11-29] months in the mutant group and 26 [IQR 23-36] months in the other (p=0.03). Molecular analyses were not performed in the non-mutant group, 25 (74%) had molecular analyses in the EGFR mutant. A driver mutation was identified in 22/25 (88%) patients: in most of the cases the same as the initial, 1 case of ALK fusion and 1 of PI3K mutation. Thirty patients (88%) received at least one line of treatment after transformation in the mutant group, in all cases a platinum-etoposide (P-E) chemotherapy. Median survival from initial diagnosis in the EGFR mutant group was significantly worse 28 [17-41] months vs 49 [36-118] months in the non EGFR mutant group (p=0.01). After transformation, the same tendency was observed with a median survival of 8 [3-12] months for the EGFR mutated patients vs 13 [6-15] months for the non EGFR mutated patients (p=0.06). SCLC that occurs in EGFR mutant treated by TKIs is more aggressive than classic SCLC, and differs on epidemiological characteristics. These transformed SCLC are not fully explained and we need to define the molecular characteristics of this cohort, before and after transformation and if funded the whole genome sequencing of the tumors to understand this TKIs mechanism of resistant.