The authors of a recent study analyzed data from the National Cancer Institute's U.S. Surveillance, Epidemiology, and End Results (SEER) databases to determine breast cancer incidence between 1976 and 2009. They looked at localized disease (cancer only in the breast), regional disease (additional cancer in contiguous and adjacent organs), and distant disease (remote metastases).

The data revealed a small but steady and statistically significant increase in the incidence rate of distant breast cancer in women ages 25 to 39 years; the rate increased from 1.53 per 100,000 women in 1976 to 2.9 per 100,000 women in 2009. This trend was evident across races and ethnicities and was independent of residence (metropolitan or rural). The greatest increases were seen in white and black women, as well as in those with estrogen receptor-positive tumor subtypes. Rates didn't increase in the older age groups or in women 25 to 39 years of age with regional or localized disease.

Although the authors admit that this increase could be due to "stage migration," in which a trend toward higher classification results from improvements in diagnostics and other factors, they state that there are likely a number of causes for the increase and that their findings need to be confirmed and clarified by additional studies.

They also state that, although the increase is small, it is of concern because it affects an age group that doesn't receive routine screenings, has the lowest rates of health insurance coverage, and has the worst prognosis.

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