According to the study authors, who presented their findings Thursday at the annual San Antonio Breast Cancer Symposium, this was the largest single drop ever in breast cancer incidence within a single year. “Something went right,” study author Dr. Peter Ravdin, a research professor in biostatistics at M.D. Anderson Cancer Center in Houston, said in a statement.
Further analyses revealed that the decline was most evident in patients older than 50 and for estrogen receptor-positive tumors. The steepest decline (12 percent) was in women aged 50 to 69 who had estrogen receptor-positive tumors. Women in that age range with estrogen receptor-negative tumors saw a 4 percent decline in incidence.
Women with estrogen receptor-positive breast cancer showed an 8 percent decline vs. 4 percent for women estrogen receptor-negative breast cancer.
The incidence of breast cancer in the United States had been increasing for the two decades prior to July 2002, and experts had speculated that HRT may have played a role.
According to the researchers, about 30 percent of women over the age of 50 had been taking HRT in the first part of this decade and about half of those stopped using HRT in late 2002. Estrogen receptor-positive tumors will stop growing if the fuel they need is cut off, which may explain the suddenness of the decline.
Still, it’s not certain that HRT caused the decline, only that the association is a strong one and further studies need to be done, the researchers stated.