Thyroid cancer has been unusually common in Iceland. Histological classification and TNM-staging has altered somewhat in the last decades. The aim of this study was to investigate the epidemiology of thyroid cancer in Iceland over half a century and identify factors affecting survival.
Information on all thyroid cancers diagnosed in Iceland from 1955 to 2004 was obtained from the Icelandic Cancer Registry. Tumours diagnosed post-mortem were excluded. The date of diagnosis, sex and age at diagnosis was registered. All histopathology material was re-evaluated to reclassify tumours and TNM-stage was determined. The effect of registered parameters on prognosis was determined both in uni- and multivariate analysis.
Out of 805 thyroid cancer cases in the study 588 were in women. The mean age was 51 years in women and 58 years in men. The oscillation of incidence was marked in the study period although it did not increase in the last decades of the study. The overall proportion of papillary carcinoma was around 80% and the proportion of T0-T2 tumours was 66%. Neither number has changed significantly in the last 40 years of the study. The overall disease specific 5 year survival was 88% and increased significantly in the study period. In a multivariate analysis patient's age, year of diagnosis, tumour type and TNM-stage were independent significant prognostic variables.
Thyroid cancer incidence in Iceland is no longer different to that in many neighbouring countries. Sex was not an independent prognostic parameter. The year of diagnosis was an independent prognostic factor which might indicate a more efficient treatment in later years.