"Lead-time" bias can also contribute to misrepresentation of mammography's advantages, according to the National Breast Cancer Coalition (NBCC), a group of patient and professional organizations.

This means, for example, if deadly cancer is found early through screening, it may seem like the patient lived longer because of "lead-time." But the coalition says this makes screening appear more beneficial than it is, because testing is actually detecting tumors that have a better prognosis.

"NBCC believes that there is insufficient evidence to recommend for or against universal screening mammography in any age group of women," according to the organization's website.

"Women who have symptoms of breast cancer such as a lump, pain or nipple discharge should seek a diagnostic mammogram. The decision to undergo screening for asymptomatic women must be made on an individual level based on a woman's personal preferences, family history and risk factors.

"Mammography does not prevent or cure breast cancer, and has many limitations," the website says. "Women are told that mammography screening saves lives, but the evidence of a mortality (death rate) reduction from screening is conflicting and continues to be questioned by some scientists, policy makers and members of the public."

Dr. Otis Brawley, chief medical officer of the American Cancer Society, said he understands Woloshin and Schwartz's message.

"It is very, very difficult to convey information about screening, especially mammography, and convey it accurately," Brawley told CNN.

"In the American Cancer Society's screening recommendations, the first paragraph recommends women over the age of 40 get a mammogram annually. The second paragraph says that women should be told the limitations of screening. ... Some of the folks at Komen are trying to do the right thing, and I just respect how difficult that is."