With improved survival in patients with cancer, the risk of developing multiple primary malignancies (MPMs) has increased. We aimed to characterize MPMs involving lung cancer and compare these characteristics between patients with single lung cancer and those with lung cancer and subsequent primary cancer (known as lung cancer first [LCF]). Methods: This retrospective study was conducted based on Taiwan Cancer Database from Taiwan’s National Health Insurance Registry Database. Patients with lung cancer (n = 72,219) from 1 January 2011 to 31 December 2015, were included in this study, and their medical records were traced back to 1 January 2002, and followed until 31 December 2019. Results: MPMs occurred in 10,577 (14.65%) patients with lung cancer, and LCF and other cancer first (OCF) accounted for 35.55% and 64.45% of these patients, with a mean age at lung cancer diagnosis of 65.18 and 68.92 years, respectively. The median interval between primary malignancies in the OCF group was significantly longer than that in the LCF group (3.26 vs. 0.11 years, p < 0.001). Patients in the single lung cancer group were significantly older than those in the LCF group (67.12 vs. 65.18 years, p < 0.001). The mean survival time of patients with LCF was longer than that of patients with single lung cancer. Following initial lung cancer, the three most common second primary malignancies were lung, colon, and breast cancers. For patients with advanced lung cancer, survival in patients with mutant epidermal growth factor receptor (EGFR) was longer than that in patients with undetected EGFR. In stage 3 and 4 patients with EGFR mutations, the LCF group showed better survival than the single lung cancer group. Conversely, in stage 1 patients with mutant EGFR, the LCF group exhibited worse survival than the single lung cancer group. Conclusions: Survival in patients with MPMs depends on baseline characteristics and treatments. Our findings may contribute to the development of precision medicine for improving personalized treatment and survival as well as the reduction of medical costs.
Keywords: National Health Insurance Registry Database (NHIRD); epidermal growth factor receptor (EGFR); lung cancer; multiple primary malignancies (MPMs); survival.