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

The 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.

We 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.

The 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).

Women 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.