A comparison of lobectomy and total thyroidectomy in patients with papillary thyroid microcarcinoma: a retrospective individual risk factor-matched cohort study

in European Journal of Endocrinology
Authors:
Hyemi KwonDepartments of Internal Medicine

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Min Ji JeonDepartments of Internal Medicine

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Won Gu KimDepartments of Internal Medicine

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Suyeon ParkDepartments of Internal Medicine

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Mijin KimDepartments of Internal Medicine

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Dong Eun SongPathology

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Tae-Yon SungSurgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

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Jong Ho YoonSurgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

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Suck Joon HongSurgery, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea

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Tae Yong KimDepartments of Internal Medicine

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Young Kee ShongDepartments of Internal Medicine

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Won Bae KimDepartments of Internal Medicine

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Free access

Objective

Papillary thyroid microcarcinoma (PTMC) accounts for most of the increase in thyroid cancer in recent decades. We compared clinical outcomes and surgical complications of lobectomy and total thyroidectomy (TT) in PTMC patients.

Design and methods

In this retrospective individual risk factor-matched cohort study, 2031 patients with PTMC were initially included. Patients who underwent lobectomy or TT were one-to-one matched according to individual risk factors, including age, sex, primary tumor size, extrathyroidal extension, multifocality and cervical lymph node (LN) metastasis.

Results

In total, 688 patients were assigned to each group. During the median 8.5 years of follow-up, 26 patients (3.8%) in the lobectomy group and 11 patients (1.6%) in the TT group had recurrences. The relative risk of recurrence was significantly less in the TT than that in the lobectomy group (hazard ratio (HR) 0.41; 95% confidence interval (CI) 0.21–0.81; P = 0.01). Most recurrences (84.6%) in the lobectomy group occurred in the contralateral lobe, and all patients were disease-free after completion of thyroidectomy. There were no significant differences in recurrence-free survival between the two groups after exclusion of contralateral lobe recurrences (HR, 2.75; 95% CI, 0.08–8.79; P = 0.08). There were significantly more patients with transient and permanent hypoparathyroidism in the TT than that in the lobectomy group (P < 0.001).

Conclusions

Lobectomy could be appropriate for most patients with PTMC when there is no evidence of extrathyroidal disease in the preoperative work-up. Preoperative and postoperative imaging studies are important for patients who undergo lobectomy for PTMC, because most recurrences are in the contralateral lobe.

Abstract

Objective

Papillary thyroid microcarcinoma (PTMC) accounts for most of the increase in thyroid cancer in recent decades. We compared clinical outcomes and surgical complications of lobectomy and total thyroidectomy (TT) in PTMC patients.

Design and methods

In this retrospective individual risk factor-matched cohort study, 2031 patients with PTMC were initially included. Patients who underwent lobectomy or TT were one-to-one matched according to individual risk factors, including age, sex, primary tumor size, extrathyroidal extension, multifocality and cervical lymph node (LN) metastasis.

Results

In total, 688 patients were assigned to each group. During the median 8.5 years of follow-up, 26 patients (3.8%) in the lobectomy group and 11 patients (1.6%) in the TT group had recurrences. The relative risk of recurrence was significantly less in the TT than that in the lobectomy group (hazard ratio (HR) 0.41; 95% confidence interval (CI) 0.21–0.81; P = 0.01). Most recurrences (84.6%) in the lobectomy group occurred in the contralateral lobe, and all patients were disease-free after completion of thyroidectomy. There were no significant differences in recurrence-free survival between the two groups after exclusion of contralateral lobe recurrences (HR, 2.75; 95% CI, 0.08–8.79; P = 0.08). There were significantly more patients with transient and permanent hypoparathyroidism in the TT than that in the lobectomy group (P < 0.001).

Conclusions

Lobectomy could be appropriate for most patients with PTMC when there is no evidence of extrathyroidal disease in the preoperative work-up. Preoperative and postoperative imaging studies are important for patients who undergo lobectomy for PTMC, because most recurrences are in the contralateral lobe.

Introduction

The incidence of thyroid cancer has recently increased worldwide. This increase has been predominantly attributed to papillary thyroid microcarcinoma (PTMC) (1, 2, 3, 4). PTMC is defined as a papillary thyroid carcinoma measuring equal or less than 1 cm in the greatest dimension (2). PTMC usually has an indolent course and excellent prognosis (5, 6, 7, 8). Disease-specific mortality rate of patients with PTMC who underwent treatment is less than 1%, loco-regional recurrence rate is 2–4% and distant recurrence rate is 1–2% (5, 6, 7, 8). The prognostic factors for recurrence in patients with PTMC were known such as age, large primary tumor size (>0.5 cm), presence of extrathyroidal extension, multifocal tumor and the presence of cervical lymph node (LN) metastasis (5, 6, 9, 10, 11, 12, 13, 14).

Because of its favorable outcomes, previous studies have suggested conservative strategies for evaluating and treating PTMCs (15, 16, 17, 18, 19). Recent American Thyroid Association (ATA) guidelines stated that PTMC had a low risk for structural recurrence (20). In one study, among 1235 patients with PTMCs who were underwent active surveillance, 5% of patients demonstrated increase in size of the tumor and 1.5% patients showed a novel appearance of LN metastasis on 5-year follow-up (17). ATA guidelines stated if surgery is chosen for patients with small thyroid cancer (<1 cm) without extrathyroidal extension and clinical N0, the initial surgical procedure should be a thyroid lobectomy unless there are clear indications to remove the contralateral lobe (20). A recent retrospective study demonstrated that total thyroidectomy (TT) significantly decreased the risk of overall loco-regional recurrences of PTMC patients (P < 0.001) and not the risk of loco-regional recurrence outside of the contralateral remnant lobe (P = 0.6) (6). However, there were significant differences in baseline clinicopathological characteristics such as age, sex ratio, primary tumor size and the proportion of extrathyroidal extension, multifocal tumors and LN metastasis between lobectomy and TT patients (6). To the best of our knowledge, no study has compared lobectomy and TT in PTMC patients with similar baseline clinical and pathological risk factors.

In this study, we aimed to compare the clinical outcomes and surgical complications in patients with PTMC according to surgical extent (lobectomy and TT) after individual risk factor matching. We applied a one-to-one matching method to control the risk factors that may affect the prognosis of PTMC and to minimize the selection bias in decisions for surgical extent.

Subjects and methods

Study design and patients

This retrospective cohort study consecutively included 2031 patients with PTMC who underwent initial thyroid surgery and routine prophylactic central compartment node dissection from 1998 to 2007 at Asan Medical Center in Seoul, Korea. Ninety-nine patients with lateral cervical LN metastasis (N1b) and 4 patients with distant metastasis (M1) at initial diagnosis were excluded. Of the 2031 patients, 755 (32%) underwent lobectomy, whereas 1276 (63%) underwent TT (Table 1). Patients who underwent lobectomy or TT were one-to-one matched according to individual risk factors including age, sex, primary tumor size, extrathyroidal extension, multifocality and central compartment LN metastasis (pN1a). Patients within 3 years of age were considered to be the same age. Primary tumors with size differences of less than 0.2 cm were considered to be the same size for one-to-one matching. As a result of individual risk factor matching, 688 patients were assigned to each group. We compared the clinical outcomes of 1376 patients with PTMC according to surgical extent. Clinicopathological features of PTMC patients who were excluded from the individual matching were described in Supplementary Table 2 (see section on supplementary data given at the end of this article). This study was approved by the Institutional Review Board of Asan Medical Center.

Table 1

Baseline clinicopathological features of patients with PTMC according to surgical extent. Continuous variables are presented as medians (inter-quartile range). Categorical variables are presented as numbers with percentages.

After individual matching
Lobectomy (n = 755) Total thyroidectomy (n = 1276) P value Lobectomy (n = 688) Total thyroidectomy (n = 688)
Age (year) 47 (40–53) 50 (42–56) <0.001a 47 (41–54) 47 (41–54)
 ≥45 year 423 (55) 855 (67) <0.001b 405 (59) 415 (60)
Sex (F) 672 (89) 1118 (88) 0.387b 628 (91) 628 (91)
Primary tumor size (cm) 0.6 (0.5–0.8) 0.7 (0.5–0.8) <0.001a 0.6 (0.5–0.8) 0.6 (0.5–0.8)
 >0.5 cm 451 (60) 885 (69) <0.001b 415 (60) 435 (63)
Extrathyroidal extension (Y) 274 (36) 621 (49) <0.001b 261 (38) 261 (38)
Multifocality (Y) 79 (10) 309 (24) <0.001b 69 (10) 69 (10)
Cervical LN metastasis (Y) 212 (28) 403 (32) 0.107b 178 (26) 178 (26)

P value was estimated by Mann–Whitney U test; bP value was estimated by χ2 test.

LN, lymph node.

Management and follow-up protocol

The protocol was shared at our center to maintain consistent treatment and follow-up for all patients, as previously reported (5, 21, 22). Routine preoperative neck ultrasonography (US) was done in all the patients. If they had indeterminate or suspicious thyroid nodules in contralateral lobe, the nodules were evaluated by US-guided fine-needle aspiration cytology (FNAC) before thyroid surgery. The surgical extent was determined depending on patient preference and the decision of the surgeon at the time of surgery. Routine prophylactic ipsilateral central compartment LN dissection was performed for patients who underwent lobectomy. Prophylactic ipsilateral or bilateral central compartment LN dissection was performed for patients who underwent total thyroidectomy. Therapeutic neck dissection was performed when metastatic cervical LNs were confirmed preoperatively or suspicious metastatic LNs were detected at the time of surgery. Subsequent radioactive iodine (RAI) remnant ablation therapy was conducted for some patients with PTMC who underwent TT. After initial therapy, patients who were underwent total thyroidectomy took levothyroxine for TSH suppression. In lobectomy group, 262 patients (35%) took levothyroxine for TSH suppression, and 70 patients (9%) took levothyroxine for substitutive therapy. All patients were regularly followed up with physical examinations, thyroid function tests, serum thyroglobulin (Tg) and anti-Tg antibody measurement every 6–12 months for at least 2 years after surgery. Neck US was performed during the first 6–12 months after initial therapy and repeated thereafter at 12- to 24-month intervals. Diagnostic whole-body scans (WBS) were performed after TT and RAI remnant ablation. Additional diagnostic imaging studies, such as computed tomography (CT), magnetic resonance imaging (MRI) or whole-body fluoro-deoxyglucose (FDG)-positron emission tomography (PET) were performed to detect recurrence or distant metastasis in some patients.

Definitions

Loco-regional recurrence was defined as pathologically or cytologically proven lesions based on imaging studies. Recurrence-free survival (RFS) was defined as the time interval between initial surgery and the detection of structural persistent/recurrent disease. Transient hypoparathyroidism was defined as postoperative hypocalcemia with albumin-corrected serum total calcium <8.0 mg/dL (2.0 mmol/L) and/or the need for calcium/vitamin D supplements to maintain serum calcium within the reference range or to prevent symptoms (23, 24). Permanent hypoparathyroidism was defined as persistent hypocalcemia 12 months after surgery requiring calcium and vitamin D supplements (23).

Statistical analysis

For individual risk factor matching and analysis, Greedy method was used by SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Several statistical analyses were conducted using SPSS, version 21.0 (SPSS). Graphs were produced using Prism, version 5.01 (GraphPad Software). Continuous variables are presented as medians with inter-quartile ranges (IQR). Categorical variables are presented as numbers with percentages. The Mann–Whitney U test was used to compare continuous variables. The chi-square test and Fisher’s exact test were used to compare categorical variables. In the matched data set, risks of recurrence were compared using Cox regression models, with robust standard errors that accounted for the clustering of matched pairs. The Cox proportional hazards model with hazard ratios (HRs) and 95% confidence intervals (CIs) was used to evaluate risks of recurrence according to surgical extent. RFS curves were constructed using the Kaplan–Meier method, and the log-rank test was used to evaluate differences in the RFSs between groups. P values <0.05 were considered statistically significant. All P values were two-sided.

Results

Baseline characteristics before individual matching

The baseline characteristics of the 2031 PTMC patients according to surgical extent are listed in Table 1. The median age of the lobectomy group was significantly younger than that of the TT group (P < 0.001). There were no statistically significant differences in sex ratio between the two groups. Median primary tumor size in the lobectomy group was significantly smaller than that in the TT group (0.6 cm vs 0.7 cm, P < 0.001). The proportions of extrathyroidal extension and multifocality were significantly higher in the TT group than that in the lobectomy group. Extrathyroidal extension was present in 274 patients in the lobectomy group (36%) and 621 patients (49%) in the TT group (P < 0.001). Patients with multifocal tumors comprised 10% and 24% in the lobectomy and TT groups respectively (P < 0.001). There were no significant differences in the proportion of patients with cervical LN metastasis.

Clinical outcomes according to each risk factor before individual matching

The clinical outcomes of PTMC patients were evaluated according to each risk factor (Table 2). In univariate analyses, there were no significant associations between recurrence rates and surgical extent, primary tumor size and extrathyroidal extension. However, older patients had fewer recurrences than younger patients (HR: 0.96, 95% CI: 0.93–0.98; P < 0.001). Female had fewer recurrences than male (HR: 0.39, 95% CI: 0.23–0.68; P = 0.001). Multifocal tumor (HR: 1.85, 95% CI: 1.11–3.08; P = 0.02) and cervical LN metastasis (HR: 2.32, 95% CI: 1.45–3.71; P < 0.001) were associated with more recurrences of PTMC. In multivariate analysis models 1 and 2, TT was not associated with the risk of recurrence. Younger age, male gender, multifocality and cervical LN metastasis were independent risk factors for recurrences in patients with PTMC. These variables were included in individual risk factor matching.

Table 2

Clinical outcomes of PTMC patients according to each risk factor.

Univariate analysis (n = 2031) Multivariate analysis 1a (n = 2031) Multivariate analysis 2b (n = 2031) Matched data analysis (n = 1376)c
95% CI 95% CI 95% CI 95% CI
HR Lower Upper P value HR Lower Upper P value HR Lower Upper P value HR Lower Upper P value
Surgical extent (TT) 0.73 0.45 1.16 0.18 0.68 0.42 1.1 0.11 0.71 0.43 1.15 0.16 0.41 0.21 0.81 0.01
Age (year) 0.96 0.93 0.98 <0.001 0.96 0.93 0.98 0.001
 ≥45 year 0.31 0.19 0.51 <0.001 0.34 0.21 0.56 <0.001
Sex (female) 0.39 0.23 0.68 0.001 0.43 0.25 0.75 0.003 0.47 0.27 0.82 0.008
Primary tumor size 2.64 0.94 7.44 0.07
 >0.5 cm 1.18 0.71 1.97 0.52
ETE (Y) 1.47 0.92 2.35 0.11
Multifocality (Y) 1.85 1.11 3.08 0.02 2 1.18 3.39 0.01 1.93 1.14 3.27 0.01
LN metastasis (Y) 2.32 1.45 3.71 <0.001 1.91 1.19 3.08 0.008 1.91 1.91 3.07 0.008

Multivariate analysis 1 was adjusted after backward elimination of age, sex, primary tumor size, ETE, multifocality and LN metastasis; bmultivariate analysis 2 was adjusted after backward elimination of age ≥45, sex, primary tumor size >0.5 cm, ETE, multifocality and LN metastasis; cin the matched data set, the risks of recurrence were compared with the use of Cox regression models, with robust standard errors that accounted for the clustering of matched pairs.

CI, confidence interval; ETE, extrathyroidal extension; HR, hazard ratio; LN, lymph node; TT, total thyroidectomy.

Clinicopathological features and clinical outcomes according to surgical extent after individual risk factor matching

Patients who underwent lobectomy or TT were one-to-one matched according to individual risk factors. The baseline characteristics of 688 patients in each group were similarly adjusted (Table 1). The median age was 47 years, and the median primary tumor size was 0.6 cm. In all, 38% of patients had extrathyroidal extension, 10% patients had multifocal PTMCs and 26% had cervical LN metastasis. After individual matching, the clinical outcomes of the patients were evaluated according to surgical extent. During the median 8.5 years of follow-up, 26 patients (3.8%) in the lobectomy group and 11 patients (1.6%) in the TT group had recurrences (Table 3). There were significantly fewer recurrences in the TT group than that in the lobectomy group (HR: 0.41, 95% CI: 0.21–0.81; P = 0.01).

Table 3

Types of recurrences in PTMC patients (n = 1376) according to surgical extent.

Type of recurrence Lobectomy (n = 688) Total thyroidectomy (n = 688)
Total recurrences (n) 26 11
Contralateral lobe (n) 22 0
Median durationa (year) (IQR) 4.4 (3.0–5.9)
Operation bed (n) 0 1
Median durationa (year) (IQR) 5.0
Lateral cervical LN (n) 4 10
Median durationa (year) (IQR) 2.9 (1.5–4.4) 2.7 (1.6–3.2)

Median duration was defined as the median time interval between the initial surgery and the detection of structural persistent/recurrent disease.

IQR, inter-quartile range; LN, lymph node.

Most recurrences (84.6%, 22 of 26 patients) in the lobectomy group occurred in the contralateral lobe (Table 3 and Supplementary Table 1). The median duration between the initial thyroid surgery and the detection of recurrence was 4.4 years. In the lobectomy group, only 4 recurrences occurred in lateral cervical LNs. In the TT group, 1 patient had a recurred disease at operation bed and the remaining 10 patients had lateral cervical LN recurrences (Supplementary Table 1). All patients with recurrences remained in a disease-free state after completion thyroidectomy and/or therapeutic neck dissection during a median 5.7 years (IQR 3.7–7.8) of follow-up.

In the lobectomy group, 122 patients (18%) had bilateral nodules in preoperative neck US. The proportion of bilateral nodules in patients with recurrence was 23% (6 of 26) and 18% (116 of 662) in patients without recurrence. There was no significant difference in bilateral nodules between patients who underwent lobectomy with or without recurrence (P = 0.5).

Sixty-nine of the 688 patients (10%) who were treated with lobectomy had multifocal PTC in pathological analysis of surgical specimen. Twenty-six of 688 patients had recurrent PTC and only two patients with multifocal PTC had recurrent PTC in our study. There was no significant correlation between multifocality and recurrence in lobectomy group (P = 0.7).

Recurrence-free survival according to surgical extent

Patients who underwent TT had better RFS than those who underwent lobectomy (P = 0.01; Fig. 1A). We also compared RFSs according to surgical extent, after the exclusion of contralateral lobe recurrences, which were the most types of recurrence in the lobectomy group. There were no significant differences in RFSs between the two groups (HR: 2.75, 95% CI: 0.08–8.79; P = 0.08; Fig. 1B).

Figure 1
Figure 1

(A) Recurrence-free survival (RFS) according to surgical extent. Patients with PTMC who underwent total thyroidectomy demonstrated improved RFS compared to patients who underwent lobectomy (P = 0.01). (B) RFS according to surgical extent after the exclusion of patients with contralateral lobe recurrence who were disease free after completion thyroidectomy. There were no significant differences in RFS according to surgical extent after the exclusion of contralateral lobe recurrences. P values were determined using the log-rank test. A full colour version of this figure is available at http://dx.doi.org/10.1530/EJE-16-0845.

Citation: European Journal of Endocrinology 176, 4; 10.1530/EJE-16-0845

Complications according to surgical extent

We compared the complication rates of the lobectomy and TT groups (Table 4). There were no significant differences in postoperative bleeding/hematoma or recurrent laryngeal nerve injury in both groups before and after individual risk factor matching. However, patients who underwent TT had significantly more transient (103 of 688 patients, 15% after matching) and permanent (12 of 688 patients, 1.7% after matching) hypoparathyroidism (P < 0.001).

Table 4

Surgical complications according to surgical extent.

After individual matching
Lobectomy (n = 755) Total thyroidectomy (n = 1276) P-valuea Lobectomy (n = 688) Total thyroidectomy (n = 688) P-valuea
Total complications 8 (1) 213 (17) <0.001 7 (1) 124 (18) <0.001
Bleeding 7 (1) 13 (1) 0.8 5 (0.7) 7 (1) 0.6
Hypoparathyroidism 0 193 (15) <0.001 0 115 (17) <0.001
 Transient 0 170 (13) 0 103 (15)
 Permanent 0 23 (1.8) 0 12 (1.7)
RLN injury 2 (0.3) 12 (0.9) 0.1 2 (0.3) 4 (0.6) 0.7

P value estimated by χ2 test.

RNL, recurrent laryngeal nerve.

Discussion

In this retrospective matched cohort study, we evaluated the clinical outcomes and surgical complications of PTMC patients according to surgical extent. Patients who underwent lobectomy or TT were one-to-one matched according to individual risk factors, including age, sex, primary tumor size, extrathyroidal extension, multifocality and central compartment LN metastasis (pN1a). TT for patients with PTMC improved RFS (P = 0.01). However, patients who underwent TT had more transient and permanent hypoparathyroidism. Most recurrences (84.6%, 22 of 26 patients) in patients who underwent lobectomy occurred in the contralateral lobe of the thyroid, and these patients remained disease-free after completion thyroidectomy. After the exclusion of contralateral lobe recurrences, there were no significant differences in RFSs between the lobectomy and TT groups. These findings suggest that lobectomy is an appropriate surgical extent for most patients with PTMC when clinical cervical LN metastasis is excluded in preoperative imaging studies. Preoperative and postoperative imaging studies are very important when thyroid lobectomy is applied to patients with PTMC.

Most patients with PTMC demonstrated excellent clinical outcomes, and all PTMC patients with recurrences could reach a disease-free state after re-operation. These findings are consistent with previous studies (5, 6, 7, 8, 10, 11, 12). In multivariate analyses, younger age, male gender, multifocality and cervical LN metastasis were related to recurrence of PTMC, as previously reported (5, 6, 9, 10, 11, 12, 13, 14). The median age of the TT group was significantly older, and the median primary tumor size was significantly larger than those of the lobectomy group (P < 0.001). Extrathyroidal extension, multifocality and central cervical LN metastasis (N1a) were also more frequent in the TT group. These differences in baseline clinicopathological features between the two groups were the main limitation to the appropriate comparison of surgical extent. In general, more extensive surgical approach tends to be selected for patients with more risk factors. However, this study was able to overcome this limitation by using the individual risk factor matching method to compare clinical outcomes according to surgical extent in balanced subjects.

In this study, TT for patients with PTMC was able to improve RFS (P = 0.01). However, there were no significant differences in RFS between the lobectomy and TT group after the exclusion of contralateral lobe recurrences. Several retrospective studies have suggested that TT can improve survival rates, decrease recurrence rates, make use of RAI remnant ablation and facilitate follow-up with diagnostic WBS and serum Tg (25, 26, 27). However, recent studies have demonstrated that clinical outcomes of lobectomy are not inferior to those of TT (20, 28, 29, 30). A study using the SEER database demonstrated no difference in 10-year overall survival (90.8% for lobectomy vs 90.4% for TT) or 10-year cancer-specific survival (98.6% for lobectomy vs 96.8% for TT) between lobectomy and TT (29). For these reasons, the surgical management paradigm has moved away from TT toward conservative strategies such as thyroid lobectomy for patients with low-risk PTMC (20).

Most recurrences in the lobectomy group occurred in the contralateral lobe. All the study patients underwent preoperative US, and indeterminate or suspicious thyroid nodules in contralateral lobe were evaluated by US-guided FNAC before surgery. Median duration for detection of recurrence was 4.4 years. Considering that we routinely followed up the patients every 6–12 months with neck US, the recurrent lesions should be newly developed after initial surgery.

The surgical risks of TT are known to be significantly higher than those of lobectomy from previous studies (31, 32). In a recent meta-analysis, the relative risk (RR) of hemorrhage/hematoma after TT was 2.6 (31). There were more transient (RR = 10.7) and permanent (RR = 3.2) hypocalcemia and recurrent laryngeal nerve injuries (RR = 1.9) in patients who underwent TT (31). Even high-volume surgeons have more postoperative complications when performing TT than performing lobectomy (32). Considering that the fundamental goals of treatment for patients with differentiated thyroid cancer are to improve survival and reduce recurrence/persistence as well as to minimize treatment-related morbidity, it is also important to reduce the complications associated with surgery (20).

This study had several limitations. There was the possibility of selection bias due to its retrospective nature and the involvement of only our single tertiary referral center. For individual risk factor matching, we excluded 67 patients in the lobectomy group and 588 patients in TT group (Supplementary Table 2). This approach may lead to a substantial error. Because we included patients from the early 2000s, about 63% of patients underwent TT. Among them, 87% of patients received RAI remnant ablation with median dose of 2.8 GBq (1.1–5.6). We were not able to evaluate the effects of RAI remnant ablation on clinical outcomes. However, all recurrences in our matched cohort were detected by regular neck US. The influences of serum Tg measurement after TT and remnant ablation were minimized for the detection of recurrent disease in our study. In addition, prophylactic central compartment LN dissection was performed in our study patient, and we could have definitely known the pathological N staging and used this information for risk factor matching in the two groups. Notably, this study is the first to compare clinical outcomes and surgical complications in PTMC patients managed by a uniform protocol at a single institution according to surgical extent applying an individual risk factor matching method.

In conclusion, most patients with PTMC demonstrated excellent clinical outcomes. Lobectomy could be an appropriate surgical extent for most patients with PTMC when there is no evidence of bilateral tumors or extrathyroidal disease in preoperative work-up. Most recurrences in patients who underwent lobectomy occurred in the contralateral lobe. There was no difference in RFS between the lobectomy and TT groups after the exclusion of patients with contralateral lobe recurrences who were disease free after completion thyroidectomy. Preoperative and postoperative imaging studies are important for patients who undergo lobectomy for PTMC because most recurrences are in the contralateral lobe.

Supplementary data

This is linked to the online version of the paper at http://dx.doi.org/©10.1530/EJE-16-0845.

Declaration of interest

The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.

Funding

This study was supported by a grant from the Korean Health Technology R&D project, Ministry of Health & Welfare, Republic of Korea (HC15C3372). This study was presented at a Young Investigator Session of the 39th annual meeting of the European Thyroid Association in Copenhagen, Denmark.

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    (A) Recurrence-free survival (RFS) according to surgical extent. Patients with PTMC who underwent total thyroidectomy demonstrated improved RFS compared to patients who underwent lobectomy (P = 0.01). (B) RFS according to surgical extent after the exclusion of patients with contralateral lobe recurrence who were disease free after completion thyroidectomy. There were no significant differences in RFS according to surgical extent after the exclusion of contralateral lobe recurrences. P values were determined using the log-rank test. A full colour version of this figure is available at http://dx.doi.org/10.1530/EJE-16-0845.