Changes in thyroid cancer incidence are mainly related to better detection sensitivity of microcarcinomas

TOPIC: Incidence of thyroid cancer in France (1998-2006)

Title: Thyroid cancer: is the incidence rise abating?

Authors: Sassolas G, Hafdi-Nejjari Z, Remontet L, Bossard N, Belot A, Berger-Dutrieux N, Decaussin-Petrucci M, Bournaud C, Peix

JL, Orgiazzi J, Borson-Chazot F, and the ‘Group of Pathologists’ of the Rhône-Alpes Region.

Reference: European Journal of Endocrinology 160: 71-79, 2009

Summary

Background

Wherever it has been studied, the incidence of detected thyroid cancer is apparently rising.

Purpose

The authors used the very complete Rhône-Alpes region thyroid cancer registry, which includes all histologically proven cases since 1998, to define the incidence of thyroid cancers, their evolution, geographical distribution and subtypes. Methods &

Main Outcome measures

A total of 5.367 cases were registered during a 9-year period (1998-2006). Histological subtypes were classified according to WHO criteria (2004) by each histopathology laboratory, with the records reviewed by pathologists of reference.

Results

Mean age at diagnosis was 49 years for men and 50 years for women, with a wide age range between 10 years and more than 80 years. Sex ratio: 77% were diagnosed in women and 23% in men. The overall incidence increased from 1998 to 2001, but not thereafter. The great majority of tumors were papillary carcinomas (87%), with 44% of these presenting as classical variants and 46% as follicular variants. There were 8% of follicular carcinomas. Oncocytic, poorly differentiated, medullary and anaplastic variants represented each 1-2 % of the total. Microcarcinomas discovered incidentally, most of them of the papillary type, represented 38% of the cases. The increased incidence observed during the first four years was mainly related to an increase in the number of microcancers that were discovered fortuitously. Finally, the incidence was higher in urban (28%) than in rural conditions.

Conclusions

The increased incidence of discovered cancers reflects mostly higher detection sensitivity.

Commentary

Several studies in different parts of the world have reported an increased incidence of thyroid cancer. Although we like to mention this when writing grant proposals, the present study from France shows that the increased incidence reflects mainly a higher detection sensitivity and concerns primarily microcancers discovered fortuitously, and perhaps of minor (?) importance. The study showed that, in fact, the incidence of cancers of more than 2 cm in diameter did not increase. Therefore, there is no reason to alarm the population with the threat of a non existing new lurking danger. Let us leave scientific paranoia (as well political paranoia) to demagogues! The proportion of the various types of cancer was similar to those observed in smaller series from other Western Countries. The proportional increased incidence of urban versus rural thyroid cancer deserves to be confirmed, since it could simply be due to differences in access to specialists. As the microcarcinomas were removed, we shall never know what their evolution might have been. In future studies such as the present work, it would be of great interest to ascertain the proportion of cells in the cell cycle (Ki67 positive) and senescent (b galactosidase positive).

Summary and Commentary prepared by Jacques Dumont (Related to Chapter 18 of TDM)