"Most of the good prognostic factors that have been ascribed to HRT - such as smaller tumor size and earlier cancer stage at diagnosis - may simply be an artifact of screening," said Janet Daling, Ph.D., lead author of the paper, which appears in the current (November) issue of Cancer Epidemiology, Biomarkers and Prevention.
"In many cases probably the HRT itself is doing nothing, other than getting women to the doctor once a year for a prescription renewal - and a mammogram," said Daling, a member of Fred Hutchinson's Public Health Sciences Division. Daling and co-authors from five study sites nationwide reported that 90 percent of women who used combination estrogen/progestin HRT had undergone a screening mammogram within two years of breast-cancer diagnosis. In contrast, only 65 percent of women with breast cancer who'd never used HRT had undergone a mammogram during that time period.
The difference in tumor size between the two groups was significant. Among women who'd been screened within two years of diagnosis, 67 percent had tumors smaller than 2 centimeters (about the size of a pea), whereas only about 34 percent of women who hadn't been screened had tumors that small.
"I was floored when I saw this data," Daling said, "because tumor size is one of the most important prognostic factors in breast cancer. The difference in the size of the tumors between the two groups was staggering. If that isn't a good advertisement for mammography screening, then I don't know what is."