Analysis of <i>PLEKHS1</i> promoter mutation in preoperative thyroid nodule samples

Indeterminate thyroid nodules carry a wide range of malignancy prevalence, necessitating incorporation of molecular testing to guide management. Molecular test results help guide prognosis to a certain extent, but additional prognostic factors need to be identified. Limited data have linked PLEKHS1 promoter (PLEKHS1p) mutations with higher aggressiveness of thyroid cancer. Hence, we aimed to evaluate the diagnostic and prognostic value of PLEKHS1p mutations in preoperative thyroid nodules undergoing molecular testing. We assessed PLEKHS1p mutations in 9279 patient samples from April 2023 to June 2024 among indeterminate thyroid nodules ((B)ethesda III/IV) with Afirma GSC-(S)uspicious results as well as among B V/VI cytology thyroid nodules. We also analyzed a subset of 20 consecutive cases positive for PLEKHS1p mutations with surgical resection for histology and for co-occurring molecular alterations from the Afirma testing. PLEKHS1p mutations were positive in 60/9279 (0.6%) of patient samples with three times higher frequency in B VI compared to B III cytology nodules (1.36% vs 0.47%, p < .01). Among the 60 samples harboring PLEKHS1p mutations, 28 had the C593T hotspot mutation, 38 the G590A mutation, and six samples had both; four samples had concomitant TERTp mutations and 18 samples had concomitant BRAFp.V600E alterations. Our study demonstrated an overall low frequency of PLEKHS1p mutations, but this frequency was highest among malignant (B VI) cytology thyroid nodules. The frequency of PLEKHS1p mutations did not strongly correlate with the severity of thyroid cancer but the surgical sample size was limited. Further research is needed to clarify the role of PLEKHS1p mutations in thyroid nodules and cancer.