Thyroid cancer is reported in the literature as a quite uncommon cancer site in several countries. Nevertheless, as a hormonal-related tumor, its distribution can possibly be affected by environmental agents influencing endocrine regulation. We evaluated the incidence distribution of thyroid cancer in a population cohort in which a comprehensive population-based cancer databank was available between 1988–92.
Age standardized incidence rates of thyroid cancer by gender were obtained from data provided by a Population-Based Cancer Registry created in 1988 in a developing country and displaying around 98% of cases with histological confirmation. Data adjustment by several distributions was carried out, and their fitness evaluated according to the obtained determination coefficients (R2).
Thyroid cancer incidence has been showing a marked increase in the studied population (two and half fold higher rates) since 1988, mainly among young women. Exponential distribution showed the best fitness modeling age-adjusted incidence data in the studied time interval (y= 0.076x2 −303.07x + 301.792, R2 = 0.74). Determination coefficients obtained by exponential adjustment at specific age strata among women were 0.83 at age 20–29 yr, 0.74 at age 30–39 yr., 0.66 at age 40–49 yr., 0.15 at age 50–59 yr., 0.24 at age 60–69 yr., and 0.22 at age 70–79 yr. A similar pattern was observed among men, but displaying lower determination coefficients.
The observed results indicate a marked and quite unexpected increase of the population based thyroid cancer incidence rates in the studied region. Besides observed in both gender, this rise seems to have mainly affected the young women in the nineties. Taking into account that new registry or diagnosis procedures for thyroid cancer were not introduced in the studied area during the considered time interval, exploration of possibly newly introduced environmental risk factors affecting the young birth cohorts started to be evaluated mainly exploring environmental risk factors (pesticides, solvents, hepatitis C virus, medicines, radiation, diet items, among others).
An important increase of thyroid cancer incidence in the analyzed region has been observed since 1988, mainly affecting young women (20–49 yr.). Incidence data trends suggest to be associated with environmental exposures introduced in the last decades in the studied area.