What are the risks in having a mammogram and am I stupid not to have one

The short version: mammography trades a small radiation risk and a large overdiagnosis risk for a modest reduction in breast cancer death, and the balance is worse for younger women.

The main risks are radiation, false alarms, and overdiagnosis. A 2014 study estimated that biennial screening from age 50 to 69 causes about 10 radiation-induced breast cancers per 100,000 women screened, and about 1 death from those cancers [4]. That same study estimated about 350 breast cancer deaths prevented per 100,000 screened [4]. So the radiation risk is real but small compared to the benefit for women over 50. For younger women, especially those under 40 or with BRCA mutations, the risk is higher. A 2017 systematic review found that BRCA carriers show exaggerated DNA damage from mammography-level doses and recommended cautious use of mammography in that group, with MRI as an alternative [1].

The bigger problem is overdiagnosis. Screening finds cancers that would never have caused symptoms or death. The Canadian National Breast Screening Study found that for women who started screening at age 40 to 49, the overdiagnosis rate reached about 55% when including ductal carcinoma in situ (DCIS) [12]. That means more than half of the cancers found in that group were overdiagnosed. For women starting at age 50 to 59, the overdiagnosis rate was about 16% [12]. A separate analysis of the same trial found that for every 2,000 women invited for screening over 10 years, 1 breast cancer death was prevented while 10 healthy women were treated unnecessarily [9]. The Cochrane review behind that number also found 31% more lumpectomies and mastectomies in the screened group [9].

You are not stupid to skip mammograms. The evidence shows a real but modest benefit for women over 50, and a much weaker case for women under 50. The randomized trials for women aged 40 to 49 show relative risk reductions for breast cancer death ranging from 0.52 to 1.03, and none of the individual trials reached statistical significance [7]. The Canadian trial for that age group found a relative risk of 0.97, meaning essentially no benefit [7]. The false-positive rate is also higher in younger women: about 6.7% recall rate for women 40 to 49 versus 4.2% for women over 50 [11].

My call: for a woman over 50 with average risk, mammography offers a modest net benefit, but the overdiagnosis problem is real and the decision is a legitimate trade-off. For a woman under 50, the evidence for benefit is weak and the harms are larger, and skipping screening is a reasonable choice. Confidence: moderate.