The increase in thyroid cancer incidence is not only due to papillary microcarcinomas: a 40-year study in 1 778 patients

Aim: Thyroid cancer incidence has been increased over the last decades. The aims of the present study were: (a) to identify a changing trend in thyroid cancer in Northern Greece, (b) to examine patients' and tumoral characteristics and (c) to investigate the increase of papillary microcarcinomas and that of invasive or larger cancers.

Patients and methods: We retrospectively analyzed the records of 1 778 patients who were diagnosed with thyroid cancer between January 1971 and December 2010. The study period was divided into 4 decades: 1971-1980, 1981-1990, 1991-2000, 2001-2010. Patients were separated into 2 groups: in Group A we have included papillary thyroid microcarcinomas (PTM) and in Group B all cancers with diameter >10 mm as well as invasive cancers ≤10 mm.

Results: Patients diagnosed with thyroid cancer increased substantially per decade. The relative frequency of papillary thyroid cancer cases increased (from 60% up to 84.6% in the last decade) and follicular cancers decreased (from 40% down to 11.6%). During the study period, cancer size declined. Frequency of PTM (Group A) increased from 0% up to 19.3% in the last decade, but cancers of this group represent only a minority of total cancers.

Conclusions: The increase of thyroid cancer in this cohort was mainly due to tumors larger than 1 cm and also to smaller in size but invasive thyroid tumors. This increase outnumbers the increase in papillary thyroid microcarcinomas.