Clinicopathologic Characteristics of Thyroid Nodules Positive for PTEN Mutations on Preoperative Molecular Testing

Abstract

Somatic and germline mutations of PTEN tumor suppressor gene are associated with follicular-pattern thyroid tumors and PTEN Hamartoma Tumor Syndrome (PHTS). The incidence of cancer in thyroid nodules positive for PTEN mutations on fine-needle aspiration (FNA) is not well defined. The aim of this study was to characterize diagnostic and phenotypic features of thyroid nodules with preoperatively detected PTEN mutations and their impact on management. Thyroid nodules with PTEN mutations on ThyroSeq v3 GC testing of FNA and core needle biopsy specimens from November 2017 to July 2020 were identified from the ThyroSeq Molecular Database. Demographic and clinicopathologic data were obtained through retrospective chart review. We identified 49 PTEN mutation-positive nodules from 48 patients. Patients were 57 years old on average (range 14-88) and 80% female. Cytology was predominantly indeterminate (73% atypia of undermined significance, 18% follicular neoplasm). There were 18 (29%) frameshift, 6 (10%) splice site, and 39 (62%) single nucleotide variant PTEN mutations. Fourteen (29%) nodules had two PTEN mutations, 5 (10%) had copy number alterations, and single cases had concurrent BRAF K601N, EZH1, and NRAS mutations. Surveillance was pursued for 27 (56%) and surgery for 21 (44%) patients (16 lobectomies, 5 total thyroidectomies). There were 14 follicular adenomas (FA), 4 oncocytic FA’s, 1 oncocytic hyperplastic nodule, and 1 encapsulated follicular variant papillary thyroid carcinoma (EFVPTC). The EFVPTC had two low-frequency PTEN mutations, PTEN locus loss, an NRAS mutation, and was a low-risk tumor with capsular but no angiolymphatic invasion. Four (8.3%) patients had confirmed or suspected PHTS, all with multiple nodules. Two had surgery finding no malignancies (2 FA). One PHTS patient had a prior thyroidectomy for a MET mutation-positive nodule that was follicular carcinoma. On US, the mean nodule size of patients who had surgery was larger than the surveillance group (3.2 cm vs. 2.3 cm, p=0.02) but there was no difference in TI-RADS level (p=0.54). There was no difference in mean nodule size (3.5 cm vs. 2.6 cm, p=0.35) or TI-RADS level (p=0.81) between PHTS and non-PHTS patients. Among surveillance patients, follow-up US was done at 1 year in 13/19 (68%) and 2 years in 3/6 (50%) of eligible cases. Only 1/19 (5%) underwent repeat FNA for increased nodule size. No thyroid malignancy was found with a mean of 1.75 years of follow-up (range 1.00-2.78). The EFVPTC patient had no recurrence after 1.05 years of follow-up. In summary, thyroid nodules with isolated somatic PTEN mutations are primarily benign and can be safely followed with serial imaging. Nodules with multiple PTEN mutations were only associated with malignancy when accompanied by an additional NRAS mutation. About 8% of patients with PTEN mutations may be PHTS patients who may be at greater risk for malignancy.