Impact of Breast Cancer Screening on 10-Year Net Survival in Canadian Women Age 40-49 Years

Abstract

Purpose: In Canada, some provincial/territorial mammography screening programs include women age 40-49 years, whereas others do not. This study examines the impact of this dichotomy on the 10-year breast cancer (BC) net survival (NS) among women age 40-49 years and 50-59 years at diagnosis.

Methods: Using the Canadian Cancer Registry data record linked to death information, we evaluated the cohort of Canadian women age 40-49 years and 50-59 years diagnosed with BC from 2002 to 2007. We compared 10-year NS estimates in the jurisdictions with organized screening programs that included women age 40-49 years, designated as screeners (Northwest Territories, British Columbia, Alberta, Nova Scotia, and Prince Edward Island), with comparator programs that did not (Yukon, Manitoba, Saskatchewan, Ontario, Quebec, New Brunswick, and Newfoundland and Labrador).

Results: BC was the primary cause of 10-year mortality in women age 40-49 years diagnosed with BC (90.7% of deaths). Among these women, the 10-year NS for screeners (84.8%; 95% CI, 83.8 to 85.8) was 1.9 percentage points (pp) higher than that for comparators (82.9%; 95% CI, 82.3 to 83.5; P = .001). The difference in favor of screeners was significant among women age 45-49 years (2.6 pp; P = .001) but not among women age 40-44 years (0.9 pp; P = .328). Similarly, the incidence-based BC mortality rate was significantly lower in screener jurisdictions among women age 40-49 years and 45-49 years, but not for 40-44 years. Provincial/territorial NS increased significantly with higher mammography screening participation (P = .003). The BC incidence rate was virtually identical in screener and comparator jurisdictions among women age 40-49 years (P = .976) but was significantly higher for comparators among women age 50-59 years (P < .001).

Conclusion: Screening programs that included women in their 40s were associated with a significantly higher BC 10-year NS in women age 40-49 years, but not an increased rate of BC diagnosis. These results may inform screening guidelines for women age 40-49 years.

FIG 1.

Screener-to-comparator jurisdictions’ incidence-based BC mortality rate ratios, by 5-year age group at diagnosis, Canada, diagnosis years 2002-2007. Screening jurisdictions were defined as those with screening programs that included women in their 40s for annual recall during the diagnosis period. Screeners: Prince Edward Island, Nova Scotia, Alberta, British Columbia, and Northwest Territories; Comparators: Newfoundland and Labrador, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan, and Yukon Territory. The territory of Nunavut is excluded from both screeners and comparators because there were insufficient data to classify their screening status. Follow-up of cases for BC mortality is performed until the end of 2017. Adapted from Statistics Canada. BC, breast cancer.

FIG 2.

Ten-year cumulative female BC NS by jurisdictional screening status, Canada, 2002-2007 diagnosis period. Screeners (age 40-49 years): Prince Edward Island, Nova Scotia, Alberta, British Columbia, and Northwest Territories; Comparators: Newfoundland and Labrador, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan, and Yukon Territory. The territory of Nunavut is excluded because there were insufficient data to classify their screening status. The 95% CIs are denoted by vertical bars overlaid on the trend lines. Follow-up of cases is performed until the end of 2017. Adapted from Statistics Canada. BC, breast cancer; NS, net survival.

FIG 3.

Weighted linear regression of 10-year female BC NS by provincial screening rate, age 40-49 years, Canada excluding the territories, 2002-2007 diagnosis period. The provincial screening rate is the average of the 2003 and 2008 rates obtained from the Canadian Community Health Survey. Provincial importance weights were calculated on the basis of the relative incidence of BC over the 2002-2007 period and represented by the relative size of the respective provincial bubbles. P value corresponds to a two-sided test of the null hypothesis that the slope of the line is zero, with a significance level of .05. Adapted from Statistics Canada, Government of Canada Statistics Canada. BC, breast cancer; NS, net survival.

FIG A1.

Breast cancer incidence rate per 100,000 females by jurisdictional screening status and age group, Canada, 2002-2007. Screeners (age 40-49 years): Prince Edward Island, Nova Scotia, Alberta, British Columbia, and Northwest Territories; Comparators: Newfoundland and Labrador, New Brunswick, Quebec, Ontario, Manitoba, Saskatchewan, and Yukon Territory. The territory of Nunavut is excluded because there were insufficient data to classify their screening status. The 95% CIs are denoted by vertical bars overlaid on the trend lines. Adapted from Statistics Canada. Version released on August 23, 2022.