Whether breast cancer is detected during screening mammograms or detected in other ways may help define a woman's prognosis, according to a new study.

Screening mammography detects breast cancers at an earlier stage of development than breast cancers detected symptomatically – the so-called stage shift – and so mammographically detected breast cancers tend to have better prognoses. This stage shift is subject to various biases, so that earlier detection may not translate into lower mortality. In addition, screen-detected cancers tend to grow more slowly than cancers detected in other ways, which may also affect survival.

To examine the prognostic value of the method of breast cancer detection on survival, Donald A. Berry, Ph.D., of the University of Texas M. D. Anderson Cancer Center in Houston, and colleagues used data from three large North American randomized controlled trials of breast cancer screening. In all three trials, the authors found that after adjusting for tumor size, lymph node status, and disease stage, clinically detected cancers were associated with a 53% greater hazard of death from breast cancer compared with screen-detected cancers.

In an editorial, Ian F. Tannock, M.D., Ph.D., and Monika K. Krzyzanowska, M.D., of Princess Margaret Hospital in Toronto, discuss these results and those of another recent study, both of which reported better survival associated with screen-detected cancers. They conclude, however, that knowing the method of detection might add only limited prognostic value beyond that of well-established prognostic factors.

SOURCE:
Journal of the National Cancer Institute, August 17, 2005