Over diagnosis of thyroid cancer in the Marne and Ardennes departments of France from 1975 to 2014

Abstract

Incidence of thyroid cancer has increased considerably in France in recent years, but the mortality rate has declined only slightly. Part of this increased incidence could be attributable to over diagnosis. We aimed to estimate the contribution of over diagnosis to the incidence of papillary thyroid cancer. Incidence rates were calculated based on data from the specialised Marnes-Ardennes thyroid cancer registry, for cancers diagnosed between 1975 and 2014, by age category and by five-year period. The population was divided into two groups according to pTNM classification at diagnosis (i.e. localised or invasive). Over diagnosis was defined as the difference in incidence rates between the invasive cancer and localised cancer groups. This rate was then divided by the incidence rate in the localised cancer group for the most recent period (2010–2014) to obtain the proportion of cancers attributable to over diagnosis. In total, 2008 patients were included. The proportion of incidence attributable to over diagnosis for the period 2010–2014 was estimated at 7% and 62% in men and women aged < 50 years respectively, and at 65% and 73% respectively in men and women aged ≥ 50 years. We observed a high proportion of cancers attributable to over diagnosis. This finding raises the issue of patient management, with the risk of over treatment, and the repercussions on quality of life for patients diagnosed with cancer.