Unveiling a rare BRAF mutation in minimally invasive follicular thyroid carcinoma: A case report.

[RATIONALE] Molecular testing is becoming more widely used; however, the accuracy of diagnostic testing remains a primary consideration, especially for molecular testing that detects specific mutations associated with cancers.

[PATIENT CONCERNS] A 45-year-old female without documented comorbidities presented a thyroid nodule during a routine health examination. Initial evaluation revealed a 3.8-cm nodule in the left lobe of thyroid, classified as Bethesda System category III on fine needle aspiration cytology. Genetic molecular testing detected the BRAF V600E mutation via quantitative polymerase chain reaction assay, raising concern for papillary thyroid cancer (PTC).

[DIAGNOSES] The preoperative impression was PTC based on the detection of BRAF V600E mutation.

[INTERVENTIONS] The patient underwent thyroidectomy as well as lymph node dissection with the expectation to treat PTC.

[OUTCOMES] The final pathology unexpectedly revealed minimally invasive follicular carcinoma. Confirmatory Sanger sequencing unveiled a novel sequence variation involving nucleotide duplication within the range of 1794 to 1802, a non-V600E BRAF mutation not previously reported in follicular thyroid carcinoma.

[LESSONS] This case study demonstrates the clinical relevance of exercising caution in molecular testing and its interpretation of results. For genetic testing used for diagnostic purposes, rigorous validation or cross-checking using different methods should always be considered to ensure appropriate interpretation of molecular results.