Effect of prior thyroid cancer on survival from primary liver cancer: a study based on the SEER database

Study design and population

In this retrospective cohort study, we selected patients with PLC (the International Classification of Diseases for OncologyThird Edition [ICD-O-3] code: C22.0, liver; C22.1, intrahepatic bile duct) from the SEER database in 2004 and 2016 based on the November 2018 submission. The SEER database provides comprehensive patient data extracted from 18 geographically diverse populations that represent populations rural, urban and regional. Exclusion criteria were: (1) patients with a history of liver cancer; (2) loss of patient demographic information; (3)

Data Selection

We collected variables of age, gender (female or male), race (white, black, other), marital status [married (including common law) or not married]tumor size (less than 5 cm; greater than or equal to 5 cm; unknown), positive regional lymph nodes (yes; no; unknown), primary site (ICD-O-3, code C22.0 or C22.1), radiotherapy (none or unknown; yes), surgery (none or unknown; surgery performed), chemotherapy (none or unknown; yes), histological grade (grade I, well differentiated; grade II, moderately differentiated; grade III, poorly differentiated; grade IV, undifferentiated; unknown), American Joint Committee on Cancer (AJCC) status T (T1; T2; T3; T4; unknown), AJCC status N (N0; N1; unknown), AJCC status M (M0; M1 ; unknown), historical SEER stage (local; regional; remote; unknown), month of survival, vital status (alive or dead), SEER classification of causes of death (alive; death due to liver cancer; death due to other reason).

Variable Definitions

The primary site code (C22.0, liver) and ICD-O-3 histology codes were used to identify cases of hepatocellular carcinoma: 8170 to 8175. The primary site code (C22.0, liver ) and the ICD-O-3 histological codes of intrahepatic cholangiocarcinoma cases were 8160. Prior thyroid cancer was defined as a diagnosis of thyroid cancer (ICD-O-3 primary site code: C73. 9, thyroid gland) before patients were diagnosed with liver cancer.

Survival status of eligible patients was divided into three groups: (1) PLC-specific death; (2) death from other causes; (3) alive.

statistical analyzes

Propensity score matching (PSM) is a commonly used statistical method that establishes a new control group by eliminating outlier control subjects to reduce unwanted influences of covariates and correctly measure the predicted variable.20. We used PSM with a thickness value of 0.1 and a ratio of 1:10 for matching, i.e., each patient with previous thyroid cancer was matched according to the age and sex with 10 patients without prior thyroid cancer (Supplementary Table 1).

The Kolmogorov-Smirnov normality test was used for the measurement data. And the measurement data of normal distribution was described as mean ± standard deviation (mean ± SD), while the measurement data of non-normal distribution was presented as median and quartile [M (Q1, Q3)]. And an independent sample you essay and Mann–Whitney you rank sum test were performed, respectively. Count data manifested as cases and the ratio of constituents [n (%)] and were compared using the chi-square test or Fisher’s exact test.

The Cox proportional hazard model was used to explore the effect of previous thyroid cancer on PLC-specific risk of death. And the product-limit (KM) method was used to plot the curve of the cumulative incidence function. In the concurrent risk model, prior thyroid cancer was taken as the primary variable, month of survival, and survival status (i.e. Model 1 was an undusted model. Model 2 was adjusted for the age and sex, and model 3 was adjusted for all confounders i.e. age, sex, race, marital status, tumor size, regional lymph nodes positive, primary site, histological groupings, radiotherapy, surgery, chemotherapy, histology, grade, AJCC T status, AJCC N status, AJCC M status, historical SEER stage.

SAS software (SAS Institute Inc., Cary, NC, USA; version 9.4) was used for all analyses. All statistical tests were two-sided and P

Ethical statements

Our data comes from the SEER database. Since all database subjects were anonymous, informed consent and ethical approval were not required. All methods were performed in accordance with current guidelines and regulations.

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