FNA diagnosis of poorly differentiated thyroid carcinoma. A review of the recent literature

Poorly differentiated (PD) thyroid carcinomas lie both morphologically and behaviorally between well-differentiated and undifferentiated (anaplastic) carcinomas. Following the original description of this entity, different diagnostic criteria have been employed, resulting in wide discrepancies and confusion among pathologists and clinicians worldwide. To compare lesions occurring in different geographic areas and the diagnostic criteria applied in those countries, we designed a study with a panel of internationally recognized thyroid pathologists to develop consensus diagnostic criteria for PD carcinomas. Eighty-three cases were collected from Europe, Japan, and the United States, and circulated among 12 thyroid pathologists. Diagnoses were made without any knowledge of the clinical parameters, which were subsequently used for survival analysis. A consensus meeting was then held in Turin, Italy, where an agreement was reached concerning the diagnostic criteria for PD carcinoma. These include (1) presence of a solid/trabecular/insular pattern of growth, (2) absence of the conventional nuclear features of papillary carcinoma, and (3) presence of at least one of the following features: convoluted nuclei; mitotic activity >or=3 x 10 HPF; and tumor necrosis. An algorithmic approach was devised for practical use in the diagnosis of this tumor.

Poorly differentiated thyroid carcinomas (PDTC) occupy an intermediate position at the prognostic level on the spectrum of thyroid carcinoma progression. However, their histologic definition is controversial. The objective of the current study was to assess the prognostic significance of PDTC defined on the basis of mitosis and necrosis and search for prognostic markers within this group of tumors that are predictive of overall survival (OS) and progression-free survival (PFS). PDTC was defined as thyroid carcinoma with follicular cell differentiation at the histologic and/or immunohistochemical levels and displaying tumor necrosis and/or > or = 5 mitoses per 10 high-power fields (x400). Retrospective chart review and microscopic examination identified 58 patients with primary tumors meeting the above criteria and seen at the Memorial Sloan-Kettering Cancer Center between 1992 and 2004. These 58 patients were analyzed for various histologic, clinical, and imaging parameters. Each parameter was correlated with OS and PFS. Of the 58 patients studied, 22 (38%) patients died of disease with a 5-year OS rate of 60%. Forty-three of the 58 patients (74%) developed disease recurrence or disease progression, with a 5-year PFS rate of 25%. The median follow-up for the entire patient population was 42.6 months (range, 4-205 mos). A tumor size > 4 cm was found to be correlated with a decreased PFS time (P < 0.001). Those tumors with a capsule demonstrated a significantly improved OS compared with unencapsulated tumors (P = 0.001). The extent of capsular invasion was found to be a significant adverse factor for PFS (P = 0.05). The presence of extrathyroid extension into perithyroid soft tissue was found to be correlated with a decreased OS (P = 0.001) and PFS (P = 0.004). Of 27 patients with distant metastasis, 19 (70%) had concentrated radioactive iodine (RAI) at their metastatic sites. On multivariate analysis, extrathyroid extension and tumor size emerged as the only significant variables in predicting PFS (P = 0.04 and P = 0.01, respectively) whereas extrathyroid extension was found to be the sole independent prognostic factor for OS (P = 0.01). Growth pattern and cell type did not appear to influence outcome. PDTC defined on the basis of mitosis and necrosis constitutes a group of tumors that is more aggressive and homogeneous than PDTC defined by growth pattern. Within this group of patients, microstaging (tumor size, the extent of capsular invasion, and, especially, extrathyroid extension), and not growth pattern or cell type, is able to stratify patients into different prognostic categories. RAI uptake occurs in a significant number of patients with PDTC. (c) 2006 American Cancer Society.

Thyroid cancer is rare, but it is the most frequent endocrine malignancy. Its prognosis is generally favorable, especially in cases of well-differentiated thyroid cancers (DTCs), such as papillary and follicular cancers, which have survival rates of approximately 95% at 40 years. However, 15-20% of cases became radioiodine refractory (RAI-R), and until now, no other treatments have been effective. The same problems are found in cases of poorly differentiated (PDTC) and anaplastic (ATC) thyroid cancers and in at least 30% of medullary thyroid cancer (MTC) cases, which are very aggressive and not sensitive to radioiodine. Tyrosine kinase inhibitors (TKIs) represent a new approach to the treatment of advanced cases of RAI-R DTC, MTC, PDTC, and, possibly, ATC. In the past 10 years, several TKIs have been tested for the treatment of advanced, progressive, and RAI-R thyroid tumors, and some of them have been recently approved for use in clinical practice: sorafenib and lenvatinib for DTC and PDTC and vandetanib and cabozantinib for MTC. The objective of this review is to present the current status of the treatment of advanced thyroid cancer with the use of innovative targeted therapies by describing both the benefits and the limits of their use based on the experiences reported so far. A comprehensive analysis and description of the molecular basis of these therapies, as well as new therapeutic perspectives, are reported. Some practical suggestions are given for both the choice of patients to be treated and their management, with particular regard to the potential side effects.