Determinants and Prognostic Impact of Extent of Surgery for Thyroid Microcarcinoma Restricted; Files Only

Wang, Danyang (Summer 2021)

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Background: Total thyroidectomy (TT) is the dominant surgical procedure in the management of thyroid microcarcinoma, despite the current guidelines suggesting that thyroid lobectomy (TL) alone is sufficient for localized microcarcinoma. This study primarily aimed to assess the possible demographic or clinical factors that may affect the decision on the extent of surgery for primary thyroid microcarcinoma.

Methods: Patients who were diagnosed with primary thyroid microcarcinoma between 2004 and 2016 were included from the U.S. National Cancer Institute Surveillance, Epidemiology, and End Results 18 registries database. Univariate and multivariate analyses using polytomous logistic regression were performed to analyze the association between demographic or clinical characteristics and the extent of surgery. The Kaplan-Meier method was used to estimate thyroid cancer related survival and the log-rank test was used to compare survival rates between groups. Multivariate analysis using Cox proportional hazards model was used to estimate the independent prognostic effect of surgery type on cause-specific survival (CSS).

Results: The cohort consisted of 45,495 patients. Overall, 76.8% of the patients underwent TT, 22.8% underwent TL, and 4.2% had no surgery. According to multivariate analysis, TL, compared to TT, was more frequently performed in patients with age > 65 years (odds ratio [OR]=1.19, 95% confidence interval [CI] 1.11-1.27) and other non-Hispanic races (OR=1.18, 95% CI 1.09-1.28), and less likely to be performed in females (OR=0.73, 95% CI 0.68-0.77), non-Hispanic blacks (OR=0.81, 95% CI 0.74-0.89), and those with higher-stage cancers (OR=0.23, 95% CI 0.20-0.25) and multifocal tumors (OR=0.40, 95% CI 0.38-0.42). Excellent 10-year CSS was observed following both TT and TL in patients with early-stage thyroid microcarcinoma and no difference in CSS was found between patients who underwent TT vs. TL.

Conclusions: TT remains the predominant surgical method for treating primary thyroid microcarcinoma and this trend has increased in recent years, despite a lack of evidence of survival advantage offered by more extensive surgical procedures. In order to improve the quality of life of the patients, reduce healthcare costs, and prevent overtreatment, TT should be performed on a selected group of patients with a high risk of tumor recurrence in the management of thyroid microcarcinoma.

Table of Contents

1. Introduction 1

2. Materials and Methods 2

2.1 Data Collection 2

2.1.1 Study Population 2

2.1.2 Covariates 4

2.2 Data Organization 4

2.3 Statistical Methods 5

2.3.1 Descriptive Analysis 5

2.3.2 Bivariate Associations Between Type of Surgery and Other Covariates 5

2.3.3 Multivariate Analysis 6

2.3.4 Survival Analysis 7

3. Results 8

3.1 Descriptive Statistics 8

3.2 Bivariate Associations Between Type of Surgery and Other Covariates 9

3.3 Multivariate Analysis 11

3.4 Survival 12

4. Discussion 14

4.1 Limitations 16

4.2 Conclusions 16

5. References 17

6. Tables & Figures 21

Table 1. Patient characteristics by surgery type 21

Table 2. Odds ratio estimates for univariate polytomous logistic regressions 23

Table 3. Odds ratio estimates for multivariate polytomous logistic regressions 24

Table 4. Odds ratio estimates for subgroup multivariate logistic regressions among patients with localized thyroid microcarcinoma and treated with surgery 25

Table 5. Hazard ratio estimates in Cox model based on death due to thyroid cancer by stage and surgery type 26

Figure 1. Flow chart of patient selection 27

Figure 2. Cause-specific survival by surgery group 28

7. Appendix 29

7.1 SAS code for data Organization 29

7.2 SAS code for Statistical analysis 38

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