Les tumeurs thyroïdiennes de potentiel de malignité incertain (TPMI): une entité nosologique discutée de la nouvelle classification OMS des tumeurs endocrines

Encapsulated follicular thyroid tumors can be sometimes difficult to be characterized by the pathologist, since morphological approach alone may present numerous limitations for predicting the outcome of the lesions. The inter observer variability of these encapsulated follicular lesions of the thyroid gland can be high. Diagnostic difficulties and absence of an universal consensus for identifying some encapsulated follicular lesions induce debated terminologies between some adenomas with minimally invasive follicular carcinoma or with a follicular variant of papillary thyroid carcinoma. Immunohistochemical approach and molecular analysis have been used to improve the characterization of these lesions, but these methods are rarely useful in pratice for the pathologists to define the diagnosis and the prognosis of such tumors. In this regard, an editorial from Williams et al in 2000, and the new WHO classification of endocrine tumors in 2004, suggested to label these tumors of the thyroid with “borderline”; features as, well-differentiated tumor of uncertain malignant potential (WDT-UMP), in the presence of questionable papillary carcinoma-type nuclear changes with or without questionable capsular penetration, or follicular tumor of uncertain malignant potential (FT-UMP) in the presence of questionable capsular penetration without nuclear changes. In consequence, the pathologist can write a conclusion of “tumor of uncertain malignant potential”, term which may generate great confusion among clinicians regarding the management of patients. In this review we will discussed the different elements in favor or against these terminogies.