The idea that only women at increased risk should be screened in their 40s is an example of “risk-based screening.”
Since breast cancer is less common in the 40s than in older women, there are fewer cancers to be found. At the same time, largely because it may be the first time a woman has mammography screening, and also because the breasts are more often dense, there are more false positives (callbacks for additional testing when no cancer is found) in women in their 40s. In risk-based screening, the goal is to reduce the number of women who are screened or the frequency of screening or both.
However, if mammography screening were limited to only women with family history of breast cancer and/or dense breasts, most studies suggest that the majority of women diagnosed with cancer in their 40s would not be screened.
Several studies have examined how many cancers occur in women who would not be screened by “risk-based screening.” In the study of Destounis et al , 61% of women diagnosed with cancer in their 40s had no family history of breast cancer. In the study of Price et al , only 24% of women diagnosed with breast cancer in their 40s had a very strong family history of breast cancer (first degree relative diagnosed by age 50 or two first-degree relatives diagnosed) or extremely dense breasts. Some family history of breast cancer (first-degree relative diagnosed at any age) or dense breast tissue (including heterogeneously dense breast tissue) was present in 79% of women diagnosed with breast cancer. Neal et al  found only 20% of women diagnosed with breast cancer in their 40s had a family history of breast cancer.
The ongoing WISDOM Study  (Women Informed to Screen Depending On Measures of risk) randomizes consenting women to “adaptive screening.” In women who accept randomization, screening will commence for a woman in her 40s only when she has 5-year risk at least as high as an average 50-year-old woman (1.3% 5-year risk of developing breast cancer) and screening would then be biennial for most women and annual for women with extremely dense breasts or other risks. Burnside et al  evaluated cancer yield if screening were limited to those women in their 40s who had at least the same 5-year risk of breast cancer as a woman of age 50. They found that only 13/50 (26%) of cancers occurred in women who would have been screened based on risk. If screening were limited to women over age 45, 34/50 (68%) of cancers diagnosed in women in their 40s would have been found on screening.
- Breast cancer is the number one cause of death in women aged 35 to 54 years.
- Mammography has been proven to reduce deaths due to breast cancer in women screened beginning at age 40.
- Treatment is less invasive for women diagnosed by screening, including women diagnosed in their 40s .
- 25% of all years of life lost to breast cancer occur in women diagnosed before the age of 45.
Thus, under any scenario of restricting mammography screening in the 40s to only those women at increased risk, the cancer-detection benefits of screening are reduced.
All U.S. national medical societies agree that breast cancer screening beginning at the age of 40 saves the most lives. For more information about screening guidelines by medical society, click here.