Lung cancer is a common type of carcinoma and is the leading cause of cancer-related deaths worldwide. The two broad histological subtypes of lung cancer are non-small-cell lung cancer (NSCLC), which accounts for 85% of cases and includes adenocarcinoma and squamous cell carcinoma, and small-cell lung cancer (SCLC), which accounts for 15% of cases. Substantial improvements in treatment have led to remarkable progress and changed outcomes for many patients in the past two decades. However, with prolonged survival time and awareness of repeat biopsy, more and more patients with lung cancer have been found to undergo a histological transformation during treatment, with lung adenocarcinoma (LAdC) to SCLC transformation being the most frequent. In this article, we summarized findings on the mechanism, clinical characteristics, therapeutic strategies, and predictors of the transformation of LAdC to SCLC. A non-systematic narrative review was performed using the Pubmed/MEDLINE (US National Library of Medicine National Institutes of Health) database with the following keywords: "transformation from NSCLC to SCLC," "transformation from lung adenocarcinoma to small-cell lung cancer," "NSCLC transformation in SCLC," and "NSCLC and transformation and SCLC." Articles published until June 2022 were analyzed. Search results were limited to human studies without restriction for language.
Keywords: Lung adenocarcinoma; small-cell lung cancer; transformation.