infile group futime number size rectime using c:\data\tumor.dat  (this command reads the data)

gen fail=1 if rectime!=. (create censoring indicator value=1 if recurrence observed)

replace fail=0 if rectime==.(replace censoring indicator value=0 if no recurrence)

replace rectime=futime if rectime==.(replace missing censor time by follow-up time)

stset rectime, failure(fail)(declare the data as survival data).

One subject with zero follow-up time was automatically excluded by Stata's stset command. User of other software may need to remove this subject explicitly. A censored case with zero follow-up time is not informative. A failure at time zero is not logical: one fails at least a very short while after getting started.