The contribution of second primary cancers to the mortality of patients with a first primary breast cancer.

PURPOSE: Second primary cancers (SPCs) are estimated to affect nearly 5% of patients with breast cancer within 10 years of their diagnosis. This study aimed to estimate the contribution of SPCs to the mortality of patients with a breast first primary cancer (FPC). METHODS: A population-based cohort of 17,210 patients with a breast FPC diagnosed between 2000 and 2010 was followed for SPCs (31/12/2015) and vital status (30/06/2021). Patients diagnosed with an SPC (265 synchronous and 897 metachronous, ≤ 1 and > 1 year after the FPC, respectively) were matched (1:3, by five-year age group and year of breast FPC diagnosis) to those without an SPC and alive when the corresponding SPC was diagnosed. RESULTS: Significantly higher hazards of death were found among patients with an SPC [hazard ratio of 1.56, 95% confidence interval (CI) 1.29-1.89 for synchronous SPCs; and 2.85, 95%CI 2.56-3.17 for metachronous SPCs] compared to patients with a breast FPC only. Estimates were higher for synchronous lung, stomach, non-Hodgkin lymphoma and breast SPCs, and metachronous liver, stomach, ovary, lung, rectum, corpus uteri, colon, breast, and non-Hodgkin lymphoma SPCs. The 15-year cumulative mortality was 59.5% for synchronous SPCs and 68.7% for metachronous SPCs, which was higher than in patients with a breast FPC only (43.6% and 44.8%, respectively). CONCLUSIONS: In Northern Portugal, patients with an SPC following a breast FPC have a higher mortality compared with patients with a breast FPC only.

Second primary cancers among females with a first primary breast cancer: a population-based study in Northern Portugal.

PURPOSE: To estimate the incidence rate of second primary cancers (SPCs) and the cumulative incidence of metachronous [diagnosed > 2 months after a first primary cancer (FPC)] SPCs in patients with a breast FPC, and to compare the incidence of SPC [overall, synchronous (≤ 2 months of the FPC) and metachronous] with that expected in the general female population. METHODS: A cohort of patients with a breast FPC from the North Region Cancer Registry of Portugal, diagnosed in 2000-2010 (n = 15,981), was followed to 31 December 2015 for synchronous and metachronous SPCs. Cumulative incidence of metachronous SPCs considering death as a competing event, and incidence rates and standardized incidence ratios of SPCs were estimated. RESULTS: The diagnosis of an SPC occurred in 1229 (7.7%) of patients with a breast FPC. SPCs occurred mainly in the breast, followed by digestive organs, lung, thyroid, and female genital organs. Globally, patients with a breast FPC had a higher incidence for all types of cancer compared to the general female population, and in particular for cancers of the breast, stomach, colon, lung, lymphoma, uterus, and ovary. The 10-year cumulative incidence of metachronous SPCs following a breast FPC was 6.6% and the corresponding 10-year cumulative mortality was 26.2%. CONCLUSION: In Portugal, patients with a breast FPC have a higher incidence of cancer compared to the general female population, highlighting important aspects of care, surveillance, and counselling among this growing number of patients.