The utility of combined mutation analysis and microRNA classification in reclassifying cancer risk of cytologically indeterminate thyroid nodules

Abstract

ObjectivesReal‐world clinical results of (1) Bethesda categorization, (2) mutation analysis, and (3) a microRNA classifier were correlated to show the utility of molecular analysis in assessing malignancy risk of indeterminate thyroid nodules.MethodsCytology and molecular results of clinically tested thyroid nodules were compared. An additional microRNA threshold was determined based on nodules with known disease status, establishing a 3‐tiered microRNA approach to clinical risk assessments. Expected rate of malignancy given mutation panel and 3‐tiered microRNA approach was validated in an independent cohort of atypia of undetermined significance or follicular lesion of undetermined significance (AUS/FLUS) and follicular neoplasm or suspicious for follicular neoplasm (FN/SFN) nodules with surgically derived outcomes.ResultsIn 2685 patients clinically tested, PIK3CA, PAX8/PPARγ, and RET/PTC mutations occurred in less than 1%. Of note, 2% had BRAFV600E mutation and 82% lacked mutations. The maximum expected risk of malignancy in nodules lacking mutations was 9% and 17% for AUS/FLUS and FN/SFN nodules, respectively. Positive microRNA status further increased risk, with the most worrisome status (level‐3) elevating risk to 36% and 54%, respectively. RAS mutations occurred in 15% of nodules tested clinically, including in 8% of those that were cytologically benign. The maximum expected risk of malignancy in nodules with RAS or PAX8/PPARγ mutations was 49% and 65% for AUS/FLUS and FN/SFN nodules, respectively. Positive microRNA status further increased risk, with the most worrisome microRNA status (level‐3) elevating risk to 85% and 91%, respectively.ConclusionsMutation panels alone do not sufficiently risk stratify thyroid nodular disease. microRNA classification complements cytology and mutation analysis with the capacity to better differentiate nodules at high risk of malignancy.

Clinical impact of testing for mutations and microRNAs in thyroid nodules

“…An MPT positive result placed patients at 13 times higher risk of malignancy compared to those with an MPT negative result, which carried a high probability (92%) of cancer-free survival over 2 years follow-up. These risk classifications are consistent with those reported by others who have shown that micro-RNA analysis can help reclassify cancer risk of nodules with weak driver mutations 16. We show that incorporation of microRNA testing of nodules with weak driver mutations into MPT significantly improved the rate of a negative MPT test result from 69% to 87% in our study cohort at 14% cancer prevalence.…”

“…6 While mutations strongly associated with malignancy, such as BRAF V600E, RET fusions, and TERT can assist in surgical decision making, other mutations considered weak drivers of cancer carry less certainty. 16,17 Multiple studies have described the ability of RNA-based risk classifiers to help resolve diagnostic uncertainty in indeterminate thyroid nodules. [11][12][13][14][15] Furthermore, residual risk of malignancy (5%-25%) is present in patients who lack any detectable mutational change.…”

“…19,20 However, its less than optimal positive predictive value limits the ability to rule in the need for surgery, especially in AUS/FLUS nodules, where malignancy rates are low. 16 However, there has previously been limited data supporting the impact of MPT results on real-world decisions to surgically treat nodules or on the outcomes of patients who have undergone such testing in clinical practice. 18 Given the improved performance of the combination approach, this multiplatform combination of mutations and microRNA test (MPT) can effectively help to rule in and rule out the need for surgery.…”

Incremental utility of expanded mutation panel when used in combination with microRNA classification in indeterminate thyroid nodules

“…5 Without additional testing, diagnostic lobectomy is often required for definitive diagnosis, concluding most frequently in benign disease in the form of nodular hyperplasia, follicular adenoma, or related noncancerous processes for which tissue resection may have been unnecessary. [7][8][9] However, inclusion of additional mutations and fusions that is not highly specific for malignancy may result in panels with lower positive predictive value (PPV). 6 When faced with an indeterminate cytology diagnosis, molecular testing is often used in routine clinical practice to further assess the risk of malignancy.…”

“…8,[22][23][24][25] Other mutations and fusions can occur at a much lower frequency, making their PPV difficult to study and consequently not well understood. RAS mutations are the most common to indeterminate nodules and have been found in both benign and malignant nodules, presenting an uncertain PPV ranging from 15% to 70%.…”