The world's largest breast cancer charity is misleading people about the benefits of mammography, according two experts from the Dartmouth Institute for Health Policy and Clinical Practice in New Hampshire.

The US-based Susan G. Komen for the Cure Foundation, which collaborates with breast cancer charities around the world, including the Canadian Breast Cancer Foundation, "overstates" how effective mammograms are and ignores the harm they cause, say professors Lisa Schwarz and Steven Woloshin, who co-authored an article on the subject in the British Medical Journal.

The charity strongly encourages women to get screened, because early detection of the disease is the key to surviving breast cancer - typically measured using a five-year survival rate.

But Schwarz and Woloshin say the figures the Komen foundation uses are flawed.

If 100 women are diagnosed at age 67 and all die at age 70, the five-year survival rate is 0%. But if they were diagnosed at age 64 and died at age 70, their five-year survival rate is 100% - even though none of them lived any longer.

"If there were an Oscar for misleading statistics, using survival statistics to judge the benefit of screening would win a lifetime achievement award hands down," they write.

Mammography only reduces the chance that a woman in her 50s will die from breast cancer over the next 10 years from 0.53% to 0.46%, a difference of 0.07 percentage points, the professors said.

Furthermore, overdiagnosis (detecting cancers that won't kill or even cause symptoms during a patient's lifetime) means many women are unnecessarily getting chemotherapy, radiation, surgery or other treatments, which are likely to harm their health.

The Breast Cancer Awareness Month campaign by the Komen foundation "undermined decision-making by misusing statistics to generate false hope about the benefit of mammography screening," the researchers said.

A spokeswoman for the Komen foundation agreed that mammography isn't perfect but said it's the best widely available detection tool available right now.

"The numbers are not in question," Chandini Portteus said in an e-mail to QMI Agency. "Early detection allows for early treatment, which gives women the best chance of surviving breast cancer."

Portteus also said the foundation recognizes that "science has to do better," and that it is funding research into alternative methods for detecting and assessing tumours.

"While we invest in getting those answers, we think it's simply irresponsible to effectively discourage women from taking steps to know what's going on with their health," she said.