This study examines the extent to which differences in sensitivity by age can be attributed to variations in breast density using a reliable, computer-assisted, continuous measure of per cent breast density.
We included women aged 40–79 years, not using hormone replacement therapy, who attended BreastScreen Victoria for first-round screening mammography in 1994 and 1995 (1002 breast cancers) and for subsequent-round screening (381 breast cancers) in 1995 and 1996. True positive cancers were invasive breast cancers diagnosed at screening and false negative cancers were cancers diagnosed within 24 months of a negative screening examination.
The effect of age (years) on the risk of having a false negative cancer (first round: odds ratio [OR] = 0.94, 95% confidence interval [CI] = 0.92–0.96; and second round: OR = 0.93, 95% CI = 0.90–0.96) was modestly attenuated when adjustment was made for mammographic density (first round: OR = 0.96, 95% CI = 0.94–0.98; and second round: OR = 0.94, 95% CI = 0.91–0.98). Adjusting for family history, symptom status, and tumour characteristics (grade, size and morphology) did not influence the estimates of the effects of age.
The study confirms that younger women have lower sensitivity but demonstrates that the lower sensitivity cannot be completely explained by variations in breast density.