New guidelines for breast cancer drug tamoxifen increase survival
Tamoxifen is widely prescribed to reduce the risk of breast cancer in women who have estrogen receptor (ER)-positive early breast cancer. The drug blocks the effects of estrogen, which can help breast cancer cells survive and grow. Most women with estrogen-sensitive breast cancer benefit from this drug. A five year course of therapy has been commonly prescribed; however, the results of a new study suggest that the drug should be taken twice as long. The study was conducted by an international team of researchers; it was published online in The Lancet and also presented at the San Antonio Breast Cancer Symposium.
The researchers noted that treatment with tamoxifen for five years substantially reduces the breast cancer mortality rate throughout the first 15 years after diagnosis. They conducted a study to further assess the effects of the medication by extended the treatment to 10 years.
The worldwide “Adjuvant Tamoxifen: Longer Against Shorter (ATLAS) trial” comprised 12,894 women with early breast cancer who had completed five years of treatment with tamoxifen. They were randomly assigned to continue tamoxifen to 10 years or stop at five years (control group). Half the subjects were assigned to each arm of the study. The women were enrolled between 1996 and 2005; following enrollment, yearly follow-up forms recorded any recurrence, second cancer, hospital admission, or death. The investigators reported the effects on breast cancer outcomes among the 6,846 women with ER-positive disease, and side-effects among all women (with positive, negative, or unknown ER status). Long-term follow-up is ongoing.
The investigators found that among women with ER-positive disease, allocation to continue tamoxifen reduced the risk of breast cancer recurrence (617 recurrences in 3,428 women allocated to continue vs. 711 in 3418 controls), reduced breast cancer mortality (331 deaths vs. 397 deaths), and reduced overall mortality (639 deaths vs. 722 deaths). The reductions in adverse breast cancer outcomes appeared to be less extreme before than after year 10 (recurrence rate ratio (RR): 0.90 during years 5-9 and 0.75 in later years; breast cancer mortality RR: 0.97 during years 5-9 and 0.71 in later years).
The cumulative risk of recurrence during years 5-14 was 21.4% for women allocated to continue versus 25.1% for controls; breast cancer mortality during years 5-14 was 12.2% for women allocated to continue versus 15.0% for controls (absolute mortality reduction: 2.8%). Treatment allocation appeared to have no effect on breast cancer outcome among 1,248 women with ER-negative disease, and an intermediate effect among 4,800 women with unknown ER status.
Among all 12,894 women, mortality without recurrence from causes other than breast cancer was little affected (691 deaths without recurrence in 6,454 women allocated to continue versus 679 deaths in 6,440 controls; RR: 0.99). For the incidence (hospitalization or death) rates of specific diseases, RRs were as follows: pulmonary embolus 1..87 (including 0.2% mortality in both treatment groups); stroke 1.0636); ischemic heart disease 0.76); and endometrial cancer 1.74. The cumulative risk of endometrial cancer during years 5-14 was 3.1% (mortality 0.4%) for women allocated to continue versus 1.6% for controls (absolute mortality increase 0.2%).
The researchers concluded that for women with ER-positive disease, continuing tamoxifen to 10 years rather than stopping at five years produces a further reduction in recurrence and mortality, particularly after year 10. They added that their results, taken together with results from previous trials offive5 years of tamoxifen treatment versus none, suggest that 10 years of tamoxifen treatment can approximately halve breast cancer mortality during the second decade after diagnosis.
Reference: The Lancet
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