In a Canadian study reported in the Journal of Clinical Oncology, Wilkinson et al found that breast cancer screening was associated with greater 10-year breast cancer net survival among women aged 40 to 49 living in jurisdictions including mammography screening programs for this age group, compared with women aged 50 to 59 in jurisdictions that do not include screening in this age group. The incidence of breast cancer diagnosis in the 40- to 49-year age group did not differ in the two types of jurisdictions.
As noted by the investigators: “In Canada, some provincial/territorial mammography screening programs include women aged 40 to 49 years, whereas others do not. This study examines the impact of this dichotomy on the 10-year breast cancer net survival among women aged 40 to 49 years and 50 to 59 years at diagnosis.”
Study Details
The study involved data from the Canadian Cancer Registry linked to death information for Canadian women aged 40 to 49 and 50 to 59 diagnosed with breast cancer from 2002 to 2007. The study compared 10-year net survival estimates in jurisdictions with organized screening programs that included women aged 40 to 49 (Northwest Territories, British Columbia, Alberta, Nova Scotia, and Prince Edward Island) with comparator programs that did not include this age group (Yukon, Manitoba, Saskatchewan, Ontario, Quebec, New Brunswick, Newfoundland, and Labrador).
Key Findings
Among women aged 40 to 49 diagnosed with breast cancer, that disease was the primary cause of 10-year mortality, accounting for 90.7% of deaths. Among these women, the 10-year net survival was 84.8% (95% confidence interval [CI] = 83.8%–85.8%) among screeners vs 82.9% (95% CI = 82.3%–83.5%) among comparators (difference = 1.9 percentage points, P = .001). By subgroups, a significant difference in favor of screeners was observed among those aged 45 to 49 (difference = 2.6 percentage points, P = .001) but not among those aged 40 to 44 (difference = 0.9 percentage points, P = .328).
The incidence-based breast cancer mortality rate was significantly lower among screeners vs comparators among women aged 40 to 49 at diagnosis (rate ratio [RR] = 0.92, 95% CI = 0.85–0.99) and among those aged 45 to 49 (RR = 0.89, 95% CI = 0.81–0.98) but not among those aged 40 to 44 (RR = 0.95, 95% CI = 0.85–1.07).
No difference in age-specific breast cancer incidence rates was observed among women aged 40 to 49 in screener vs comparator jurisdictions (133.1 cases per 100,000 women in both, P = .976), but the rate was significantly higher for comparators among those aged 50 to 59 (238.4 vs 217.6 cases per 100,000 women, P < .001).
The investigators concluded: “Screening programs that included women in their 40s were associated with a significantly higher [breast cancer] 10-year [net survival] in women aged 40 to 49 years, but not an increased rate of [breast cancer] diagnosis. These results may inform screening guidelines for women aged 40 to 49 years.”
Anna N. Wilkinson, MD, MSc, CCFP, of the University of Ottawa, is the corresponding author of the Journal of Clinical Oncology article.
Disclosure: Dr. Wilkinson has served as a consultant or advisor to Thrive Health. For full disclosures of the study authors, visit ascopubs.org.
