LAUSR

Introduction: Histologic transformation from NSCLC to SCLC is a mechanism of resistance in EGFR‐mutant tumors but is also occasionally observed in nonmutated NSCLC. Methods: We performed a multicenter retrospective collection of cases presenting between 2005 and 2017. The objectives were to analyze survival data and to define epidemiologic, clinical, treatment and histomolecular characteristics at both the time of diagnosis of NSCLC and of SCLC. Results: Forty‐eight EGFR‐mutant NSCLC and 13 non–EGFR‐mutant cases were registered. Most EGFR‐mutant tumors retained the same EGFR mutation after transformation. The median time to SCLC transformation was shorter in the EGFR‐mutant group than in non‐EFGR mutants (16 months versus 26 months (p = 0.01)). Both tumors were responsive to platinum etoposide regimens (45% partial response for the EGFR‐mutant group versus 40% for non‐EFGR mutants). The median overall survival rates were 28 months in the EGFR‐mutant group versus 37 months in the non–EFGR‐mutant group, respectively. After transformation, the median overall survival was 9 months in the non–EGFR‐mutant group versus 10 months in the EGFR‐mutant group. Conclusions: Transformation into SCLC seems to occur more quickly in EGFR mutated tumors; however, once the tumor is transformed its survival and response to treatment seems comparable to that of classical SCLC.