I am a student conducting a gene expression analysis project using the gene expression data and the event free survival time for 249 cancer patients. I am applying the Cox Regression method to this data. However, I only have expression data from the tumor tissue (I do not have "normal" or "control" expression values).
I was under the impression that this would not be an issue and that I would still be able to conduct the survival analysis because I have the event-free survival times, state (dead or alive), and gene expression tumor data for all these patients and I am just looking for genes whose expression seems to affect the survival time.
However, as time goes on I am feeling a bit more doubtful and I would really appreciate it if someone would be able to tell me whether it is still alright to conduct a survival analysis as I have been doing without "control" data or two different expression groups (tumor and normal).
Thank you very much!