Trend in thyroid carcinoma size, age at diagnosis and histology in a retrospective study of 500 cases diagnosed over 20 years

Recently, the Italian Network of Cancer Registries analyzed 5101 cases of thyroid carcinoma showing a reduction of mortality rate of 4%/year. This prompts us to evaluate the temporal trend in tumor size, age at diagnosis and histology in a retrospective analysis of 500 thyroid cancers diagnosed over 20 years. Thyroid cancers were divided in two groups. The first included 193 cases diagnosed from 1985 to 1994 and the second 307 from 1995 to 2004. The size of all tumors was significantly reduced (p<0.01) from 30±1.4 mm in the first group to 15±0.8 mm in the second group. In particular, papillary carcinoma (PTC) size decreased from 28±1.2 mm to 14±0.8 mm (p<0.01) and follicular carcinoma (FTC) from 40±6.3mm to 17±4.5 mm (p<0.05). Age at diagnosis of all carcinomas increased significantly from 40±1.3 yrs in the first group to 48±0.9 yrs in the second group. Analysis of the histological types revealed a significant increase (p<0.01) of PTC rate in the second decade from 82% to 92% and a concomitant significant reduction (p<0.05) of anaplastic carcinoma (ATC) from 3.7% to 1.0%. Moreover, a significant increase (p<0.01) of microPTC rate, from 7.3% to 36.4%, was observed. In conclusion, the above mentioned decreased mortality rate for thyroid carcinoma 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. Furthermore, our data, if confirmed in other series, support the need to reconsider age as specific prognostic factor for thyroid cancer and underscore the importance to evaluate thyroid nodules smaller than 10 mm.