Abstract
The newly proposed nomenclature and diagnostic criteria for encapsulated follicular variant of papillary thyroid carcinoma (EFVPTC), the noninvasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP), could improve the consistency and accuracy of diagnosing this entity. Diagnosis of NIFTP requires evaluation of the complete tumor border or capsule. The presence of tumor invasion in follicular thyroid neoplasms with papillary-like nuclear features has been recently discussed by many authors. In this study, we examined the predictive value and association of follicular morphological characteristics with the tumor invasion. In addition, we analyzed the association between tumor encapsulation and molecular profile in EFVPTC/NIFTP cases. A total of 106 cases of FVPTC were included in the study. The tumors were grouped based on the presence of tumor capsule and characteristics of tumor border, as 1) completely encapsulated tumors without invasion, 2) encapsulated tumors with invasion, 3) infiltrative tumors without a capsule. Clinicopathological features, histomorphological features [nuclear criteria, minor diagnostic features, follicles oriented perpendicular to tumor border/capsule (FOPBC)] and molecular alterations in BRAF, NRAS, and KRAS genes were evaluated. FOPBC were significantly more frequently seen in encapsulated tumors with invasion (p = 0.008). The nuclear features were not associated with the presence of encapsulation and characteristics of tumor border. BRAF mutation was more frequent in infiltrative tumors, while NRAS mutation was more frequent in encapsulated tumors, but the results were not statistically significant (p = 0.917). In conclusion, FOPBC histomorphological feature may be associated with tumor invasion in EFVPTC/NIFTP. Additionally, BRAF/KRAS/NRAS mutation analysis may prevent inadequate treatment in these patients.
Highlights
Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer
follicular variant of papillary thyroid carcinoma (FVPTC) can be classified into three subtypes according to the presence of tumor capsule and invasive growth patterns: Encapsulated FVPTC (EFVPTC), nonencapsulated infiltrative FVPTC (IFVPTC), and nonencapsulated diffuse
When the tumors were grouped according to the presence of a capsule and capsular or vascular invasion, the number and percentage of patients in each group was as follows: 64 patients (60.3%) in group 1; 17 patients (16%) in group 2; and 25 patients (23.6%) in group 3
Summary
Papillary thyroid carcinoma (PTC) is the most common type of thyroid cancer. Several histological variants of PTC have been described in the literature, considering different criteria such as tumor. Submitted: 12 March 2017/Accepted: 25 April 2017 size, architecture (follicular, macrofollicular, cribriform-morular, solid, and micropapillary), cellular characteristics (tall cell, columnar, oncocytic, clear cell, and hobnail), presence of tumor capsule (encapsulated and nonencapsulated), additional tumor components, stromal features, or a combination of these criteria [4,5,6]. In 1960, follicular variant of papillary thyroid carcinoma (FVPTC) was introduced [7,8], and became widely recognized by the late 1970s [9]. One of the characteristics of FVPTC is follicular neoplasm composed of thyroid epithelial cells with nuclear features of papillary carcinoma [9]. FVPTC can be classified into three subtypes according to the presence of tumor capsule and invasive growth patterns: Encapsulated FVPTC (EFVPTC), nonencapsulated infiltrative FVPTC (IFVPTC), and nonencapsulated diffuse
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