Statistical analysis
Baseline characteristics of the studied population were described as
medians (ranges) for quantitative variables and numbers (percentages)
for qualitative variables. The time to OMT second events was plotted
using Kaplan-Meier curves. Baseline factors associated with OMT second
events were identified by univariate analysis using the log-rank test if
they were qualitative or by the Cox model if quantitative (such as age
at diagnosis). Univariate analysis on the type of surgery was based on
the population without missing data (6 cases excluded). Factors that
were associated with a p<0.10 in univariate analysis were
considered in a multivariate Cox model using a stepwise procedure for
entering and staying in the model. All statistical analyses were
performed with SAS software V9.4 (SAS Institute, NC, Cary), and a
p-value <0.05 was considered to denote statistical
significance.
This study was supported by the board of ethics committee (CLERS) and
conducted in accordance with the Declaration of Helsinki. Institutional
review board approval was obtained.