There is no way to prove why the risk of developing breast Ca in the US hit an upward trend in the 1980s and 1990s, seemed to level off for a while, then dropped precipitously in 2003 compared with the year before. . .
There's no way to prove why the risk of developing breast cancer in the United States hit an upward trend in the 1980s and 1990s, seemed to level off for a while, then dropped precipitously in 2003 compared with the year before, explained researcher/presenter Peter Ravdin, MD, of MD Anderson Cancer Center at the NAMS Meeting. The abrupt drop (about 50%) in hormone therapy use in the wake of the initial Women's Health Initiative (WHI) report linking combined HT to a higher breast cancer risk is one possible explanation. But changes in breast cancer rates have also been linked to changes in mammography use. But, yes, he said, epidemiologic and clinical trial evidence do show that combined estrogen/progestin use confers a particular risk.
"A crucial piece of upcoming evidence will be, what happened to the women in the (prematurely stopped) WHI combined trial after stopping combined HT in 2002," he said, adding that results are expected in 2008.
Ravdin also pointed out that the drop occurred only in women in the age 50 or older group and chiefly among those with estrogen-receptor positive breast cancers. Discussing the SEER data reported in his recent New EnglandJournal of Medicine article, Dr. Ravdin reiterated its conclusion that the 9% decrease in breast cancer "seems related to WHI, but other causes can't be excluded." Citing the California Registry study of 3 million women, which broke down breast cancer incidence by counties having high use and low use of HT, he said, "They saw the same results as we saw." Weakening the mammography argument was that there was no change in mammography use in that state during this period. He also pointed to questionnaire findings from the National Cancer Institute analysis regarding mammography use in the 50- to 64-years age group, which showed a decrease in screening mammography use during the period of the drop in breast cancer rates-but not enough of a decrease to account for the lower cancer rates.
Jemal A, Ward E, Thun MJ. Recent trends in breast cancer incidence rates by age and tumor characteristics among U.S. women. Breast Cancer Res. 2007;9:R28.
Ravdin PM, Cronin KA, Howlader N, et al. The decrease in breast cancer incidence in 2003 in the United States. N Engl J Med. 2007;356:1670-1674.
Robbins A, Clarke C. Regional changes in hormone therapy use and breast cancer incidence, California, 2001-2004. J Clin Oncol. 2007 [Epub ahead of print].