Absence of peritumoral fibrosis or inflammatory infiltrate may be related to clinical progression of papillary thyroid microcarcinoma.

Rio Grande do Norte (RN) shows the highest relative incidence of papillary carcinomas in Brazil. To analyze histological features that might be associated with this incidence, the authors compared thyroid glands from 463 autopsies performed in RN with 427 surgical and autopsy glands previously studied in Sao Paulo (SP). The authors found 41 papillary thyroid microcarcinomas (PTMs) in 35 glands (8.1%), an incidence similar to the one reported in SP (7.8%). However, PTMs were predominantly nonencapsulated nonsclerosing at microscopy (44.0%), in contrast with SP where these types of lesion represented only 4 out of 32 PTMs (12.5%; P = .0046). The authors suggest that these nonencapsulated lesions with no sign of inflammation may represent an early stage that may evolve to clinical cancers, contributing to the high incidence of clinically differentiated thyroid carcinomas observed in RN.