Outcomes of immediate surgery for low-risk papillary thyroid microcarcinoma in patients with or without risky features at surgery.

Active surveillance (AS) is an accepted management option for patients with low-risk papillary thyroid microcarcinoma (PTMC), although some patients undergo immediate surgery (IS). At surgery, patients may have risky features such as adhesion or invasion to the adjacent organs. The surgical outcomes of this subset of patients are unknown. Here, we investigated the surgical and oncological outcomes of these patients in comparison with others. Between 2005 and 2019, 4,635 patients were diagnosed with low-risk PTMC at our institute. Of these, 1,739 patients underwent IS. In total, 114 patients had risky features at surgery (risky feature group), while the remaining 1,625 did not (no-risky feature group). The median follow-up periods in the risky and no-risky feature groups were 8.5 and 7.6 years, respectively. The risky feature group had higher incidences of tracheal invasion (8.8%), recurrent laryngeal nerve invasion (RLN) (7.9%), and permanent vocal cord paralysis postoperatively (10.0%) and higher frequency of pathological lateral lymph node metastasis (6.1%) than the no-risky feature group (0%, 0%, and 0.2%, and 0%, respectively [p < 0.01]). However, unexpectedly, the former had a lower incidence of high Ki-67 labeling index (1.1%) and lower locoregional recurrence rate (0%) than the latter (8.3% and 0.7, respectively [p < 0.01], not calculable). None of the groups developed distant metastasis or died of the disease. The risky feature group required resection of the trachea and/or the RLN more often than the no-risky feature group. However, unexpectedly, the tumor growth activity in the risky feature group was low, and their oncological outcome was excellent.