In women who are at least 50 years of age, there is no increase in late-stage breast cancer when screening mammography is performed every two years rather than annually, according to a new study. However, in younger women, biennial screening is associated with an increased risk of late-stage disease.

“These findings may be useful for policy decisions about appropriate screening intervals and for use in statistical models that estimate the costs and benefits of mammography by age and screening interval,” lead study author Dr. Emily White, from the Fred Hutchinson Cancer Research Center in Seattle, and colleagues note.

The findings, which appear in the Journal of the National Cancer Institute, are based on a study of women who were diagnosed with breast cancer after mammography screening intervals of one or two years. The former group included 5400 subjects and the latter included 2440. Late-stage breast cancer is associated with shorter survival times compared with breast cancer diagnosed at an early stage.

Among women in their 40s, the rates of late-stage breast cancer for annual- and biennial-screened subjects were 21 percent and 28 percent, respectively. This amounts to a 35 percent increased risk for biennial screening.

As noted, the screening interval had no effect on the occurrence of late-stage disease in older women, the investigators point out.

The authors also found no evidence that one type of interval was better than the other based on whether the breasts were dense or fatty. “To our knowledge, we are the first to report on this issue,” they write.

“Our findings are generally consistent with those of previous studies,” White’s team notes.

SOURCE: Journal of the National Cancer Institute, December 15, 2004.