Neither Tamoxifen nor Arimidex are recommended for hormone-negative cancer. Breast cancer research, especially from the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), demonstrates that these drugs do not help hormone-receptor-negative cancer. The Arimidex Web site specifically notes that the drug is for women with estrogen-positive breast cancer.
The situation gets a little muddy in terms of weakly positive tumors, which was true in my case—I was weakly positive for progesterone. These tumors are considered a mixture of positive and negative and, therefore, might react to the anti-estrogen drug Tamoxifen or an aromatase inhibitor like Arimidex. Wendy Chen, MD, of Dana Farber Cancer Institute and Brigham and Women’s Hospital and a participant in the Nurses Health Study (NHS) research, says the NHS studies classify a tumor as hormone positive if it is even borderline positive. So those of us with mixed readings, in that case, would have been included in the data for estrogen-positive patients.
Still, she says, “The cut-off for ER positivity can vary from lab to lab and study to study.” Because of this, she says, “there is no one right answer” to the question of whether Tamoxifen or Arimidex might help women with weakly positive tumors.”
According to the CTS, even though tumors of hormone-negative cancer do not need estrogen to grow, at the stem-cell stage they may be initially formed because of out-of-kilter hormones that are linked to insulin. So, while estrogen is not the perpetrator, it may be an accessory to the crime, aiding insulin in the initial formation of the disease.
Tamoxifen, then, could be of some benefit, says Leslie Bernstein, PhD, professor and dean for faculty development at the City of Hope National Medical Center. Bernstein, who was a researcher on the CTS study, says that Tamoxifen “suppresses the insulin-like growth factor. Its effects could work with ER-negative cancer.”
Data from the Early Breast Cancer Trialists’ Collaborative Group (EBCTCG), show the overall recurrence rate after five years for women on Tamoxifen as 3.2 percent a year. For women who had not taken Tamoxifen, it was 4.5 percent a year. This is an average, of course, so half of the women in the study had higher recurrence rates, half had lower. Does this mean that women with mixed or weak readings would benefit less than average? That sort of information may be embedded in research, but I have yet to dig it out. I’ll keep trying.
Again, we get back to the fact that cancer is as unique as our DNA, so one woman’s breast cancer is not the same as another’s, and the decisions on treatment have to be made based on her specific circumstances.