Since the 1970s, tamoxifen (developed by AstraZeneca) has been shown to prevent breast cancer recurrence secondary prevention in women who were surgically treated for a primary tumor. The drug is an estrogen-receptor modifier, and since some breast cancers are estrogen-dependent (ER+), blocking estrogen s effect has in fact helped reduce the recurrence rate and lethality of those types of cancers.
Now, a large Australian study has shown that the drug has a similar beneficial effect on recurrence rate in the opposite (contralateral) breast after mastectomy among almost 2,500 women with one of the BRCA mutations: carriers of either BRCA-1 or BRCA-2.
While not definitive, given that the analysis was retrospective (backward-looking at data, rather than interventional and forward-looking), the results were quite impressive: among the 2,464 women with either of the BRCA mutations known to confer a significantly increased risk of breast (and ovarian) cancer 837 had taken tamoxifen after their diagnosis of breast cancer. Among those women, the rate of subsequent contralateral breast cancer (CBC) was a remarkable 35 percent of the rate among those who did not receive the therapy or about two-thirds lower.
The multi-center study was led by Kelly-Anne Phillips,MD, of the Peter MacCallum Cancer Centre in Victoria, Australia, and was published in the Journal of Clinical Oncology.
In a surprising outcome, the protection from secondary CBC was about the same in women with ER- tumors as it was with ER+ ones. Since it is thought that tamoxifen works by countering the effects of estrogen, it is unclear what the mechanism of its protection for those with negative estrogen receptor status is.
ACSH s Dr. Gilbert Ross had this perspective: This could be a major advance in the approach to the treatment of breast cancer in BRCA carriers, if it can be validated in more studies. However, tamoxifen is not risk-free: the most worrisome adverse effect is venous inflammation, thrombophlebitis. And while a 65 percent protective factor is impressive, many women with the very high risk of breast cancer associated with the BRCA mutation may opt for the 99 percent protection of bilateral mastectomy, as did Angelina Jolie a few months ago.