Although clinically evident thyroid carcinoma is not a frequent neoplasm (incidence 2.7 per 100,000 persons in La Plata, Argentina), occult carcinomas are present in a high proportion of the population, but there are marked differences along geographical lines. The purpose of the present study is to establish the prevalence of occult papillary thyroid carcinoma (OPC) in La Plata. Thyroid glands obtained from 100 consecutive adult necropsies were examined. The material was fixed in buffered formaldehyde at 4"C, serially sectioned at 2 mm intervals, and routinely processed. Eleven thyroid glands contained OPC, corresponding in three cases to multiple lesions. Eight carcinomas were found in 59 men (13.6%) and three in 41 women (7.3%). The ages ranged from 26 to 78 years. The neoplasms varied in size from microscopic foci to 9 mm in diameter. The prevalence rate of OPC in the present study is lower than that found in Finland, Japan, and the US, and higher than for the rest of the series recorded.
Cancer 64:547-551, 1989.
HYROID CARCINOMA IS not a common disease. Its T rate of incidence ranges in different countries from 0.5 to ten per 100,000 persons.'-4 The rate of incidence is 2.7 per 100,000 persons in La Plata, Argentina.' In most countries, papillary carcinoma is the most common histologic type, comprising approximately 40% to 70% of all c a ~e s . I -~* ~ Although clinically evident papillary thyroid carcinoma is not common compared with many other human cancers, the prevalence rate of occult papillary carcinoma (OPC) (smaller than 1.5 cm and clinically unsuspected) has been reported to be high, with marked differences along geographical lines (Table ).'*7-'3 Because similar statistics have not been compiled for Argentina, this study was undertaken to determine the prevalence of OPC in an Argentinian population.
Materials and Methods
Thyroid glands were obtained from 100 consecutive adult necropsies performed at Hospital General San Martin, La Plata, Argentina, between November 1985 and October 1986. The examined population consisted of 59 men (aged 20 to 89 years; X = 58.4 ? 13.7) and 41 women (aged 16