Long-term tamoxifen linked to ER - breast cancer

Long-term tamoxifen use may put survivors of estrogen receptor-positive (ER+) breast cancer at higher risk of estrogen receptor-negative (ER−) cancer in the other breast, according to research published online Aug. 24 in Cancer Research.

Christopher I. Li, MD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues analyzed data from 367 women with a first primary ER+ breast cancer, followed by a primary contralateral breast cancer, as well as 728 matched controls only diagnosed with a first breast cancer.

The researchers found that women using adjuvant tamoxifen for at least 5 years had a lower risk of ER+ cancer in the contralateral breast (odds ratio, 0.4), but a higher risk of ER− cancer in the contralateral breast (OR, 4.4). However, the use of tamoxifen for less than 5 years was not linked to risk of ER− cancer in the contralateral breast.

“Risk of a hormone receptor-negative contralateral breast cancer may now need to be tallied among the risks of treatment with tamoxifen, and further studies are needed to determine if other hormonal therapies and the increasingly used aromatase inhibitors in particular, also carry this risk. Development of ER− and ER−/progesterone receptor-negative disease is of particular clinical concern given the substantially poorer prognosis associated with these tumors compared with ER+ disease,” the authors write.

Li CI, Daling JR, Porter PL, et al. Adjuvant hormonal therapy for breast cancer and risk of hormone receptor-specific subtypes of contralateral breast cancer. Cancer Res. 2009;69:6865-6870.