In an analysis of 33 cytology smears from 14 thyroid nodules collected through FNA samples that had indeterminate cytology, DNA analysis was obtained in 93% of samples, while RNA results were informative in 79% of cases for accurate detection of mutations, according to Lindsey Tolino, MBA, of the University of Pittsburgh Medical Center in Pennsylvania, and colleagues.
“We were pleasantly surprised that this high-complexity test … can be reliably performed in most thyroid [FNA] smears and provide the same accuracy of detecting thyroid cancer markers in thyroid nodules with indeterminate cytology,” co-author Yuri Nikiforov, MD, PhD, also of the Pittsburgh center, told MedPage Today.
The authors performed the ThyroSeq analysis on 33 routinely prepared slides, either air-dried prepared Romanowsky-type stained (Diff-Quik) or alcohol fixed Papanicolaou-stained slides. All slides were soaked in xylene for 1 to 3 days prior to isolation of DNA and RNA using a QIAcube extractor.
All analyzed slides had from 200-1,000 cells in each, while two smears that had <200 cells failed the RNA analysis. These slides were then compared to FNAs that were collected with ThyroSeqPreserve, a preservative solution.
Compared with the turnaround time of about 5-7 days with ThyroSeqPreserve, fixed cytology smears assessed with the ThyroSeq had a turnaround time of around 8-9 days because of the additional steps during preparation.
“The availability of ThyroSeq testing in fixed cytology smears will increase patient access and save expanses associated with the second office visit and repeat FNA biopsy,” Nikiforov noted. “Indeed, in those situations when a dedicated sample for molecular test was not collected during the initial biopsy procedure, and the nodule was found to have indeterminate cytology, currently, most patients have the repeat FNA biopsy performed in order to collect material for molecular testing.”
“Based on the results of this study, the treating physician can instead request that the available cytology smears are sent to ThyroSeq testing and expect informative test results in 80%-90% of cases,” he added. “At the end, more patients with thyroid nodules will avoid unneeded surgeries, which is the primary purpose of ThyroSeq testing.”
AACE attendee David Lieb, MD, of Eastern Virginia Medical School in Norfolk, called the study “very exciting,” and inquired about the age of the slides. Nikiforov replied that the oldest smear included in this study was 6 years old, and failed RNA analysis because of degraded nucleic acids. He noted that there’s still a good chance to get results from slides that are several years old, but cautioned that smears are destroyed during the analysis, and recommended scanning and saving digital images of the smears in the laboratory.
“We are continuing this study in collaboration with physicians at the University of Pennsylvania to not only provide expanded analytical validation but also demonstrate clinical validity of ThyroSeq in routine thyroid cytology smears,” Nikiforov said.