Women with breast cancer are more likely to have a second breast cancer than women in the general population are to have a primary cancer. However, the biological relationship between primary and second breast cancers is not clear.
A total of 30,617 patients diagnosed with bilateral breast cancers between 1990 and 2007 were identified through 17 cancer registries of the Surveillance, Epidemiology, and End Results program. Logistic regression with odds ratios (ORs) and 95% confidence intervals (CIs) was used to model strength of association in hormone receptor status, grade, and histology between 2 cancers.
There was a strong association in estrogen receptor status between 2 bilateral tumors (OR, 7.64; 95% CI, 7.00-8.35). The strength of association in estrogen receptor status depended on the time interval between the first and second tumors and age at diagnosis. The OR was 25.9 for synchronous tumors (within 1 month) and 3.69 for metachronous tumors separated by ≥10 years. The strength of association was stronger in patients whose first cancer was diagnosed before age 50 (OR, 11.7) versus after age 50 (OR, 5.71). A similar pattern was observed for progesterone receptor, grade, and histological type, but with relatively weaker association.
The strong concordance in hormone receptor status of primary and second breast cancers suggests that 2 breast cancers arise in a common milieu and that tumor subtypes are predetermined in the early stage of breast carcinogenesis.