Statistical analysis
A descriptive analysis was performed. Mean/standard deviation & median/
interquartile range or frequency & percentage were reported for
continuous and categorical variables respectively. Comparisons of
demographic and clinical characteristics by lung metastases status
were conducted using Pearson Chi-square and Wilcoxon rank-sum tests
appropriately.
The incidence of lung metastases among hypo-pharyngeal cancer patients
was defined as the number of hypo-pharyngeal cancer patients diagnosed
with lung metastases divided by the total number of patients with
hypo-pharyngeal cancer. The 95%CI of incidences was reported using the
Wilson method. We also calculated incidences along with 95%CIs by age
group, race, sex, histological grade, AJCC stage, tumor size by groups,
metastases, and primary site.
A multivariable logistic regression model was conducted to evaluate the
association between lung metastases and age, race, sex, histological
grade, tumor size and primary site where both age and tumor size were
treated as continuous covariates. Presence of bone, brain, or liver
metastases at the time of cancer diagnosis is available in the SEER
database and was used to characterize the extent of systemic disease
among patients in this study.
In addition we performed a multivariable Cox Proportional Hazards
regression model to estimate survival time between patients with or
without lung metastases during a five year follow-up period while
controlling for the covariates listed above. Subjects who died of other
non- hypo-pharyngeal cancers and those who lost follow-up were censored.
Almost 35% of patients were missing tumor sizes; as a result multiple
imputation with 100 imputed datasets was performed. The results of these
models with or without multiple imputation were consistent and complete
case model results were reported.
All statistical analyses were performed using STATA statistical
software, Version 16.0 (College Station, TX) and R version 3.5.0.
Statistical significance was defined as two-sided alpha level at 5%.
This study was approved by the institutional review board at Zhongshan
Hospital of Fudan University; written and informed consent was waived.