Agreement between digital breast tomosynthesis and pathologic tumour size for staging breast cancer, and comparison with standard mammography.

Abstract

Purpose: Tomosynthesis is proposed to improve breast cancer assessment and staging. We compared tomosynthesis and mammography in estimating the size of newly-diagnosed breast cancers. Methods: All pathologically-confirmed cancers detected in the STORM-2 trial (90 cancers, 85 women) were retrospectively measured on tomosynthesis by two independent readers. One reader also measured cancers on mammography. Relative mean differences (MDs) and 95% limits of agreement (LOA) with pathology were estimated for tomosynthesis and mammography within a single reader (Analysis 1) and between two readers (Analysis 2). Results: Where cancers were detected and hence measured by both tests, tomosynthesis overestimated pathologic size relative to mammography (Analysis 1: MD 5% versus 1%, Analysis 2: 7% versus 3%; P = 0.10 both analyses). There was similar, large measurement variability for both tests (LOA range: −60% to +166%). Overestimation by tomosynthesis was attributable to the subgroup with dense breasts (MDs = 12–13% versus 4% for mammography). There was low average bias for both tests in the low-density subgroup (MDs = 0–4%). LOA were larger in dense breasts for both tomosynthesis and mammography (P ≤ 0.02 all comparisons). Cancers detected only by tomosynthesis were more frequently in dense breasts (60–68%): for those tumours size was estimated with increased measurement variability (LOA ranging from −75% to +293%).