Overdiagnosis means receiving a diagnosis that is not likely to benefit you. Early detection of disease conditions can be a double-edged sword. For some people, it prevent serious illness, for others there is the tendency to overdiagnose and overtreat things that would never progress and never cause any harm.
The most widely accepted definition of ''overdiagnosis'' is ''diagnosing a person without symptoms with a disease that will (ultimately) never cause symptoms or death during the person's lifetime''. It should not be confused with misdiagnosis or false-positive findings. The real issue lies with ''overtreatment'' of these accurate diagnoses rather than overdiagnosis itself.
A 2015 study published in the New England Journal of Medicine stated that 14.5 million Americans with a history of cancer were alive on 1 January 2014 but it did not qualify the statement by acknowledging the great burden of cancer diagnoses that are now known to be intrinsically benign, e.g. ductal carcinoma in situ (DCIS) "breast cancers" and high-grade intraepithelial prostatic neoplasia (HGPIN) "prostate cancer". A 2012 National Cancer Institute commissioned expert working group recommended that these "cancers" were misclassified and should be reclassified as benign lesions of epithelial origin, presumably better left untreated. This reclassification of certain 'cancers' to benign growths also encompasses so-called papillary carcinomas of the thyroid, a fundamentally harmless nodular growth the conventional medical establishment still calls thyroid cancer and treats aggressively.