Time Trends of Incidence Rates of Thyroid Cancer in Israel: What Might Explain the Sharp Increase

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Abstract
Background: Worldwide changes in the incidence, histological type, and prognosis of thyroid cancer (TC) have been observed. Regional differences in the spectrum of TC may be related to genetic factors, ionizing radiation, lifestyle, and nutritional iodine, as well as to the availability of medical services. Methods: Analysis of records of 5864 TC patients (diagnosed between 1982 and 2001), retrieved from the Israel National Cancer Registry. Results: The age-standardized incidence rate (ASR per 100,000 persons) of TC among Jewish women in 2001 was 12.45 (higher than generally reported in the world) and 3.68 among Jewish men. There was a significant increase in the ASR for TC between 1982 and 2001 in the Jewish population (by 101% among women and by 25% among men, p < 0.01 for both), mainly due to papillary carcinoma. TC incidence increased in the non-Jewish population from 2.33 to 6.02 in women (p < 0.05) and from 1.13 to 2.49 in men (p > 0.05). TC incidence was similar among immigrants from Europe and America arriving in Israel before 1990 or after 1990 for both genders. An improved 5-year survival was noted in patients diagnosed between 1992 and 1996 in comparison to patients diagnosed earlier: 1982–1986 (86% versus 78%, p < 0.01). Conclusions: A marked increase in TC incidence over the last two decades (mainly due to papillary carcinoma) has been noted in different Israeli subpopulations, being the highest in Jewish women. The increase trends were similar regardless of gender or ethnicity. The reasons for this rise in TC incidence and improvement in the survival are probably multifactorial and may relate partly to increased diagnostic vigilance and changes in clinical practice.