Trends in thyroid carcinoma in Italy

Topic: THYROID CANCER

Title: Trend in thyroid carcinoma size, age at diagnosis, and histology in a retrospective study of 500 cases diagnosed over 20 years. Authors: Trimboli P, Graziano FM, Marzullo A, Ruggieri M, Calvanese A, Piccirilli F, Cavaliere R, Fumarola A, D-Armiento M.

Reference: Thyroid 16: 1151-1155, 2006

Summary

Background

Recently, several reports have shown that the incidence of thyroid carcinoma is increasing year after year while mortality rate is stable or even decreasing.

Purpose

To analyze the temporal trend in thyroid cancer size, age at diagnosis, and histology in a retrospective series of 500 Italian patients diagnosed aver 20 years.

Patients & Methods:

Thyroid cancer patients diagnosed between 1985 and 1994 (Group 1; n=193) and between 1995 and 2004 (Group 2; n=307).

Results:

The size of all tumors was significantly reduced from 30 – 1.4 mm in the first group to 15 – 0.8 mm in the second group. In particular, papillary thyroid carcinoma (PTC) size decreased from 28 – 1.2 mm to 14 – 0.8 mm, and follicular carcinoma from 40 – 6.3 mm to 17 – 4.5 mm. Age at diagnosis of all carcinomas increased significantly from 40 – 1.3 years in the first group to 48 – 0.9 years in the second group. Analysis of the histological types revealed a significant increase of PTC rate in the second decade from 82% to 92% and a concomitant reduction of anaplastic thyroid carcinoma (ATC) from 3.7% to 1.0%. Moreover, a significant increase of micro-PTC rate, from 7.3% to 36.4%, was observed.

Conclusions:

It is speculated that the decreased mortality rate for thyroid carcinoma reported in other series could be related to the significant reduction with time of cancer size, to the progressive increase of PTC rate and to the reduction of ATC rate. These data corroborate recent findings suggesting that age be reconsidered as an independent prognostic factor for differentiated thyroid cancers.

Commentary

Several American and European surveys have shown a trend for an increased prevalence in thyroid cancer, mainly of the papillary histotype and of micro-carcinomas. On the contrary, the mortality rate for thyroid cancer is stable or even decreases. These findings suggest that the increase is due to the widespread use of thyroid ultrasound in clinical practice with a subsequent detection of small micro-carcinomas that would have not been diagnosed in the past decades, rather than a real increase of thyroid carcinoma secondary to other factors, such as environmental or genetic background.

Comparing two different periods of thyroid cancer diagnosis, the article by Trimboli et al. confirmed that thyroid carcinomas detected in recent years were smaller, were more frequently of the papillary variant with a reduction in the more aggressive histotypes, including anaplastic thyroid carcinoma. Although thyroid cancer incidence and mortality rate were not assessed in the present study, the results are indirectly in favour of the hypothesis that thyroid cancers discovered nowadays are of so little clinical relevance that they cannot cause thyroid cancer related deaths and, thus, may account for the reduction in thyroid cancer mortality reported by the Italian Network of Cancer Registries.

An interesting, although intriguing observation of this study was that mean age at diagnosis was higher in the more recent cohort of patients. If thyroid cancer is detected more frequently at an early stage of the disease, one expects to find that the age at diagnosis would be younger rather than older. A possible interpretation of this finding may be that micro-carcinomas are tumours which remain clinically silent for many years. In view of this observation, it is also important to reconsider the prognostic impact of age on the outcome of thyroid cancer. Although age is found to be an important independent prognostic variable in several prognostic scoring systems, its importance has recently been questioned both in differentiated and medullary thyroid carcinomas. When normalizing for the life expectancy of a patient at the time of diagnosis, it is apparent that age is no longer a prognostic factor for cancer death. However, this new concept needs further validation.

( Summary and commentary prepared by Furio Pacini ) Present summary and commentary are related to Chapter N- 18 of TDM