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

Abstract

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 (<50y, ≥50y), time since diagnosis (≤5y, >5y) 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.