Abstract
PurposePreoperative distinction of follicular thyroid carcinoma (FTC) from follicular thyroid adenoma (FTA) is a diagnostic challenge. Our aim was to investigate whether the Ki-67 proliferation index in fine needle aspiration material can contribute to the diagnosis of FTC.MethodsWe analyzed retrospectively cytological Ki-67 index determined in routine clinical setting and clinical data for 61 patients with FTC, 158 patients with FTA and 15 patients with follicular tumor of uncertain malignant potential (FT-UMP) surgically treated and diagnosed by histopathology at Karolinska University Hospital 2006-2017 (Cohort A). A previously published cohort of 109 patients with follicular tumors was re-analyzed as well (Cohort B).Results:In Cohort A, patients with FTC had a higher Ki-67 index (p < 0.001), larger tumor size (p < 0.001) and higher age at diagnosis (p = 0.036) compared to patients with FTA or FT-UMP. Hürthle cell differentiation, present in 50 FTA, 20 FTC and 8 FT-UMP, was associated with higher Ki-67 index (p = 0.009). Multivariate analysis of Cohort A identified a high Ki-67 index (odds ratio [OR]: 1.215, p < 0.001) and large tumor size (OR: 1.038, p < 0.001) as independent predictors of FTC. Results remained consistent after exclusion of Hürthle cell tumors and in pooled analysis of Cohort A + B. The area under curve of the Ki-67 index for predicting FTC was 0.722 and a cut-off for Ki-67 index at above 5% resulted in a specificity at 93% and sensitivity at 31%. Subgroup analysis of FTCs in Cohort A showed an association of higher Ki-67 index to extrathyroidal extension (p = 0.001) as well as widely invasive subtype (p = 0.019) based on the WHO 2017 classification.ConclusionsPre-operative Ki-67 index may add diagnostic information for a subset of patients with follicular thyroid tumors.
Highlights
The incidence of thyroid cancer has increased during the last three decades [1]
In this study we found that the Ki-67 index in fine needle aspiration (FNA) material has a predictive value in the diagnosis of Follicular thyroid carcinoma (FTC)
The criteria distinguishing FTC from follicular thyroid adenoma (FTA) and Follicular tumor of uncertain malignant potential (FT-UMP) are based on histopathological findings such as vascular and/or capsular invasion [2, 3]
Summary
The incidence of thyroid cancer has increased during the last three decades [1]. Follicular thyroid carcinoma (FTC)— the second most common type of thyroid carcinoma— accounts for approximately 10% of clinically manifest thyroid malignancies [1].Follicular lesions of the thyroid gland include the most common benign neoplasm—follicular thyroid adenoma (FTA) [2, 3]. The incidence of thyroid cancer has increased during the last three decades [1]. Follicular thyroid carcinoma (FTC)— the second most common type of thyroid carcinoma— accounts for approximately 10% of clinically manifest thyroid malignancies [1]. Follicular lesions of the thyroid gland include the most common benign neoplasm—follicular thyroid adenoma (FTA) [2, 3]. Follicular tumor of uncertain malignant potential (FT-UMP), previously termed atypical follicular thyroid adenoma (AFTA), is a variant of follicular thyroid tumors with “worrisome histological features” but which lack some necessary criteria to establish a diagnosis of FTC, i.e., capsular and/or vascular invasion [2, 3]. The malignant potential for FT-UMP is regarded as low and the majority of cases have a benign course [4]
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