Thyroid cancer in an iodide rich area. A histopathological study

Abstract

A comparison of the incidence of the different histological types of thyroid carcinoma in an area of high dietary iodide and an area of normal iodide intake has been made. The areas chosen were Iceland and the region of Northeast Scotland centred on Aberdeen; both areas have clearly defined populations served by a single pathology laboratory. All definite and dubious thyroid carcinomas from both regions were examined and classified by the same two pathologists. The age-specific incidence rates for papillary carcinoma in surgical specimens in both areas rose with age; they were five times higher in Iceland (high iodide area) than in Northeast Scotland. The numbers of follicular carcinomas were small, and this tumor was relatively less frequent in Iceland than Aberdeen. These findings, together with the known high relative frequency of follicular carcinoma and low frequency of papillary carcinoma in areas of endemic goitre, lead to the suggestion that the incidence of papillary carcinoma and follicular carcinoma are separately influenced by dietary iodide, papillary carcinoma being high in areas of high iodide intake and low in areas with low dietary iodide. No evidence to implicate lymphocytic thyroiditis, radiation or genetic factors in the genesis of thyroid carcinoma in Iceland or Northeast Scotland was found in this study. Undifferentiated carcinoma was about three times as common in Iceland as in Northeast Scotland. Malignant lymphoma of the thyroid was suprisingly common in Northeast Scotland, possibly related to the high frequency of thyroiditis found in this region. These studies suggest that the incidence of different histological types of thyroid malignancy is influenced by different etiological factors. They also provide support for the subdivision of thyroid malignancy into these different types, and for the general importance of accurate histological typing in cancer epidemiology.

A Study of 875 Cases of Thyroid Cancer Observed Over a Fifteen-Year Period (1975–1989) at the King Faisal Specialist Hospital and Research Centre

“…Available data indicate that following the introduction of iodine prophylaxis in other areas of the world, there had been an increase in the RF of PC over FC. [48][49][50] The same phenomenon may hold true for Saudi Arabia as well. Over the years, the population of Saudi Arabia has been variously reported to be seven million to 12.5 million.…”

Changing patterns of thyroid cancer in Sri Lanka. Has the iodination programme helped?

“…anaplastic or follicular [4]. In contrast, in countries such as Iceland where high dietary iodine is known to be associated with a low TSH level in the population, a high prevalence of papillary carcinoma is noted [15].…”

“…In Salta, the Argentina ratio increased from 1.7:1 to 3.1:1.2. The slight improvement in the last 10 years may be heralding this change that seems to be present in countries such as Scotland (3.5:1) and Iceland (6.5:1) where iodine availability is sufficient or even in excess [15].…”

Relevance of iodine intake as a reputed predisposing factor for thyroid cancer

“…Contrary to this, some of the highest incidence rates of thyroid cancer are found in Iceland (74) and Hawaii (75) (table 1), both known to have long-standing high iodine intake, although exposure to volcanic activity (where the natural radiation is higher and radiation is known to increase the development of thyroid carcinomas) has been suggested as an explanation for the high incidence in these islands.…”