What is the point: will screening mammography save my life?

Abstract

BackgroundWe analyzed the claim "mammography saves lives" by calculating the life-saving absolute benefit of screening mammography in reducing breast cancer mortality in women ages 40 to 65.MethodsTo calculate the absolute benefit, we first estimated the screen-free absolute death risk from breast cancer by adjusting the Surveillance, Epidemiology and End Results Program 15-year cumulative breast cancer mortality to account for the separate effects of screening mammography and improved therapy. We calculated the absolute risk reduction (reduction in absolute death risk), the number needed to screen assuming repeated screening, and the survival percentages without and with screening. We varied the relative risk reduction from 10%–30% based on the randomized trials of screening mammography. We developed additional variations of the absolute risk reduction for a screening intervention, including the average benefit of a single screen, as well as the life-saving proportion among patients with earlier cancer detection.ResultsBecause the screen-free absolute death risk is approximately 1% overall but rises with age, the relative risk reduction from repeated screening mammography is about 100 times the absolute risk reduction between the starting ages of 50 and 60. Assuming a base case 20% relative risk reduction, repeated screening starting at age 50 saves about 1.8 (overall range, 0.9–2.7) lives over 15 years for every 1000 women screened. The number needed to screen repeatedly is 1000/1.8, or 570. The survival percentage is 99.12% without and 99.29% with screening. The average benefit of a single screening mammogram is 0.034%, or 2970 women must be screened once to save one life. Mammography saves 4.3% of screen-detectable cancer patients' lives starting at age 50. This means 23 cancers must be found starting at age 50, or 27 cancers at age 40 and 21 cancers at age 65, to save one life.ConclusionThe life-saving absolute benefit of screening mammography increases with age as the absolute death risk increases. The number of events needed to save one life varies depending on the prospective screening subset or reference class. Less than 5% of women with screen-detectable cancers have their lives saved.

Promoting Screening Mammography: Insight or Uptake?

“…36 In comparison, columns C and D show the diagnosis risk for breast cancer and DCIS, 37 whereas column E shows the absolute death risk without screening mammography. 13 Barratt et al 38 show similar estimates for Australia. Without screening, over a decade a 50-year-old woman has a 5 times greater risk of receiving a diagnosis of breast cancer than of dying from it.…”

“…12 Therefore, the lowest life-saving proportion would be 3% (1/5 ϫ 1/7) in the larger subgroup of women who have been diagnosed with cancer. 13 The "pink ribbon" marketing 10,14 of breast cancer awareness supports advocacy groups and aims to increase the uptake of (participation in) mammography. Ostensibly for the sake of public health, the advertising campaign has some negative consequences.…”

“…She also has a 10 times greater risk of dying from something besides breast cancer. Table 2 derives estimates for the life-saving proportion of screen-detected cancers, the reciprocal or number needed to detect to save one life, 13 and the extent of overdiagnosis for US women.…”

Effectiveness of Mammography Screening in Reducing Breast Cancer Mortality in Women Aged 39–49 Years: A Meta-Analysis

“…3 Studies have shown that 90% of women surveyed considered screening important in early detection and reduction of breast cancer mortality. 4 In a recent study Davis et al, 5 compared national and state-based estimates for the prevalence of mammography screening from the National Health Interview Survey (NHIS) and the Behavioral Risk Factor Surveillance System (BRFSS). They reported that the prevalence rates of women receiving mammography screening within the past 2 years increased from 73% in the period 1997-1999 to 76.7% in the period 2000-2003 among women aged ‡ 40 years.…”

Factors related to non-adherence to mammography in a city of the Brazilian Amazonian area: A population-based study

“…[22][23][24] For younger women (< 50 years), the effectiveness of mammograms is controversial because it is related more with an increase in costs from unnecessary interventions than with reduced mortality. 25 During the agreement of the goals for the control of breast cancer in 2006, the Ministry of Health of Brazil recommended a biennial mammogram for women aged 50 to 69 years and an annual clinical breast examination for those aged between 40 and 49 years.…”