Patient characteristics
This study included 60 patients (18 males and 42 females) and the corresponding flow chart were displayed in Figure 1. The mean age was 44.1±13.8 years (interquartile range, IQR, 33–54 years) and age ≥ 45 and ≥ 55 were seen in 29 (48.3%) and 14 (23.3%) patients, respectively. Forty-nine (81.7%) patients underwent RAI therapy. The characteristics of the patients were presented in Table 1. The mean size of the tumor was 21.7±14.3mm and tumor diameter > 40mm were found in 7 (11.7%) patients. Multifocality and bilaterality were identified in 11 (18.3%) and 8 (13.3%) patients, respectively. T3 stage were found in 16 (26.7%) patients while T4 in 19 (31.7%) patients. The mean numbers of total harvested and involved LNs were 33.0±20.8 and 8.5±8.2, respectively.
Follow-up
During the median follow-up of 29 months (range, 13-78months), 8 (13.3%) patients maintained TgAb-positive (TgAb > 115U/mL). Central, lateral and both compartments LN recurrence were noted in 19 (31.7%), 36 (60.0%) and 5 (8.3%) patients, respectively. The mean diameter of the largest recurrent LN was 18.7±12.9mm. Extranodal extensions were observed in 20 (33.3%) patients. At the end of follow-up, all patients stayed alive.
Maximum uTg levels ≥ 0.2 ng/mL were detected in 42 (70%) patients and maximum uTg levels < 0.2 ng/mL were found in 18 (30%) patients during follow-up. In 49 patients who underwent RAI treatment, 34 (69.4%) were with an off-Tg ≥ 1 ng/mL and 15 (30.6%) were with an off-Tg < 1 ng/mL, while 31 (63.3%) were with an on-Tg ≥ 0.2 ng/mL and 18 (36.7%) were with an on-Tg < 0.2 ng/mL.
Meanwhile, in 52 patients with TgAb-negative (< 115U/mL), 39 (75.0%) and 13 (25.0%) patients were appeared with maximum uTg levels ≥ 0.2 ng/mL and < 0.2 ng/mL respectively (Table 2). Forty-three patients received RAI and 33 (76.7%) of them were with an off-Tg ≥ 1 ng/mL, and 10 (23.3%) of them were with an off-Tg < 1 ng/mL (Table 3), while 30 (69.8%) were with an on-Tg ≥ 0.2 ng/mL and 13 (30.2%) were with an on-Tg < 0.2 ng/mL (Table 4).
Univariate analyses of factors associated with positive Tg levels
The maximum uTg ≥ 0.2 ng/mL were significantly associated with older age, higher possibility of diameters of recurrent LNs ≥ 25mm and higher LNs metastatic rate (P = 0.024, 0.045 and 0.039, respectively). In 49 patients underwent RAI treatment, off-Tg ≥ 1ng/mL were significantly associated with older age, larger diameter of recurrent LNs and higher possibility of diameters of recurrent LNs ≥ 25mm (P = 0.042, 0.021 and 0.038, respectively). Older age, larger diameter of recurrent LNs and higher possibility of diameters of recurrent LNs ≥ 25mm were also seen in patients with on-Tg ≥ 0.2 ng/ml (P = 0.017, 0.020 and 0.008, respectively). However, lower rate of multifocality of the primary tumor was found in patients with off-Tg ≥ 1ng/mL and on-Tg ≥ 0.2 ng/ml (P = 0.047 and 0.039, respectively).
When excluding the interference of TgAb-positive (Table 2), the maximum uTg levels ≥ 0.2 ng/ml were significantly associated with larger diameter of recurrent LNs (P = 0.027), higher possibility of diameters of recurrent LNs ≥ 25mm (P = 0.023) and higher LN metastatic rate (P < 0.001). In the 43 patients with TgAb-negative who underwent RAI treatment, off-Tg ≥ 1ng/mL (Table 3)was significantly associated with larger diameter of recurrent LNs (P = 0.018) and higher possibility of diameters of recurrent LNs ≥ 25mm (P = 0.047). Larger diameter of recurrent LNs (P=0.020), higher possibility of diameters of recurrent LNs ≥ 25mm (P = 0.013), and lower rate of multifocality (P=0.032) were also seen in patients (Table 4) with on-Tg ≥ 0.2 ng/mL.
Independent predictors of positive Tg levels
In multivariate analysis, the number of metastatic LNs ≥ 8 was an independent predictor for maximum uTg ≥ 0.2 ng/mL in patients with TgAb-negative (OR = 8.767; 95% CI = 1.392-55.216; P = 0.021), while multifocality was an independent protective factor for maximum uTg ≥ 0.2 ng/mL (OR = 0.123; 95% CI = 0.020-0.762; P = 0.024) as shown in Table 5. As for patients received RAI with TgAb-negative, the ratio of metastatic LNs ≥ 25% was an independent predictor for off-Tg ≥1 ng/mL (OR = 20.997; 95% CI = 1.649-267.384; P = 0.019). However, no significant differences were found in the multivariate analysis for predictors of on-Tg ≥ 0.2 ng/mL.