A longitudinal study involving 90,000 women casts doubts on the value of mammography screening for breast cancer detection.

The study found that death rates from breast cancer between women who received annual mammograms and those who didn't, making up the control group, was not significantly different. The study also found that mammograms caused harm to one of five women in the mammogram receiving group. Their overdiagnoses lead to unneeded treatment such as chemotherapy, surgery or radiation.

"Annual mammography in women aged 40-59 does not reduce mortality from breast cancer beyond that of physical examination or usual care when adjuvant therapy for breast cancer is freely available.Overall, 22 percent (106/484) of screen detected invasive breast cancers were over-diagnosed, representing one over-diagnosed breast cancer for every 424 women who received mammography screening in the trial," concluded the study, which was published in The British Medical Journal.

The researchers found that there was no benefit to detecting tumors that are too small to feel, and thus requiring a mammogram to detect, according to researchers, as reported by the New York Times.

"The study seems likely to lead to an even deeper polarization between those who believe that regular mammography saves lives, including many breast cancer patients and advocates for them, and a growing number of researchers who say the evidence is lacking or, at the very least, murky," writes the NY Times.

"It will make women uncomfortable, and they should be uncomfortable," Dr. Russell P. Harris, a screening expert and professor of medicine at the University of North Carolina, Chapel Hill, who was not involved in the study, told the NY Times. "The decision to have a mammogram should not be a slam dunk."