Risk for contralateral breast cancers in a population covered by mammography: effects of family history, age at diagnosis and histology.

BACKGROUND: Improved survival for breast cancer is increasing the likelihood of contralateral tumors. Mammographic screening is partially contributing to the survival advantage, while changing many aspects of breast cancer presentation, including age at diagnosis, histology and familial risk. As mammography has become widely used, it is important to quantify the risks for contralateral breast cancer in a population with a national access to mammographic screening service.
METHODS: The nation-wide Swedish Family-Cancer Database was used to calculate risks for contralateral breast cancer between years 1990 (1993) and 2002. The standardized incidence ratio (SIR) measured the risk for contralateral breast compared to first breast cancer.
RESULTS: The risks for contralateral breast cancer ranged between 1.85 and 3.79, and they tended to be higher when in situ cancer was diagnosed. Family history and early diagnosis of first cancer increased the risks for contralateral breast cancer, approximately equally for invasive and in situ cancers. The risk for contralateral in situ cancer was 9.01 following two independent invasive cancers. The risk for the same, concordant histology between the first and the contralateral cancer was higher than that for discordant histologies. The risks for concordant histologies were particularly high for mucinous (12.16), comedo (11.74) and lobular (5.06) tumors. When the first lobular cancer was diagnosed before age 45 years, the risk for contralateral lobular cancer was 32.20.
CONCLUSION: In situ breast cancer poses an approximately equally high risk as invasive cancer. Family history and earlier age of onset are associated with high risks needing clinical attention.