In Ireland, national guidelines call for women to begin routine screening mammograms at 35 years old. That’s too soon, according to the authors of a new analysis showing just 2.1 cancers per 1,000 symptomatic women aged 35 to 39 who were screened over a five-year period.

This rate is not only “below accepted international thresholds to undertake screening mammography” but also “raises radiation protection issues,” write Anne Buckley and colleagues at Trinity College Dublin and St. James’s Hospital Dublin.

“Additionally, a large number of benign biopsies were undertaken,” they add, “with likely resultant psychological impact.”

Their paper posted online Jan. 6 in Clinical Radiology.

Buckley and team retrospectively reviewed all mammograms performed on patients in the 35-39 age bracket at St James’s Hospital from 2011 to 2015. This starting number was 4,087 patient cases.

For their analysis, they excluded 2,148 patients because they had moderate or high familial risk of breast cancer, personal breast cancer history or chest radiation, males, general practitioner and internal hospital referrals, and women with abnormal clinical examinations.

They homed in on cases of women who had normal, benign or undocumented exam findings, recording the patients’ imaging and histopathological results and extracting related data from the hospital’s electronic record systems.

The researchers found that, of the 1,939 women in this included group, four (0.21 percent) were diagnosed with breast cancer as confirmed at histology based on mammographic findings. (Two patients had invasive ductal carcinoma; two had ductal carcinoma in situ).

Overall, 115 biopsies were performed in this cohort. Of these, 55 (47.8 percent) were attributable to mammographic screening, producing a biopsy rate of 2.8 percent due to mammography alone.

“This has cost and resource implications for service providers, and may have a psychological impact on the affected women,” Buckley et al. write in their discussion. “We suggest an age threshold revision to 40 years to guide routine evaluation of breast symptoms.”

The authors acknowledge their relatively small sample size as a limitation and call for further studies.

Across the pond in the U.S., the starting point for routine screening mammograms is perpetually contended. The U.S. Preventative Services Task Force recommends such screenings every other year from 50 to 74, with physician consultations from 40 to 49. Other groups offer similar but varying recommendations.