Findings from a new national study has widened the clinical – and emotional – divide over the use of mammography in diagnosing breast cancer and its value in reducing the rate of death from the disease.

The observational study, published in Nov. 22 issue of the New England Journal of Medicine, examined more than 30 years of mammography and found its use has resulted in “a substantial over-diagnosis” of breast cancer. Further, the study found that mammography screening “is having, at best, only a small effect on the rate of death from breast cancer.”

Conducted by Dr. Archie Blyer of the St. Charles Health System in Oregon and Dr. H. Gilbert Welch of the Dartmouth Institute for Health Policy & Clinical Practice in New Hampshire, the study used 32 years, from 1976 to 2008, of breast-cancer data from the National Cancer Institute’s Surveillance, Epidemiology and End Results program to evaluate the efficacy of breast mammograms.

What these data findings suggest about the benefit of mammography screening is damaging, according to Welch. “If it does not advance the time of diagnosis of late-state cancer, it won’t reduce mortality,” Welch wrote in a New York Times opinion piece on Nov. 21. “In fact, we found no change in the number of women with life-threatening, metastatic breast cancer.”

The study’s findings are in concert with controversial guidelines issued by the U.S. Preventive Services Task Force in 2009 that recommended women over the age of 50 have mammograms every other year, instead of annual screenings starting at the age 40.

Those controversial guidelines, however, have not been adopted by Rhode Island’s two largest hospital systems, Lifespan and Care New England. Instead, both hospital networks have adhered to the guideline recommendations that women have yearly breast-cancer screenings with mammography beginning at age 40, as recommended by the American Cancer Society.