Malignant melanoma: how error amplification by screening creates spurious disease.

Abstract

The increased incidence of melanoma with little or no change in mortality has been attributed to the histopathological reclassification of benign disease as malignant, the consequence of diagnostic drift. An entirely new, additional explanation has now been found, and is defined as error amplification by screening. This previously unrecognized artefact is shown to be an inevitable consequence of the uneven operation of routine histopathological error in the diagnosis of borderline malignancy; thus, as the equality of diagnostic plus/minus is lost, it is no longer self-correcting, and the overdiagnosis of malignancy therefore outweighs its underdiagnosis: the error is then amplified by patient screening. The magnitude of this new artefact is a function of the reproducibility of routine histopathological diagnosis and the number of patients screened, and the evidence on this, and from studies done for other purposes, shows the error to be considerable. The artefact of error amplification by screening detracts from a possible role for ultraviolet radiation in the increase in melanoma incidence and provides an explanation of their erroneous association; in addition to melanoma, it could be a major source of misdiagnosis of other cancers associated with patient screening programmes.