The Joint Annual Scientific Meetings of the Endocrine Society of Australia and the Society for Reproductive Biology 2018

Detection frequency of BRAF mutation in benign thyroid nodules (#156)

Sophie Lim 1 , Pavel Sluka 2 , Chris Gilfillan 3
  1. Faculty of Medicine, Nursing and Health Sciences, Monash University, Melbourne, VIC, Australia
  2. Monash University Eastern Health Clinical School, Melbourne, VIC, Australia
  3. Eastern Health, Melbourne, VIC, Australia

Background Papillary thyroid cancer (PTC) is the most common type of thyroid follicular epithelial-derived malignancy. It is usually slow-growing and most patients do not die of their disease, however a V600E mutation of the BRAF gene worsens its prognosis. This mutation is present in 40-60% of PTCs. Currently, thyroid nodules are deemed benign or malignant after cytopathological assessment; a benign cytological finding has high reliability for a benign histopathology and behaviour. As such, the incidence of BRAF V600E should be very low in such specimens.

Hypothesis That BRAF V600E mutation is not present in thyroid nodules classified benign by cytopathology.

Methods Fine needle aspirate (FNA) samples of thyroid nodules that were determined to be benign by cytopathology were used. Samples were snap frozen immediately after excision. Genomic DNA was extracted using the QIAamp DNA Micro Kit and quantified using ultraviolet spectroscopy. The presence of wild type or V600E mutant BRAF was detected using a commercial validated droplet digital polymerase chain reaction (ddPCR) with relevant negative and positive controls.

Results 63 patient samples were tested, of which only 26 could be analysed due to insufficient DNA yield. None of the 26 samples were positive for BRAF V600E. Thus, cytopathological assessment of these nodules aligned with the ddPCR analysis.

Discussion Data from this experiment suggests that BRAF V600E mutation is not present in thyroid nodules classified to be benign by cytopathology. We have therefore confirmed the reliability of a benign cytology in excluding BRAF positive PTC. This experiment was limited by the small number of samples that could be analysed; it would be worthwhile revising the biopsy technique, perhaps taking a FNA sample for ddPCR separate to one for cytopathology to increase the concentration of the extractions. Moreover, the sensitivity of the ddPCR in detecting BRAF V600E could be further explored.