Thyroid cancer in South Africa - an indicator of regional iodine deficiency

Objective. Because follicular thyroid cancers predominate in iodine-deficient and papillary cancers predominate in iodine replete populations. we have analysed national and regional (former Transvaal) incidences of these cancer types as a surrogate measure of the population iodine nutritional status in South Africa.Design. Statistical analysis, by race and sex, of differentiated thyroid cancers reported to the South African National Cancer Registry (1988), and of the computerised histology records of the Department of Anatomical Pathology, SAIMR (January 1990 to June 1994; Transvaal data).Main outcome measures. Relative frequencies of the two cancer types nationally and geographically in the Transvaal region.Main results. Thyroid cancer was underdiagnosed in populations other than white. Nationally, follicular histology accounted for 55% of all differentiated primary thyroid cancers, and predominated especially in black women. Follicular morphology predominated in blacks resident in the rural regions of the former Transvaal (58%), while papillary histology predominated in urban areas (of present-day Gauteng), irrespective of race (78%; P = 0.003).Conclusion. The national predominance of follicular thyroid cancer indicates that significant iodine deficiency exists in the country as a whole. The observed urban-rural differences in prevalences of follicular and papillary cancer types suggest regional differences in the severity of iodine deficiency. There is a need for a formal survey of the population iodine nutritional status in South Africa