Abstract
IntroductionMammographic density (MD) is the strongest risk factor for breast cancer. It is also strongly associated with interval cancers (ICs) due to decreased screening sensitivity and possibly by also giving rise to more aggressive tumors. With this information as background, we compared survival in interval and screen-detected cancers, taking MD into consideration.MethodsThe patients were postmenopausal women ages 50 to 74 years who were diagnosed with breast cancer in Sweden between 1993 and 1995. A total of 1,115 women with screen-detected cancers and 285 with ICs had available mammograms. Cox proportional hazards models were used to compare breast cancer-specific survival between interval and screen-detected cancers stratified on MD.ResultsHazard rates for breast cancer-specific survival were approximately three times higher in ICs than in screen-detected cancers, independent of MD. After adjustment for tumor size, a proxy for time to diagnosis, ICs in nondense breasts still had a statistically significantly increased hazard rate compared to screen-detected cancers in nondense breasts (5-yr survival hazard ratio (HR) 2.43, P = 0.001). In dense breasts, however, there was no longer evidence of a difference in survival between ICs and screen-detected cancers (5-yr survival HR 1.41, P = 0.486).ConclusionsIn nondense breasts, ICs seem to be truly more aggressive than screen-detected cancers. In dense breasts, the poorer prognosis of ICs compared to that of screen-detected cancers may be attributable at least partially to later detection. However, to the best of our knowledge, this study is the first to investigate these relationships, and further studies are warranted to confirm our results.
Highlights
Mammographic density (MD) is the strongest risk factor for breast cancer
interval cancer (IC) are usually separated into “true” ICs, that is, cancers that could not be detected on the previous mammogram and cancers missed at a previous mammography, that is, false-negative examinations
There is some evidence that MD is associated with more aggressive tumor characteristics [11,12,13], but most studies have found no association between MD and tumor characteristics [14,15,16,17,18,19]
Summary
Mammographic density (MD) is the strongest risk factor for breast cancer It is strongly associated with interval cancers (ICs) due to decreased screening sensitivity and possibly by giving rise to more aggressive tumors. ICs are usually separated into “true” ICs, that is, cancers that could not be detected on the previous mammogram (and truly have arisen within the screening interval) and cancers missed at a previous mammography, that is, false-negative examinations. The former are thought to be more aggressive and have a poorer prognosis than screen-detected (SD) cancers [2]. There is some evidence that MD is associated with more aggressive tumor characteristics [11,12,13], but most studies have found no association between MD and tumor characteristics [14,15,16,17,18,19]
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