POORLY DIFFERENTIATED FORMS OF PAPILLARY THYROID-CARCINOMA - DISTINCTIVE ENTITIES OR MORPHOLOGICAL PATTERNS

The concept that poorly differentiated carcinomas (PDC) represent a gr oup in an intermediate position in the spectrum of follicular cell-der ived carcinomas of the thyroid gland is currently well established. Be cause at the well-differentiated end of the spectrum there are two gro ups of entities with distinct biological characteristics, ie, the papi llary carcinoma (PC) and the follicular carcinoma (FC), we examined th e group represented by PCs to ascertain whether papillary carcinoma-re lated PDCs (pPDC) represent merely a histologic variant or a distinct pathologic entity. For this purpose 227 consecutive PCs were reclassif ied according to current criteria. The association between the presenc e of a tumoral pattern consistent with pPDC (response variable), and p rognostic factors such as gender age, pTNM (predictive variables) was evaluated in terms of odds ratio statistics. One hundred eighty-three of 227 cases, defined as PCs met the World Health Organization criteri a of the not otherwise specified (NOS) (79 cases), microcarcinoma (65 cases), encapsulated (4 cases) and follicular (35 cases) variants. For ty-four cases, defined as pPDCs, met those of the tall cell (39 cases) , columnar cell PC (2 cases) and mixed tall cell-columnar cell PC (3 c ases) variants, Statistical analyses of the two groups of patients sho wed a significant correlation between differentiation and age above 40 years, extrathyroid tumor extension and low ratio of regional nodal i nvolvement at the onset of disease. More strikingly they also showed t hat morphology, ie, a tumoral pattern consistent with pPDC (differenti ation), is the strongest predictor of biological behavior including re currences and recurrence-related deaths that appear to occur five and twenty times more frequently in pPDCs than in PCs, respectively. On th e basis of these findings, we conclude that pPDCs represent a distinct high-risk clinicopathologic entity among PCs. Copyright (C) 1995 by W .B. Saunders Company