SAN DIEGO – Routine preoperative use of genetic testing to detect mutations implicated in thyroid carcinogenesis can help guide perioperative decision making, though risks associated with mutations are not always clear-cut.
For individuals with thyroid cancer (TC), the presence of certain mutations was associated with higher risk of early recurrence of cancer as well as distant metastases, according to a recent study presented by Dr. Linwah Yip at the annual meeting of the American Surgical Association. She and her colleagues at the University of Pittsburgh built on their previous work to characterize how thyroid cancer genotype relates both to cancer histology and to disease-related outcomes.
Using data from the electronic medical record of a single institution, Dr. Yip and her colleagues examined data from consecutive patients who had initial surgery for histologically confirmed TC. Of the 1,510 patients in the study cohort, 77% were women, and patients had a mean age of 49 years. All of the cancers in the study were tested for mutations in seven genes known to be associated with thyroid carcinogenesis. Mutation testing was a routine part of preoperative care for thyroid cancer patients, often performed on preoperative fine needle aspiration (FNA) biopsy.
Outcomes tracked in the study, Dr. Yip said, included the type and stage of thyroid cancer identified and whether the cancer recurred.
Mutations were found in 1,039 patients (69%), and no more than one mutation was found in any one tumor. No tumor genotype was specifically associated with tumor size or whether the tumor was multifocal.
Overall, BRAF V600E was the most common mutation associated with TC, and patients with this mutation were the ones most likely to have a recurrence (P = .001). However, Dr. Yip noted that there is phenotypic heterogeneity in how the recurrences present. More distant metastatic disease and lateral lymph node metastases were most likely with RET/PTC1 and three mutations (P = .02).
By contrast, about 25% of thyroid cancers in the study showed mutations in RAS, PAX8/PPARG, or BRAF K601E. These mutations were associated with a more indolent disease course, with more encapsulated tumors and an overall disease-free survival of nearly 100% at 5 years after diagnosis. Dr. Yip said, “However, RAS variations can be associated with any histologic type of thyroid cancer, including anaplastic.”
Dr. Yip said that clinicians should consider conducting perioperative neck ultrasound with lymph node mapping if BRAF V600E or RET/PTC mutations are found. Her recommendation for these patients was a total thyroidectomy, with consideration of a central compartment neck dissection performed prophylactically, in light of the > 50% chance for lymph node involvement. Additionally, surveillance for distant metastases in the form of a chest CT should be considered when tumors are REC/PTC positive.
Study limitations include its retrospective nature and the fact that the treating physicians were not blinded to mutation testing results. Additionally, Dr. Yip noted, in patients with multifocal disease, only the most aggressive tumor was included.
Dr. Chris McHenry of Case Western Reserve University, Cleveland, noted in discussion that disease-specific survival was not related to mutation testing in this study. For patients with advanced thyroid cancer who have limited treatment options, however, mutation testing may help direct specific adjuvant therapies based on risk.
Dr. Nikiforov is a consultant for Quest Diagnostics. The others reported no disclosures.
The complete manuscript of this study and its presentation at the American Surgical Association’s 135th Annual Meeting, April 2015, in San Diego, California, are anticipated to be published in the Annals of Surgery pending editorial review.