Updated: Sunday, July 12, 2015, 3:01 AM
In the ongoing debate over the pros and cons of breast- cancer screening with mammograms, one of the hottest issues is overdiagnosis - and its potential dangers to women.
"Overdiagnosis is the diagnosis of a tumor that would not have become clinically apparent in the absence of screening," explains an editorial in last week's JAMA Internal Medicine. "Treatment of an overdiagnosed tumor cannot provide benefit, but it can lead to harm."
The editorial accompanies a new study that investigated the problem by using government data to correlate use of mammography in 547 U.S. counties with breast-cancer incidence and deaths over a decade.
As expected, the more screening, the more small breast cancers were found. Health campaigns say such early detection prevents more advanced tumors and, thus, deaths. But the study found that more mammography was not linked to reduced detection of larger cancers or lower death rates.
"Together, these findings suggest widespread overdiagnosis," says the study team, including Dartmouth Medical School physician H. Gilbert Welch, who has long warned about the dangers.
It is counterintuitive that finding and getting rid of cancer as early as possible is not always prudent. But treating a tumor that would never become a real threat poses real risks - pain, infections, anesthesia reactions, complications of surgery or radiation. There may be financial and sexual fallout.
Alas, acknowledging that some women wind up with unnecessary therapy is a long way from solving the dilemma. As University of Washington epidemiologist Joann G. Elmore says in the editorial, doctors can't distinguish which cancers can be safely left alone, or even say for sure what percentage are overdiagnosed.
So what's a health-conscious woman to do? Understanding the context of the debate may help.
Overdiagnosis errs on the side of caution
As technology and the science evolve, the downsides of being overcautious become clearer. Prostate cancer screening with the PSA test - once hailed as a breakthrough - is no longer recommended by many expert groups, notably the government's influential U.S. Preventive Services Task Force (USPSTF), because early detection saves few if any lives, and treatment often leaves men with permanent sexual and urinary problems.
"Overdiagnosis is a reality of preventive care," said Thomas Jefferson University family physician Richard Wender, chief cancer control officer of the American Cancer Society. "It's an advance to recognize that it occurs, and to inform patients about it."
Mammography isn't perfect, but it works.
Unlike the PSA test, mammography has been definitively shown by studies to reduce breast-cancer mortality about 20 percent among women ages 40 to 74. Though modest overall, this mortality benefit increases as women age and have a higher risk of breast cancer, so the USPSTF recommends biennial screening for women ages 50 to 74.
The American Cancer Society is among groups that recommend screening starting at age 40, but a review is underway to see whether to change this advice, Wender said.
Risk is partly about perception and values.
The lifetime risk of invasive breast cancer is now 12.5 percent, about 1 in 8, according to the U.S. Centers for Disease Control and Prevention. Turned around, that's an 87.5 percent chance, or 7 in 8, of never getting cancer. Interactive "decision aids" are now available that help patients make choices based on individual preferences. (For a breast-cancer-screening decision aid, see http://bsd.med.cornell.edu.)
A recent study led by biologist Winnifred Cutler, founder of the Athena Institute for Women's Wellness in Chester Springs, focused on the risk for women who are near or past menopause - when most breast cancer is diagnosed. To eliminate what Cutler sees as flaws in the CDC's estimates, her team analyzed data from 19 existing studies of more than 2.3 million women. They concluded that only 5 percent of screened women will be diagnosed over 25 years. (The CDC estimate is 7.2 percent.)
The biology of cancer remains mysterious.
Some experts say breast-cell abnormalities confined to the milk ducts, called ductal carcinoma in situ (DCIS), shouldn't even be called cancer because it often doesn't invade nearby tissue. Overdiagnosis of DCIS, experts agree, is more common than with invasive breast cancer.
Conversely, some aggressive breast cancers may be lethal, despite early detection and treatment, because they have already metastasized, or spread.
Welch uses the metaphor of trying to keep turtles, rabbits, and birds from escaping a fenced pen. The turtles aren't leaving, and the birds are unstoppable; only the rabbits can be deterred.
The debate arouses emotion and bias.
Cutler, who sells pheromone products that she says are scientifically shown to increase sexual attractiveness, believes healthy women with no history or symptoms of breast cancer should reject screening altogether.
Welch, whose books include Overdiagnosis: Making People Sick in the Pursuit of Health, does not believe "the right rate of screening is zero." But he advocates "watchful waiting" rather than immediate treatment of DCIS.
Catherine Tuite, a Fox Chase Cancer Center radiologist specializing in breast cancer, countered: "I've never met a woman who was newly diagnosed who says, 'It's OK. I'll just watch and wait.' "
She added, "There has been a 30-year effort to deny women access to screening mammography, and it has created fear and confusion."
The JAMA Internal Medicine editorial sought a middle ground: "We need to learn how to communicate with our patients about uncertainty and the limits of our scientific knowledge."
Read full story: When mammograms are more harm than help