Cancer risk and clinicopathological characteristics of thyroid nodules harboring thyroid-stimulating hormone receptor gene mutations.

BACKGROUND: Thyroid-stimulating hormone receptor (TSHR) gene mutations play a critical role in thyroid cell proliferation and function. They are found in 20%-82% of hyperfunctioning nodules, hyperfunctioning follicular thyroid cancers (FTC), and papillary thyroid cancers (PTC). The diagnostic importance of TSHR mutation testing in fine needle aspiration (FNA) specimens remains unstudied. METHODS: To examine the association of TSHR mutations with the functional status and surgical outcomes of thyroid nodules, we evaluated 703 consecutive thyroid FNA samples with indeterminate cytology for TSHR mutations using next-generation sequencing. Testing for EZH1 mutations was performed in selected cases. The molecular diagnostic testing was done as part of standard of care treatment, and did not require informed consent. RESULTS: TSHR mutations were detected in 31 (4.4%) nodules and were located in exons 281-640, with codon 486 being the most common. Allelic frequency ranged from 3% to 45%. Of 16 cases (12 benign, 3 FTC, 1 PTC) with surgical correlation, 15 had solitary TSHR mutations and 1 PTC had comutation with BRAF V600E. Hyperthyroidism was confirmed in all 3 FTC (2 overt, 1 subclinical). Of 5 nodules with solitary TSHR mutations detected at high allelic frequency, 3 (60%) were FTC. Those at low allelic frequency (3%-22%) were benign. EZH1 mutations were detected in 2 of 4 TSHR-mutant malignant nodules and neither of 2 benign nodules. CONCLUSION: We report that TSHR mutations occur in ∼5% thyroid nodules in a large consecutive series with indeterminate cytology. TSHR mutations may be associated with an increased cancer risk when present at high allelic frequency, even when the nodule is hyperfunctioning. Benign nodules were however most strongly correlated with TSHR mutations at low allelic frequency.

Is a stable or decreasing prolactin level in a patient with prolactinoma a surrogate marker for lack of tumor growth?

The optimal interval for follow-up imaging of patients with prolactinomas is unclear. We wish to determine the likelihood of tumor enlargement in patients with prolactinomas who have a stable or reduced prolactin (PRL) level over time, whether or not they are treated with a dopamine agonist (DA). We identified 80 patients with prolactinomas (34 men, 46 women) who had at least two paired sets of serum PRL levels and pituitary MRIs, 3 or more months apart. Patients with hyperprolactinemia due to drug or stalk effects were excluded. The median (range) age was 45 (25-77) years. Sixty-three patients (78.8%) were treated with DA. PRL levels (ng/mL) at the initial and latest sets were 114 (0.3-15,732) and 16 (0.3-1,204), respectively. In patients with identifiable tumors, the maximum tumor diameters (mm) at the initial and latest MRI studies were 12.5 (2-60) and 12.5 (2-39) respectively, with an interval of 2.9 (0.3-9.7) years. Sixty percent of patients (n = 48) had a macroadenoma. Forty-two (52.5%) patients had either disappearance of the tumor (n = 22) or reduction (n = 20) in tumor size. In the remainder, tumor size was stable in 35 but increased in 3 patients. One of these patients, observed off therapy had a concomitant rise in PRL level. The other 2 had evidence of pituitary hemorrhage with no PRL increase. Tumor growth in prolactinoma patients with a stable or decreasing PRL level, regardless of size, is a rare event. Repetitive pituitary imaging in these patients may not be warranted.