Second -- and here's where the risks of screening really come in -- it can detect something that isn't disease. "When we find something solid, that is automatically considered suspicious and needs a biopsy," Wallace says.
The procedure entails removing tissue or fluid from the lump. But the problem doesn't end there. Beyond the biopsy, sometimes women end up being treated for cancers that would never have become aggressive and threatened their lives.
Biopsies can also find atypical cells that are considered precancerous. "Sometimes, diagnosing these precancerous conditions results in more women doing something very aggressive just to reduce their anxiety about developing breast cancer," Hwang says. She has had patients who had elective bilateral mastectomies after precancers were found, rather than face the risk of developing a full-blown cancer.
The task force calculated that among women in their 40s, 1,900 must be screened to save one life. They also cite studies that estimate the risk of getting a false positive scan after 10 mammograms as ranging from 21% to 56%.
Balancing those harmed with those saved leaves physicians with a dilemma. "It gets down to how many women is it OK to [have] die -- this is what's heartbreaking to me," Wallace says. "I've always known we're not meeting big statistics in this age group, but we definitely are saving some lives."
If doctors can't make up their minds about screening, how can women?
Some doctors say they will take advantage of the current dust-up to have careful conversations with their patients about the risks and benefits of screening in the context of patients' own risk profiles.
"I think that should happen anyway," Wallace says. "A check-off system of 'Are you getting all your screenings?' shouldn't be the way primary care practices."
To learn more about factors that determine a woman's individual risk of breast cancer, go to the National Cancer Institute, which has a breast cancer risk assessment tool (www.cancer.gov/bcrisktool) and a mammogram fact sheet (www.cancer.gov/cancertopics/factsheet/Detection/mammograms).