The Evaluation of Prognostic Factors in Differentiated Thyroid Cancer

Abstract

Thyroid cancer is rare among human malignancies, account for approximately 1-2% of all malignancies, but it is the most frequent endocrine cancer. A new pathological classification was introduced in 2017 by the World Health Organization (WHO) (Table 1). Papillary (PTC) and follicular (FTC) thyroid cancers, also known as differentiated thyroid carcinomas (DTC), belong to the primary thyroid tumors and derive from the thyroid follicular epithelial cells. The word ’differentiated’ refers to that the cancer cells look and act in some respects like normal thyroid cells. PTC and FTC account for more than 90% of all thyroid cancers. The DTC have a relatively good prognosis with proper treatment, the 10-year survival is above 90%, however, there are several cases in which rapid progression and poor outcome can be perceived. There is an urgent requirement to better understand biological behavior of thyroid cancers, and to find reliable prognostic factors. In the 2017 WHO classification, the borderline thyroid tumors have been distinguished for the first time {follicular tumor of uncertain malignant potential (FT-UMP), well differentiated tumor of uncertain malignant potential (WDT-UMP), noninvasive follicular thyroid neoplasm with papillary nuclear features (NIFTP)}. Borderline tumors are equivalent to carcinoma in situ in other organs. They are placed between follicular adenoma, follicular carcinoma or follicular variant of PTC. In the new classification 15 variants of PTC are described. Many of them have worse prognosis than the classical variant. The exact prognostic significance of the rare variants is not well-characterized. The Hobnail variant was introduced as a new entity. FTC are grouped being minimally invasive, angioinvasive and widely invasive. Hürthle-cell tumors are categorized as a separate entity. This category includes Hürthle-cell adenoma and Hürthle-cell carcinoma which were previously classified as oncocytic variants.