I am trying to vertically truncate Kaplan-Meier survival curves when they reach a certain threshold level of survival probability.

For example, in the basic K-M curve generated by:

Code:
sysuse cancer, clear
sts graph ,                                       ///
    ylab(0 "0" .25 "25" .5 "50" .75 "75" 1 "100") ///
    ytitle("survival probability (percent)")
...how could I tell Stata to vertically truncate the curve when survival probability reaches below 25%?

I know a hacky way of doing it is to manually eyeball when the curve hits below my threshold, and then set tmax accordingly (e.g. in this case tmax(32)). However, this would not work when I have multiple groups, each with a different point at which they cross the vertical threshold.

Moreover, I do not want to limit the y-axis to go from my threshold to 100, I would still like to display 0-100%, but with the curves truncated below my threshold.

Thank you in advance for any help.

EDIT: I would like to also add that I am interested in finding out how to do this truncation for when either a fractional threshold for survival is reached or an absolute threshold is reached. For example, how to tell Stata to stop the curve when fewer than 20 subjects or fewer than 25% of the original cohort are at risk.