Mammographically detected tumors display better survival prognosis

Women with mammographically detected tumors live longer than women who have had their tumors detected via alternative methods, according to researchers at the University of Texas M.D. Anderson Cancer Center.

"One might think that a tumor is a tumor is a tumor. Not so. A woman with a mammographically detected tumor that is otherwise indistinguishable from one detected in some other way turns out to have a substantially better prognosis," said coauthor Donald Berry, Ph.D., chair of the biostatistics and applied mathematics department at the center.

The "stage shift" associated with screening mammography, in which early-stage tumors represent a higher proportion of tumors detected mammographically, means that women with mammographically detected tumors live longer than women whose tumors were detected otherwise, according to Berry.

Berry and colleagues took into account the stage shift phenomenon by comparing women with tumors of the same stage but detected using different methods. The study was published in the August 17 issue of the Journal of the National Cancer Institute.

The investigators examined data from three large breast cancer screening trials: the Health Insurance Plan (HIP) of New York as well as two Canadian National Breast Cancer Screening Studies (CNBSS).

They randomly assigned 62,000 women from the HIP program into screening and control groups. From the combined CNBSS trial cohorts, they assigned 44,970 women to the screening group and 44,961 women to a control group.

When the data from all of the groups had been adjusted for stage and additional tumor characteristics, such as size, lymph node status, and disease stage, the researchers reported that screening mammography was a significant predictor of survival.

Patients with interval cancers had a 53% greater hazard of death from breast cancer than patients with screen-detected cancers. Women with cancer in the control groups had a 36% greater hazard of death than patients with screen-detected cancer.

Despite these promising results, Berry said that researchers need to be able to better assess a tumor's future development.

"Tumors detected mammographically tend to be slower growing than those detected otherwise. But we are not yet very adept at distinguishing the slowly growing, indolent tumors from the fast-growing, aggressive ones," he said. "Someday that will change, and we'll be able to dissect a tumor molecularly and accurately assess its metastatic potential."