Prognostic factors, treatment decisions, and nomograms for patients with second primary lung cancer following colorectal cancer: a population-based study.

Colorectal cancer (CRC) survival rates continue to improve, but the risk of developing a second primary malignancy (SPM) has also increased. The most common type of SPM observed after CRC is lung cancer. In this study, we explored the prognostic factors and clinical management decisions of patients with second primary lung cancer after colorectal cancer (SPLC-CRC). We identified the data of 1637 patients with SPLC-CRC from the Surveillance, Epidemiology, and End Results (SEER) database between 2004 and 2015. Cox regression modeling was used to construct a nomogram for predicting the prognosis of SPLC-CRC patients. The Fine-Gray competing risk model was used to determine the association between factors and cancer-specific mortality. After this, survival analyses were performed to assess the benefit of each treatment method on overall survival (OS). According to a multivariate analysis, age, gender, surgery, and chemotherapy were independent prognostic factors for the first primary malignancy (FPM), whereas age, primary site, TNM stage, tumor size, and treatment were independent prognostic factors for the second primary malignancy (SPM). For the training cohort column chart as well as the validation cohort column chart, using the concordance index of OS, 0.7611 and 0.7605 were calculated. A Fine-Gray competing risk model and survival analysis showed that there is a significant correlation between the treatment of FPM and the improvement in SPM survival rates, FPM-diagnosed patients who undergo surgery in different pathological stages exhibit higher overall survival rates, Patients in stages II, III, and IV benefit from combined surgery and chemotherapy. SPM surgery (P < 0.001, HR = 0.230, 95%CI 0.032-0.426) was a protective factor for lung cancer-specific mortality. Patients with local, regional, and even distant metastases may benefit more from SPM surgery (P < 0.001, P < 0.001, and P < 0.001, respectively). In patients who did not undergo SPM surgery, radiotherapy (P < 0.001) and chemotherapy (P = 0.008) improved OS. Treatment strategy for the first tumor affects the prognosis of the second tumor significantly. SPLC-CRC is treated primarily with surgery, regardless of whether the patient has metastases, as surgery may improve outcomes. In the event that a patient is unable to undergo surgery, chemotherapy or radiotherapy should be considered. Treatment decisions for SPLC-CRC patients may be influenced by these findings.