Background and Aims: Non-surgical active surveillance is an option for patients with papillary thyroid microcarcinoma (PTMC). However, the long-term clinical outcomes after delayed surgery remain unclear. Therefore, this study was conducted to investigate the influence of the time interval from diagnosis to surgery on the long-term clinical outcomes of PTMC patients by comparing the clinical outcomes of PTMC patients with different intervals from initial diagnosis to surgery.  
Methods: The clinical data of PTMC patients undergoing delayed thyroid surgery from January to December 2015 were retrospectively analyzed. According to the interval from diagnosis to surgery, the patients were classified into short-interval group (<6 months), mid-interval group (6-12 months) and long-interval group (>12 months). Then, the patients were matched according to clinical variables such as age, sex, surgical scope, initial tumor diameter measured by ultrasound (US), extrathyroidal invasion, multifocal tumors, and central cervical lymph node metastasis. The dynamic risk stratifications (DRS) and patient structural relapse/disease persistence among the groups of patients were compared.
Results: A total of 426 patients were enrolled according to the inclusion and exclusion criteria. Of the patients, 331 cases were females and 95 cases were males; the average age was (48.9±10.1) years; the average tumor size of the initial US determination was (0.65±0.12) cm; 214 cases received thyroid lobectomy and the remaining cases were subjected to total thyroidectomy. There were 290 cases in short-interval group, 106 cases in mid-interval group and 30 cases in long-interval group, and the clinicopathologic features showed significant differences among the three groups, in which, the age was old, the proportions of male sex and cases receiving lateral lobectomy were high, tumor size was small and the incidence of extrathyroidal invasion was high in long-interval group (all P<0.05). Then, 147 patients were included for analysis after the clinicopathologic variables of the three groups of patients were matched with a in a 3:3:1 ratio, where there were 63 cases each in short-interval group and mid-interval group, and 21 cases in long-interval group. Of the patients after matching, 120 cases were females and 27 cases were males; the average age was (50.0±8.2) years; the average tumor size at the initial US was (0.63±0.14) cm; no significant differences were noted in clinicopathologic variables among groups (all P>0.05); the DRS classification showed no significant difference among the three groups (P=0.07). During the average (2.8±0.6) years of follow-up, there were no significant differences in the development of structural recurrent/persistent disease (P=0.34) and disease-free survival rates (P=0.25) among the three groups. The results of analysis of risk factors for structural recurrent/persistent disease in the PTMC patients showed that male sex (HR=2.43. 95% CI=1.21–4.91, P=0.013) and multifocal tumors (HR=2.45, 95% CI=1.24–4.83, P=0.010) are risk factors, and the period of delay of thyroid surgery is irrelevant to structural recurrent/persistent disease in the PTMC patients.
Conclusion: In PTMC patients, delayed surgery is not associated with increased risk of structural recurrent/persistent disease. The surgical treatment can be safely delayed in PTMC patients with under active surveillance.