“This is to our knowledge the first data…from a controlled randomized trial” to show this effect in premenopausal women, Dr. Lisa Ryden from Lund University Hospital and colleagues comment in the September issue of the European Journal of Cancer.
In their study, 564 premenopausal women with stage II breast cancer received either 2 years of tamoxifen or no adjuvant systemic treatment (control). Randomization was done without regard to estrogen receptor or progesterone receptor status of the primary tumor.
Contralateral cancers developed in 17 women taking tamoxifen and 35 women in the control group, according to their report. The median time to the second cancers was 4 years. The women who did not develop contralateral tumors were followed for a median of 14 years.
Tamoxifen significantly reduced the risk of contralateral breast cancer in all women regardless of age, with a hazard ratio of 0.5 (p = 0.02).
“The reduction was especially high in patients younger than 40 years of age (HR, 0.09; p = 0.02) and underscores that adjuvant treatment with tamoxifen is efficient in preventing a second breast cancer even in this age group,” Dr. Ryden told Reuters Health.
A reduced risk of contralateral breast cancer with adjuvant tamoxifen was also seen in women aged 40 to 49 years, although the risk reduction did not reach statistical significance in this subgroup.
In summary, the authors note, the untreated women, regardless of age, had a 12% risk of developing a contralateral breast cancer during a median of 14 years, and in women younger than 40 the risk rose to 20%. Adjuvant tamoxifen for 2 years reduced this risk by 50% for the overall group and by 90% in women younger than age 40.
While adjuvant tamoxifen reduced the risk of contralateral breast cancer in women with ER-positive and ER-negative primary tumors, the study was not large enough to permit robust conclusions regarding the effect of adjuvant tamoxifen on hormone receptor status, Dr. Ryden and colleagues point out.
Euro J Cancer 2009;45:2496-2502.