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.

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.