Risk of second primary cancer among women with breast cancer: A population-based study in Granada (Spain)

•We examined risk of second primary cancers in women diagnosed with a first primary breast cancer in Granada (Spain).•This is the first Spanish population-based study on this issue, comprising a total of 5897 breast cancer cases.•Women diagnosed with breast cancer have higher second cancer incidence, although risk differs by age and second cancer site.

ObjectiveThe higher risk of developing new cancers in breast cancer survivors is a public health concern. Our aim was to examine risk of second primary cancers among women diagnosed with breast cancer.MethodsWe studied two cohorts of female cancer patients identified in a population-based cancer registry in Granada (Spain): women first diagnosed with a primary breast cancer (n = 5897) and those with a primary cancer in another site (n = 22,814), followed during 1985-2007 for second cancers and breast cancer occurrence, respectively. We used Standardized Incidence Ratios (SIRs) to estimate second cancer risk by age (< 50 y, ≥ 50 y), time since diagnosis (≤ 5 y, > 5 y) and calendar periods (≤ 1995, > 1996). SIR for breast cancer was calculated in the second cohort.ResultsThe risk of developing second cancers (n = 314) was 39% higher (95% CI = 1.23-1.54) among breast cancer patients, and particularly high among women under 50 (SIR = 1.96, 95% CI = 1.48-2.44). Excess risk for endometrial cancer (SIR = 3.04, 95% CI = 2.14-3.94) was statistically significant and remained so in women over 50. Younger women were at higher risk of second ovarian cancer (SIR = 4.90, 95% CI = 1.27-8.53). Increased SIRs were observed during the first five years after breast cancer diagnosis, whereas SIRs decreased thereafter. Breast cancer incidence (n = 171) was not higher among women previously diagnosed with other cancer types (SIR = 0.86, 95% CI = 0.74-1.00).ConclusionWomen diagnosed with breast cancer have a higher incidence of second primary cancers, particularly of endometrial cancer in women over 50 at diagnosis, and ovarian cancer in younger women. These findings may be explained by treatment-related effects or shared risk factors.