Response: Comment on searching for prognostic markers for stage I epithelial ovarian cancer: A role for systemic inflammatory markers

We thank Dr Tang for their appreciation of our study which reported the potential prognostic role of some systemic inflammatory indexes for stage I ovarian cancers.1 Our results are in line with another re -cent study that investigated this specific issue.2We are aware that there is a general rule of thumb to use one covariate for every 10 outcome events in univariate or multivariate regression analyses. However, some observations must be made:1. Our study involves a relatively large cohort of stage I ovarian cancer, a rare tumor that typically has a favorable prognosis.Consequently, it is challenging to have very large study cohorts with a high number of events (recurrences or deaths of disease).These are a common issue when studying rare diseases.32. The rule regarding the number of outcomes per covariate is not mandatory. Statistical studies are showing that regression analyses can be performed even with fewer than 10 events per covariate. 4,53. Most published papers on rare tumors do not meet the assumption of one covariate for 10 outcome events. This also holds for other studies on prognostic factors for early-stage ovarian cancer. 2,6–10In conclusion, previous statistical and clinical studies support the use of Cox regression analysis despite there being fewer than 10events per variable. The authors of this study do not have any specific concerns regarding the statistical methods employed