Real-World Mapping of Multiple Primary Carcinoma Combinations and Survival Outcomes in Shanghai, China: Retrospective Registry-Based Study.

backgroundMultiple primary carcinomas (MPC) represent a clinically significant yet underexplored phenomenon, where patients develop more than one distinct primary malignancy. While prior studies have examined MPC within specific cancer types, comprehensive real-world patterns of primary malignancies and their subsequent primary malignancies remain limited. Moreover, the survival outcomes associated with these MPC patterns, particularly in relation to demographic and clinical characteristics, are not well characterized.

objectiveThis study aimed to establish the patterns and combinations of MPC across a wide range of cancers and to assess whether the mortality status of patients with MPCs varies according to their demographic characteristics and disease status.

methodsWe conducted a retrospective analysis of 1560 patients with MPC in Shanghai, China, from 2002 to 2015. Data were extracted from the Shanghai Cancer Registry, with follow-up until December 2017. Cause of death was ascertained through linkage with the Shanghai Vital Registration System. The distribution of the frequency and proportion of primary carcinoma (PC) combinations were depicted, and a life table was used to calculate the 1- to 5-year survival rates. Cox regression analysis was performed to analyze the survival risk factors of the first and second PCs.

resultsAmong the 1560 patients (809/1560, 51.86% male and 751/1560, 48.14% female), the most frequent first PCs were colorectal, breast, and stomach cancers, while the most frequent second PCs were lung, colorectal, and stomach cancers. The most common combinations included colorectal and lung, colorectal and stomach, and colorectal and prostate. Survival rates were lowest for first PCs of skin (5 years=46.95%) and lung (5 years=41.54%) cancers, and for second PCs of pancreatic (5 year=9.13%) and liver (5 years=14.19%) cancers. A latency period of 12 months between PC diagnoses was associated with significantly higher cancer-specific mortality for both the first primary cancer (hazard ratio [HR] 3.539, 95% CI 2.822-4.438; P<.001) and the second primary cancer (HR 1.369, 95% CI 1.103-1.699; P=.004). Older age (>65 years) and advanced tumor stage (III+IV) were also significant independent risk factors for poor survival in both first PC (age: HR 2.049, 95% CI 1.689-2.485; P<.001; stage: HR 1.496, 95% CI 1.315-1.703; P<.001) and second PC (age: HR 1.575, 95% CI 1.242-1.996; P<.001; stage: HR 3.933, 95% CI 3.182-4.861; P<.001) analyses.

conclusionsThis study provides a comprehensive, real-world map of MPC patterns and highlights important findings: high-risk cancer combinations and key factors associated with poorer survival, including a short interdiagnosis interval (12 months), advanced age, and advanced tumor stage. Comprehensive prevention and control strategies for MPC should be developed, and clinicians should be aware of the risks of MPC in vulnerable populations during the early diagnosis stage.