Annual Versus Biennial Screening: Diagnostic Accuracy Among Concurrent Cohorts Within the Ontario Breast Screening Program


The Ontario Breast Screening Program (OBSP) recommends annual mammography to women 50-74 at increased risk due to family history of breast or ovarian cancer or personal history of ovarian cancer or mammographic density ≥75%. Few studies have examined diagnostic accuracy of recommendations based on risk factors and included both screen-film and digital mammography (DM).


A retrospective design identified concurrent cohorts of women 50-74 screened annually or biennially with DM only between 2011 and 2014 and followed until 2016 or breast cancer diagnosis. Diagnostic accuracy measures were compared between women screened annually due to first-degree relative of breast or ovarian cancer or personal history of ovarian cancer (n = 67,795 women); mammographic density ≥75% (n = 51,956) or both (n = 3,758) and those screened biennially (n = 526,815). The association between recommendation and sensitivity and specificity was assessed using Generalized Estimating Equation models. All P values are two-sided.


For annual screening due to family or personal history versus biennial, sensitivity was statistically significantly higher (81.7% vs. 70.6%; OR = 1.86, 95%CI:1.48-2.34), particularly for invasive cancers and postmenopausal women. Although there was no statistically significant difference in sensitivity for annual screening for mammographic density ≥75%, specificity was statistically significantly lower (91.3%; OR = 0.87, 95%CI: 0.80-0.96) versus biennial (92.3%), particularly for women 50-59.


Compared to biennial screening, annual screening improved detection for women with a family or personal history of breast and/or ovarian cancer, supporting screening that is more frequent. The benefit for annual screening for women with higher mammographic density must be weighed against possible harms of increased false positives.