Intraoperative pathologic examination in the era of molecular testing for differentiated thyroid cancer.

Background: Diagnostic thyroidectomy is typically indicated for indeterminate thyroid cytology results. Traditionally, intraoperative pathologic examination (IOPE) helped to guide the extent of initial surgery. Preoperative molecular testing (MT) of fine needle aspiration cytology has emerged as another diagnostic adjunct, is highly specific for thyroid cancer, and can lead to appropriate initial total thyroidectomy. We hypothesized that preoperative MT obviates the need for routine IOPE during lobectomy.

Study Design: In a retrospective, consecutive cohort study, we compared outcomes of 670 patients undergoing thyroidectomy. Cohort A (January 2005 to December 2006) received surgery without MT, and cohort B (January 2008 to September 2010) had preoperative MT for BRAF, RAS, RET/PTC, and PAX8/PPARγ mutations, and cytology assessment by the 2007 modified Bethesda criteria. In both cohorts, IOPE was performed during lobectomy and a positive result prompted total thyroidectomy.

Results: In cohort B, total thyroidectomy was more often the initial surgery (62% vs A 45%; p < 0.001) and a positive MT result was the only factor prompting initial total thyroidectomy in 18 (9%) patients. Among 315 patients who had initial lobectomy, thyroid cancer was infrequently diagnosed by IOPE in both cohorts (A 3.6% vs B 1.7%; p = 0.5). The sensitivity of IOPE in detecting differentiated thyroid cancer ≥1 cm decreased >60% with routine use of MT and the Bethesda criteria (A 18.4% vs B 5.9%). After lobectomy, differentiated thyroid cancer ≥1 cm was equally likely to be diagnosed in both cohorts (p = 0.1), but follicular variant papillary thyroid cancer was more common in cohort B (74% vs 45%; p = 0.02).

Conclusions: Together with the Bethesda cytologic criteria, preoperative MT allows for an increased rate of initial definitive total thyroidectomy and eliminates the need for routine intraoperative pathologic examination during diagnostic lobectomy.