The probability that screening mammography saved a woman’s life is less than 25 percent, according to an article published Oct. 24 in the Archives of Internal Medicine. The accompanying commentary advocated for clinicians to share a simple scientific message that does not inflate the survival benefit of screening mammography.
Given the promulgation of survival stories stating that screening “saved my life,” researchers sought to estimate the probability that a woman with screen-detected breast cancer has had her life saved because of screening.
H. Gilbert Welch, MD, MPH, and Brittney A. Frankel, both of the Dartmouth Institute for Health Policy and Clinical Practice in Hanover, N.H., offered an alternate interpretation of survivor stories crediting screening mammography as a life-saving exam.
They noted that screening-detected breast cancer may have been equally treatable if it had presented clinically. Alternately, screening-detected breast cancer may have been overdiagnosed; that is, the disease may not cause symptoms or death.
The researchers used DevCan, the National Cancer Institute’s software for analyzing Surveillance Epidemiology and End Results, to estimate the 10-year risk of breast cancer diagnosis and the 20-year risk of breast cancer death for women age 40, 50, 60 and 70 years. Welch and Frankel assumed that screening reduced the risk of breast cancer death by 20 percent and estimated the probability that a 50-year-old woman with screen-detected breast cancer avoided death by screening mammography at 13 percent.
Welch and Frankel tested various scenarios based on age and mortality reduction and each yielded probability estimates below 25 percent.
The researchers acknowledged several limitations to the methods. They assumed that the burden of disease remained stable over time and applied a 10-year mortality benefit to the screening period.
They noted the most consequential variable in the analysis is the relative risk reduction (RRR) attributable to screening mammography. Higher end values in the 20 to 25 percent range, they wrote, “reflect the randomized trial data from more than a quarter century ago.”
Welch and Frankel suggested that the mortality benefit has declined over time and attributed this reduced benefit to two factors: the benefit of screening is reduced as women with breast lumps present earlier for evaluation and treatment of clinically detected breast cancer has improved.
“Consequently, we believe that readers should focus on the values toward the low end (5 to 10 percent) and recognize the probability that a woman with screen-detected breast cancer has, in fact, avoided a breast cancer death because of screening mammography is now likely to be well below 10 percent.”
Welch and Frankel added that the increasing resolution of mammographic imaging has aggravated the issue of overdiagnosis by detecting cancers that would not cause symptoms or death.
The researchers concluded, “A woman with screen-detected cancer is considerably more likely not to have benefited from screening.”
In the accompanying invited commentary, Timothy J. Wilt, MD, MPH, and Melissa R. Partin, PhD, cautioned of the dangers of “a self-perpetuating cycle of unwarranted demand for screening, overdiagnosis, overtreatment and continually growing population of breast cancer survivors who advocate mammography.”
The editorialists advised clinicians not to use personal survival narrative in their screening recommendations as they are prone to distortion and misinterpretation and urged a simple message recommending biennial screening for women age 50 to 74 years. They also suggested that physicians advise women age 40 to 50 years and those older than 74 years about the harms of overdiagnosis.
Wilts and Partin noted that problems with preventive screening extend beyond mammography and include:
- Routine spirometry to detect chronic obstructive pulmonary disease, measuring ankle-brachial artery blood pressure and conducting carotid artery ultrasound to detect peripheral and carotid artery disease;
- Performing CT to detect coronary heart disease risk;
- Evaluating coronary artery stenosis severity; and
- Lowering threshold and broadening population applications for detecting and treating osteoporosis.