Survival Analysis Cut-off

Hello guys,

I am doing a survival analysis using TCGA-BRCA project data. I am trying different cut-offs to separate my samples into high and low risk groups, but since it is my first time I would like to ask a question just to be fully sure that I am on the right track.

When I choose a cut-off based on an algorithm (not median like i’ve read in most papers) and I divide my patients based on that I get only 6 patients in the High-Risk group and around 900 in Low-Risk group. Using this criteria after I do my KM plot and ROC curve to validate its strength they are both very highly significant.
However, I wanted to know that despite these results being so significant, if I should continue down that path or ignore that strategy since one of the groups represents only 6/903 of my patients?

Thank you in advance!!!