SATURDAY, May 5, 2007 (HealthDay News) -- The decline in U.S. breast cancer cases is caused not only by fewer women using hormone replacement therapy but also by the use of mammography screening, new research suggests.
"Two distinct patterns are observed in breast cancer trends," wrote Dr. Ahmedin Jemal, strategic director for cancer surveillance for the American Cancer Society, in a report published in the May 3 online edition of the journal Breast Cancer Research.
After colleagues presented an abstract at a breast cancer symposium that attributed the 7 percent decline in U.S. breast cancer cases in the years 2002 to 2003 to the reduced use of hormone replacement therapy, Jemal's team decided to look at an older data base.
The researchers who linked the decline to reduced hormone use looked at a large data base from 2002 and 2003 called SEER (Surveillance, Epidemiology, and End Results). In 2002, a large federally funded trial -- part of the Women's Health Initiative -- was halted when evidence emerged of an increased risk of heart disease and breast cancer due to hormone therapy.
After that, women in large numbers went off their hormone replacement regimens.
But Jemal's team looked at older SEER data bases, from 1975 to 2003. The researchers looked at breast cancer incidence rates by tumor size, tumor stage, and whether the tumor was estrogen-receptor positive or negative among women who were age 40 or older in the years studied.
They found that the decline in breast cancer cases also dropped prior to the 2002-2003 SEER data, although the decrease was less dramatic -- about 5 percent between 1999 and 2000, according to Jemal.
"The point is breast cancer started to decrease before 2002," Jemal said. And screening mammograms were the reason, he added.
The decline in breast cancer rates directly attributed to mammography, he said, has now leveled off.
"The message for women over 40 is still, they should get a mammogram every year so the tumor [if there is one] can be detected," Jemal said.
The new study is "a more nuanced analysis," said Roshan Bastani, professor and associate dean for research at the University of California, Los Angeles, and associate director for cancer prevention and control at the university's Jonsson Comprehensive Cancer Center. "It shows there were declines in breast cancer that started before the recent declines."
While from a public health perspective a plateau may have been reached when it comes to the benefits of screening mammography, Bastani added, it's still crucial for women over age 40 to keep their mammogram appointments. "About 75 percent of [U.S.] women are getting screened. That has not changed since 1999," she said.
To learn more about breast cancer, visit the American Cancer Society.