Investigators may have discovered a link between smoking and the risk of second primary cancers across various first primary cancer types, according to new findings presented by Sung et al at the 2025 American Association for Cancer Research (AACR) Annual Meeting (Abstract 4942/20).
Study Methods and Results
In the study, the investigators used the Cancer Prevention Study II Nutrition Cohort to identify 28,272 participants. They analyzed patients who were diagnosed with first primary invasive, nonmetastatic cancers between January 1, 1992, and June 30, 2015, and survived for 1 year or more. About 59% of the patients were male and 49% of patients were aged 70 to 79 years at their first primary cancer diagnosis. The most common first primary cancers were prostate cancer (33%), breast cancer (19%), colorectal cancer (9%), and non-Hodgkin lymphoma (8%). The patients were followed for second primary cancer diagnoses until June 30, 2017.
Smoking prevalence was highest among the patients with first primary cancers of the lung (88%), esophagus (78%), and bladder (75%); and lowest among those with endometrial (39%) and nonmucinious ovarian (39%) cancers. The investigators found that the association remained even when the first cancers were not smoking related.
During a median follow-up of 7 years, 7% (n = 1,926) of the patients developed smoking-related second primary cancers. Former and current smokers were more likely compared with never-smokers to develop smoking-related second primary cancers. The investigators detailed that the hazard ratio (HR) for current smokers varied across first primary cancer types: 5.8 for endometrial cancer, 4.9 for colorectal cancer, 4.1 for prostate cancer, 3.9 for melanoma, 3.3 for breast cancer, 3.1 for non-Hodgkin lymphoma, and 2.8 for urothelial carcinoma. Among former smokers overall, HRs declined with years since quitting from 2.6 for less than 10 years to 1.3 for 30 years or more prior to first primary cancer diagnosis.
The risk reduction was most marked for endometrial cancer survivors after 10 years or more and breast cancer survivors after 20 years or more since quitting, although a lower-level risk persisted for several other first primary cancers.
Conclusions
The findings highlighted the significance of smoking cessation initiatives in reducing the burden of second primary cancers among the population of cancer survivors.
Disclosure: For full disclosures of the study authors, visit abstractsonline.com.
