By Donald R. Lannin, M.D. and Shiyi Wang, M.D., Ph.D.
The recent article by Welch et al.1 in the Journal showed clearly that since the adoption of widespread screening mammography, small breast cancers have increased in incidence over three times more than large cancers have decreased. This implies that many small cancers are not destined to progress to large cancers; instead, their detection results in overdiagnosis. This study characterizes groups of tumors that are likely to contain a large portion of overdiagnosed cancers and to explain the mechanism that may have led to their overdiagnosis.