Clinical and Pathologic Characteristics of Cytologically Indeterminate Thyroid Nodules with Non-V600E BRAF...

Molecular assays serve as a potential risk stratification tool for cytologically indeterminate thyroid nodules (ITNs). BRAF V600E mutations are nearly always associated with thyroid cancer. However, the malignancy risk for ITNs with other less common BRAF alterations is less well understood. In this retrospective cohort study, we examine the risk of malignancy (ROM), histopathologic diagnoses, and clinical outcomes for non-V600E BRAF-altered ITNs.

Genomic profiling data obtained from 1034 pre-operative fine-needle aspiration samples from 955 patients were reviewed. Nodules harboring BRAF V600E were excluded. Clinical, radiographic, and histopathologic data were analyzed retrospectively from BRAF-altered ITNs managed surgically at one comprehensive cancer center (2014-2024). Diagnoses were subdivided based on American Thyroid Association (ATA) risk categories.

Thirty-seven patients (3.9%) with non-V600E BRAF-altered ITNs were identified (isolated BRAF mutation: n = 29 [78.4%], BRAF + other mutation: n = 3 [8.1%], BRAF fusion: n = 4 [10.8%], BRAF-like gene expression: n = 1 [2.7%]). All BRAF mutations identified in the cohort were class II (RAS-independent, intermediate to high kinase activity). Nodules had a median pre-operative diameter of 1.8 cm (interquartile range [IQR] 1.4-2.5). Patients presented with nodal metastases in 2.7% (n = 1) of cases, and local invasion was not identified in any patients in the cohort. Approximately half of patients (54.1%) were initially treated with a partial thyroidectomy (lobectomy: n = 17 [45.9%], isthmusectomy: n = 3 [8.1%]), and the remaining patients underwent total thyroidectomy (n = 17 [45.9%]). Median post-operative follow-up was 28 months (IQR 17.8-45.5). ROM for BRAF alterations was 73% (95%CI 59-87%; ATA low risk: 64.9%/ATA int risk: 5.4%/ATA high risk: 2.7%). There were no high-risk cancers identified in patients with isolated BRAF mutation (benign: n = 10 [34.5%], ATA low risk: n = 19 [65.5%]), and the most common isolated mutation was K601E (n = 17, 45.9%) which had a 58.8% ROM (all ATA low risk). Patients with isolated BRAF mutations had a significantly lower rate of ATA intermediate or high risk pathology when compared to all other BRAF alterations (0% vs. 37.5%, p = 0.0072). Only three patients were treated with radioactive iodine post-operatively (8.1%), and no completion thyroidectomy procedures were performed in those who did not initially undergo total thyroidectomy. No patients in the cohort were found to have distant metastatic disease or recurrence, and there were no deaths during the follow-up interval.

ITNs harboring non-V600E BRAF alterations were rare (3.9% of patients) and typically malignant (73%). Nearly all nodules were benign or ATA low-risk cancers. Only 8% of such nodules were ATA intermediate or high risk cancers. In ITNs with isolated non-V600E BRAF and no other genetic alterations, one-third were non-malignant, and all cancers were ATA low risk. In the appropriate clinical context, thyroid lobectomy or active surveillance can be considered for initial management of non-V600E BRAF-altered ITNs.