In the Journals

Biennial mammograms from age 50 years reduce risk for radiation-induced breast cancer

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January 14, 2016

Biennial mammography screening starting at age 50 years appeared to reduce the risk for radiation-induced breast cancer and breast cancer death compared with annual screening from age 40 years, according to results of a modeling study.

Results showed radiation dose variability, resultant diagnostic workup, initiation age and screening frequency all affect the incidence of radiation-induced breast cancer. Further, women with large breasts appeared to have a greater risk for radiation-induced breast cancer.

Diana L. Miglioretti

Diana L. Miglioretti

“In general, the risk for a radiation-induced breast cancer from mammography screening is very low,” Diana L. Miglioretti, PhD, a professor of biostatistics in the department of public health sciences in the school of medicine at University of California, Davis, told HemOnc Today. “We found that risks were highest for women with large breasts who require additional mammography views for complete breast examination, especially if they are screened annually starting at age 40. Biennial screening from ages 50 to 74 reduced risks fivefold compared with annual screening from ages 40 to 74.”

These data are in line with the recent statement update issued by the U.S. Preventive Services Task Force that recommends commencing biennial mammography at age 50 years.

Miglioretti and colleagues evaluated radiation exposure and dose variation from screening and additional diagnostic measures to estimate the distribution of radiation-induced breast cancer incidence and mortality.

Researchers used two stochastic modeling approaches — the Microsimulation of Screening Analysis-Fatal Diameter and a new radiation exposure simulation model — to simulate mammography events associated with radiation exposure and outcomes for a population adherent to eight screening strategies. These strategies included annual screening from age 40 to 74 years, 45 to 74 years or 50 to 74 years; biennial screening from age 40 to 74 years, 45 to 74 years or 50 to 74 years; or a hybrid approach of annual screening from age 40 to 49 years or 45 to 49 years followed by biennial screening from age 50 to 74 years.

Researchers derived population-based data from the Breast Cancer Surveillance Consortium to estimate the probability of a false-positive screening followed by additional imaging evaluation, short-interval follow-up or biopsy.

Overall, annual screening of 100,00 women aged 40 to 74 years was projected to lead to 125 (95% CI, 88-178) breast cancer cases, resulting in 16 (95% CI, 11-23) deaths, whereas 968 breast cancer-related deaths would be averted due to early detection from screening.

Women exposed to radiation at the 5th percentile were projected to develop 64 (95% CI, 44-90) radiation-induced breast cancer cases leading to eight (95% CI, 6-12) deaths per 100,000 women, whereas women exposed to radiation at the 95th percentile were projected to develop 246 (95% CI, 171-349) cases of radiation-induced breast cancer leading to 32 (95% CI, 22-45) deaths per 100,000 women.

Women with large breasts made up 8% of the population and were exposed to 1.8 times more radiation. Those who required extra views for complete examination had twice as many cases of radiation-induced breast cancer — with a projected 266 cases (95% CI, 186-380) and 35 deaths (95% CI, 24-50) per 100,000 women — compared with women with small or average-sized breast (113 cancer cases; 95% CI, 79-161; 15 deaths; 95% CI, 10-21).

Biennial screening starting at age 50 years was projected to reduce the risk for radiation-induced breast cancer approximately fivefold per 100,000 women (mean, 125 cases; 95% CI, 88-178 vs. mean, 27 cases; 95% CI, 19-38).  This trend persisted among women with large breasts (mean, 266 cases; 95% CI, 186-380 vs. mean, 57 cases; 95% CI, 40-82).

“We found that women with additional work-up of a positive mammogram including diagnostic mammography, image-guided biopsies, and/or short-interval follow-up exams have about double the radiation exposure, on average,” Miglioretti said. “Thus, reducing false-positive mammograms will reduce radiation-induced breast cancer risk.”

There is some evidence to suggest 3-D mammography could reduce false-positive mammograms, Miglioretti added.

“However, to reduce radiation exposure, it is important that tomosynthesis be used with synthetic 2-D views instead of being done in addition to 2-D digital mammography,” she said. “Otherwise, radiation exposure from the screening exam, and radiation-induced breast cancer risk, is more than doubled.”

Researchers acknowledged they could not estimate life years lost from radiation-induced breast cancer. Further, they could not model the association between breast size and the probability of a false-positive result, which could have led to an underestimation of exposure from additional work-up in women with large breasts because obese women are 20% more likely to have a false-positive result.

“As a next step, we would like to evaluate how mammographic breast density influences radiation-induced breast cancer risk given radiation dose delivered from digital mammography increases with breast density and having dense breasts increases a woman’s risk for a false-positive mammogram,” Miglioretti said. – by Anthony SanFilippo

For more information:

Diana L. Miglioretti, PhD, can be reached at dmiglioretti@ucdavis.edu.

Disclosure: Miglioretti reports no relevant financial disclosures. Please see the full study for a list of the other researchers’ relevant financial disclosures.

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