Breast Density Change Predicts Breast Cancer Risk Reduction In Response To Tamoxifen
Posted May 18 2011 10:08am
Many breast cancer research studies have shown that the anti-estrogen drug tamoxifen reduces breast cancer risk, which is why tamoxifen is one of only two approved breast cancer prevention drugs on the market. Tamoxifen has also been shown to reduce breast density as assessed by mammograms (i.e. mammographic breast density). Combined, this suggests that tamoxifen, at least in part, reduces breast cancer risk by reducing breast density. However, it is uncertain whether this is true in all women or whether some women benefit more than others from taking tamoxifen to prevent breast cancer.
A new breast cancer study recruited women who had taken part in the International Breast Cancer Intervention Study in order to assess the impact of tamoxifen use on mammogram breast density measures and subsequent breast cancer risk. For this study, breast cancer researchers analyzed data from 123 breast cancer patients and 942 healthy women without breast cancer. The results of this analysis showed that
46% of the women taking tamoxifen had a 10% or greater reduction in breast density as measured at their 12-18-month mammogram.
Compared to women in the control group, women taking tamoxifen who showed a 10% or greater reduction in breast density had a 63% reduced risk of developing breast cancer.
Women taking tamoxifen who had less than a 10% reduction in breast density did not see a reduction in breast cancer risk.
These results have some rather intriguing implications. The approval of tamoxifen for breast cancer prevention was based on studies showing that taking tamoxifen for 5 years reduced the incidence of ER[+] invasive breast cancers, ductal carcinoma in situ, and lobular carcinoma in situ in women at high risk for breast cancer. Therefore, tamoxifen is generally prescribed for at least 5 years when given to prevent breast cancer. While tamoxifen has been approved for the prevention of ER[+] breast cancer, this study suggests that the benefit derived from taking tamoxifen to prevent breast cancer may depend partly on tamoxifen's ability to reduce mammographic breast density. According to this new study, women who did not experience a reduction in breast density of at least 10% after taking tamoxifen for 12 - 18 months also did not see a reduction in breast cancer risk. This makes one ask whether these women should continue taking tamoxifen for breast cancer prevention. This is an important question that probably can't be answered without further research. It would be interesting to follow up this study with a larger study of longer duration. If similar results were observed in such a longer study, then using mammograms to measure the effect of tamoxifen on breast density after 12 - 18 months might suggest that women not seeing a reduction in breast density at this time might want to consider stopping tamoxifen use for breast cancer prevention. A longer study is needed to confirm these results because it is possible that tamoxifen might be working through multiple pathways besides reducing mammographic breast density and these other pathways might not come into play until after taking tamoxifen for a couple of years.