[R] cox model

[billemont@cegetel.net]

I'm a french medicine student and i work on oncology. I work about
treatment oh breast cancer. I have 3 sub group of patient. I made some
kaplan meyer survival curve, and i made a cox model.

On the survival curve, on the last observations there is a crossmatch of
the different survival curve at 150 month .
I study the validity of my model by study of residual by  study the
proportional risk. So i used Coxzph formula, but the global test is p<
0.05, so my model is not a  proportional risk.

Do you know how i can cut the cox model analysis before the 150 month,
wich are the time where the curves are  crossing?

Thank you for your Help

Dr Billemont