Recent trends in the incidence, geographical distribution, and survival from thyroid cancer in Wales, 1985-2010.

BACKGROUND

Previous studies of thyroid cancer incidence in Wales have given varying results with suggestions of an excess of cases in geographic areas that were previously exposed to the radioactive fallout from the 1986 Chernobyl nuclear reactor incident. Our objective in this study was to provide an up-to-date comprehensive analysis of time trends in the incidence, geographical distribution, and survival from thyroid cancer in Wales.

METHODS

We identified thyroid cancer cases, registered from 1985 through 2010 in the Welsh Cancer Intelligence and Surveillance Unit (WCISU). Age standardized rates were determined from the European standard population. A Poisson regression model was fitted to assess temporal trends and rate ratios (RRs) and confidence intervals (CIs) were determined and compared across consecutive time periods: 1985-1997 and 1998-2010. Standardized incidence ratios were calculated for each of the 22 local authority areas. Relative survival and Kaplan-Meier curves were computed to analyze all cause and thyroid cancer-specific survival.

RESULTS

A total of 1747 thyroid cancer cases were registered from 1985 to 2010. Age standardized incidence rates were 2.8 and 1.2 per 100,000 population per year for females and males respectively. Incidence rates increased with time (RR 1.3 [CI 1.2-1.5], p < 0.001; 1998-2010 vs. 1985-1997). The incidence of papillary cancer increased progressively over the study period (RR 2.22 [CI 1.91-2.57], p < 0.001; 1998-2010 vs. 1985-1997), while rates for other (nonpapillary) histological subtypes remained static (RR 0.95 [CI 0.84-1.08], p = 0.45; 1998-2010 vs. 1985-1997). We identified two geographical areas of increased incidence, but the spatial distribution of cases was inconsistent with exposure to radioactive fallout. Five-year relative survival from all-cause mortality improved from 74.2 [CI 66.8-80.1] in 1985-1989 to 82.6 [CI 77.1-86.9] in 2000-2004, but remained poor for patients over the age of 65 years (p < 0.001, > 65 years vs. 15-64 years) and patients with anaplastic thyroid cancer (p < 0.001; anaplastic vs. other histological varieties).

CONCLUSIONS

The incidence of thyroid cancer has increased in Wales, predominantly due to an increase in papillary cancers. The current geographical distribution of cases does not support a radiation effect in the region. Survival has remained poor for patients over the age of 65 years and those with anaplastic carcinoma.