Age-specific differences in mammographic screening can contribute to lower detectability and differences in tumor growth rates, according to a study published online July 27 in the Journal of the National Cancer Institute.
Stephanie L. Bailey, PhD, and colleagues of the department of radiology at the Stanford University School of Medicine in Palo Alto, Calif., compared women between the ages of 50-69 years to women between the ages of 40-49 years in order to observe the lower sensitivity and reduced effectiveness of mammographic screening in younger women, which has been attributed to the lower mammographic tumor detectability and faster tumor growth in the younger women.
The researchers utilized a breast cancer screening simulator to create hypothetical screening scenarios in order to estimate the average tumor size detectable on a mammogram and the average tumor volume doubling time. By way of the Surveillance, Epidemiology and End Results (SEER) database and the Breast Cancer Surveillance Consortium, the estimates were calculated by calibrating the predicted breast cancer incidence rates to the actual rates and the predicted distributions of screen-detected tumor sizes to the actual distributions.
Mammography screening outcomes included sensitivity, mean tumor size at detection, lifetime gained and breast cancer mortality. These estimations were utilized by the authors to approximate relative impact of lower mammographic tumor detectability compared to faster tumor volume doubling time on the poorer screening outcomes in younger women compared with older women.
Bailey and her colleagues also investigated the relationship between screening sensitivity and breast cancer mortality as a function of tumor volume doubling time, mammographic tumor detectability and screening interval.
The researchers found that lowered mammographic tumor detectability accounted for 79 percent and faster tumor volume doubling time accounted for 21 percent of the poorer sensitivity of mammography screening in younger women compared with older women. In addition, screening sensitivity and breast cancer mortality reduction attributable to screening were almost linearly related when comparing annual or biennial screening with no screening.
Moreover, when comparing annual with biennial screening, the greatest reduction in breast cancer mortality attributable to screening did not correspond to the greatest gain in screening sensitivity and was more strongly affected by the mammographic tumor detectability than tumor volume doubling time, they wrote.
“The age-specific differences in mammographic tumor detection contribute more than age-specific differences in tumor growth rates to the lowered performance of mammography screening in younger women,” Bailey and colleagues offered.
“More research is needed to not only establish a better relationship between mammographic breast density and breast cancer risk but also understand the differences in tumor characteristics in dense versus non-dense breast tissue," the study concluded.