I have a data set consisting of patients undergoing a treatment. The data set contains treatment start date, treatment end date, and date of death (if the patient has died). I also have a set of laboratory test results. The laboratory results are used to determine "disease progression" which may be assumed to have occurred at a specific point in time. The laboratory results are the only source of this information.
The study protocol defines a compound event defined to be the time from the start of treatment until "disease progression" or death, censoring at the end of study.
The analysis is to be done using a Kaplan-Meier approach.
None of the patients have been lost to follow-up however I have been told two things regarding the lab results:
- they are not recorded for some patients and
- the laboratory results where available are only until the end of treatment
Ignoring this will affect the analysis and probably bias the estimates.
I am interested in estimating the time to the compound event. There are no covariates involved. The issue for me is the uncertainty about the date of the compound event, caused by the laboratory data to be used for determining the "disease progression" date.
My question is how should I procede in the analysis in terms of censoring under the assumption that there is no relationship between the recording of laboratory results and the patient/treatment.
Specifically should I
a) censor those patients with lab results at the end of their treatment (when I know that the lab results are no longer available).
b) for patients with no lab results - how should I handle them - does censoring at the start of treatment make sense and should I do it? If not, what approach could I take?
I would be grateful for any pointers.