Follicular thyroid carcinoma

Abstract

Follicular thyroid carcinoma is being diagnosed less and less frequently despite the increasing incidence of well-differentiated thyroid carcinomas everywhere. This review will discuss the reasons underlying such an observation focusing on the evolution of the morphological and immunohistochemical diagnostic criteria of follicular thyroid tumors. It will address the differential diagnosis between follicular carcinoma and three tumor types-follicular adenoma, follicular variant of papillary carcinoma and poorly differentiated carcinoma-as well as the problems raised by the newly described categories of follicular tumors: follicular tumor of uncertain malignant potential, well-differentiated tumor of uncertain malignant potential and welldifferentiated carcinoma, not otherwise specified. Finally, the prognostic and therapeutic significance of some promising molecular biomarkers will be discussed within the frame of the aforementioned histopathological classification.

Classification of thyroid follicular cell tumors: with special reference to borderline lesions [Review]

“…Only groups 5 and 12, EnFPLs with capsular invasion, remained in the (low-risk) malignant category while the other groups without invasion were converted to [24]. In their retrospective study, there was not a single case of FT-UMP or a WDT-UMP potential, nor any case of encapsulated, noninvasive FVPTC which developed nodal metastasis and/or blood borne metastasis.…”

“…In our proposal, this criterion should be applied equally to all EnFPLs irrespective of PTC-N, and can be divided into two groups: 1) encapsulated non-invasive lesions (benign) and 2) invasive lesions (borderline or malignancy), which was first emphasized in our previous publication [20]. Both lesions, if they have PTC-N, are EnPTC (malignant) in the existing classifications such as the WHO classification, but as pointed out by many authors the former usually behaves as if it is benign [14][15][16][17][18][19][20][21][22][23][24]. They were further divided into five groups (#2, #3, #4, #5 and #12) as shown in Table 2.…”

“…They were minimally invasive type FTC with less than 4 foci of angioinvasion and non-capsulated invasive (diffuse infiltrative) common type PTC. Tumors with marked vascular invasion (more than 4 foci), high grade histology (increased mitoses and necrosis) and distant metastasis at presentation should be excluded from the borderline and WDA category, because their more aggressive nature was reported [10,12,23,24,[30][31][32][33][34]. Moderately differentiated follicular cell adenocarcinoma (MDA) included FTC with angioinvasion (more than 4) and aggressive PTC variants, such as tall cell, columnar cell, solid, loss of cellular polarity/cohesiveness (hobnail) variants and encapsulated carcinoma with high grade histology [8,9,20,[30][31][32][33][34][35].…”

“…In brief, common type PTC was divided in two groups: WDA (PTC with invasion and/or nodal metastasis) and MDA (highrisk PTC, such as tall cell, columnar cell, solid, loss of cellular polarity/cohesiveness and hobnail variants) [8,9,11,20,21,35,[46][47][48][49]. FTC type carcinoma was also divided into two groups depending on invasiveness but it was modified in this review because of recent prognostic data [23,24,[30][31][32][33][34].…”

“…Almost all of the patients eventually developed no recurrence and no cancer death after simple excision. These groups of thyroid tumors included in the borderline category in our classification are 1) papillary microcarcinoma (<1 cm) [37,38,40,41,42], 2) encapsulated cPTC [21,22] [19,24,60]. Needless to say, the borderline lesion must have no lymph node metastasis at diagnosis and, if present, low grade malignancy (WDA in our classification) should be applied to those cases because of positive lymph node metastasis.…”