Advanced, Fatal Breast Cancers Reduced Through Mammography Screening

For prevention of breast cancer among women in Sweden, mammography screening is recommended every 18 months for ages 40 to 54 years and every 2 years for ages 55 to 69 years. Recent results on 10-year mortality from the disease, published in Cancer, from the American Cancer Society, show the success of participating in the screening in the country for both of these age groups, emphasizing the importance of early detection.

“Some may believe that recent improvements in breast cancer treatment makes early detection less important," said László Tabár, MD, of Falun Central Hospital, Sweden. "Our study shows that nothing can replace finding breast cancer early."

The Swedish Cancer Registry provided the study team with patient data on breast cancer diagnoses, and The Swedish Cause of Death Register of the Swedish National Board of Health and Welfare supplied the causes and dates of death for the 549,091 patients followed for the study, or almost 30% of the population eligible for screening.

For the purposes of their study, the team used the following 2 definitions:

1. A diagnosis of advanced breast cancer was defined by invasive disease involving tumors larger than 20 mm and/or involvement of at least 4 metastatic axillary lymph nodes.
2. Women were considered as having participated in mammography screening if she kept her most recent appointment for the procedure.

Women in the study with fatal disease were followed for an average of 13 (range 7-16) years and those with advanced disease, 22 (range 16-25) years. There were 2473 (.45%) cases of fatal disease and 9737 (1.8%) cases of advanced-stage disease.

Overall, in the 10 years following a diagnosis that resulted from a screening mammography, the relative risk (RR) of cases of fatal breast cancer came in at 0.59 (95% CI, 0.51-0.68; P <.001). This equates to a 41% reduction in cases resulting in death from the disease. The conservative estimate was still significant, at 34% (RR, 0.66; 95% CI, 0.55-0.79; P <.001). For advanced breast cancers, the RR was 0.75 (95% CI, 0.66-0.84; P <.001), or a 25% decrease in these diagnoses over the 10 years.

The authors underscore the important of their findings in light of their study’s strengths. Namely its large patient population, statistical precision, and long-term follow-up. However, they also caution interpretation of the results, based on lack of data on mammography screenings from private facilities.

To continue to see positive results from early detection of breast cancer, the team of researchers emphasize the importance of continuing to collect data on nationwide screening rates for the disease, for all methods, not just mammography. These data should be used to evaluate each of these methods, especially newer techniques.

“Our evaluation of outcomes demonstrated that women who attended screening, and typically had their breast cancer diagnosed at an earlier stage, benefited substantially more from the state-of-the-art therapy existing at the time of diagnosis and over the period of our analysis compared with women who did not attend screening,” noted the authors.” Detection at an earlier stage through participation in mammography screening confers a significant reduction in the risk of death from breast cancer in this era when modern adjuvant therapies are available.”

Reference

Duffy SW, Tabár L, Yen AM-F, et al. Mammography screening reduces rates of advanced and fatal breast cancers: results in 549,091 women [published online May 11, 2020]. Cancer. doi:10.1002/cncr.32859