Women who skipped one or both scheduled mammography appointments immediately prior to a breast cancer diagnosis had a significantly higher risk of dying of the disease, a large retrospective analysis showed.
Women who kept both appointments had about a 50% lower 10-year and overall risk of breast cancer death as compared with women who skipped both examinations. Showing up for either of the mammography appointments lowered the risk of developing fatal breast cancer as compared with missing both examinations, but the patients remained at significantly greater risk as compared with the patients who kept both appointments.
The findings highlight not only the risk-reducing benefits of mammography but the hazards of interval-detected (between mammography exams) breast cancers, stated Stephen W. Duffy, MSc, of Barts and the London School of Medicine, and colleagues in Radiology.
"While we suspected that regular participation would confer a reduction greater than that with irregular participation, I think it is fair to say that we were slightly surprised by the size of the effect," Duffy said in a statement. "The findings support the hypothesis that regular attendance reduces the opportunity for the cancer to grow before it is detected."
More Food for Thought
The findings added more food for thought to the ongoing controversy about the age at which women begin mammography, how often they should have exams, and at what age they can safely discontinue mammography. Studies dating back at least 30 years have shown that women with breast cancer live longer if they had a recent mammogram, as compared with women who did not participate in screening, the authors noted. Additionally, women who did not participate in screening had worse breast cancer outcomes as compared with the general population.
A report from a British breast cancer screening program showed better breast cancer survival in patients with lapsed mammography (three years removed from last negative exam) than in women who did not participate in screening. Case-control studies of breast cancer mortality showed a lower mortality among women who had participated in screening, but the benefit decreased as the time since the last mammogram increased.
Duffy and colleagues hypothesized that participation in serial mammographic screening would reduce the risk of dying of breast cancer as compared with irregular participation, and that irregular participation in screening would reduce breast cancer mortality as compared with non-participation.
Data for the analysis came from a Swedish death registry for a nine-county area and from regional oncology centers in the area. The study involved breast cancer diagnoses and deaths from 1992 to 2016. During that period, screening mammography was recommended every 18 months for women, ages 40 to 54, and every 24 months for women ages 55 to 69. Participation in screening across the study area ranged from about 70% to 90%.
Investigators defined four categories of screening participation: serial participants (attended the last two scheduled screening exams before breast cancer diagnosis), intermittent (participated in the last but not the next-to-last scheduled exam), lapsed (participated in the next-to-last exam but not the last exam), and serial nonparticipants (missed the last two screening exams before diagnosis).
The primary objectives were to estimate the effect of different screening participation patterns on breast cancer mortality and on the incidence of breast cancers that proved fatal within 10 years of diagnosis.
The analysis included 549,091 women who had a mean age of 58.9. The study population consisted of 392,135 serial mammography participants, 41,746 intermittent participants, 30,945 lapsed participants, and 84,265 serial nonparticipants. The study had a mean follow-up of 22 years for mortality and 13 years for breast cancers that proved fatal within 10 years after diagnosis.
Screening Saved Lives
A total of 3,995 breast cancer deaths occurred during the observation period, including 2,589 cancers that proved fatal within 10 years of diagnosis. Serial mammography participation was associated with a 49% reduction in the relative risk of breast cancer mortality as compared with serial nonparticipants (95% CI 0.48-0.55, P<0.001). The benefit declined to 33% for intermittent participation (95% CI 0.59-0.76, P<0.001) and 28% for lapsed participation (95% CI 0.63-0.83, P<0.001).
Serial participants had a 23% lower risk of breast cancer death versus intermittent participants (95% CI 0.69-0.86, P<0.001) and a 30% lower risk compared with lapsed participants (95% CI 0.61-0.80, P<0.001). Breast cancer mortality did not differ significantly between intermittent and lapsed participants.
With respect to breast cancer death within 10 years of diagnosis, the rate was 50% lower in serial participants versus serial nonparticipants (95% CI 0.46-0.55, P<0.001). Intermittent and lapsed participation was associated with reductions of 36% and 25%, respectively, both of which achieved statistical significance (P<0.001). Serial participants had a 22% risk reduction versus intermittent participants and a 33% reduction compared with lapsed participants (P<0.001). The 10-year breast cancer mortality did not differ between intermittent and lapsed participants.
The results are consistent with those of a smaller study from Massachusetts General Hospital in Boston, and the message from both studies is straightforward, according to Laurie Margolies, MD, of Mount Sinai Medical Center in New York City.
"Screening mammography saves lives. However, to get the most benefit from screening you need to get regular yearly mammograms," she told MedPage Today via email. "One mammogram is not sufficient. Once-in-a-while mammography is not sufficient if your goal is to decrease the chances that you will die from breast cancer.
"If you miss even one yearly mammogram the chances of dying from breast cancer increase. This is very important in the setting of the current pandemic where many women have missed their 2020 mammograms," Margolies stressed.
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Disclosures
The study was supported by the American Cancer Society and Bröstcancerförbunder, Sweden.
Duffy disclosed no relevant relationships with industry. Co-authors disclosed relevant relationships with GE Healthcare and Three Palm Software.
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