I think the first and subseqent statements should be expanded to work correctly:
(Clinical T = "T1a" or Clinical T = "T1b") and Clinical N = "N0" and Clinical M = "M0" ;
The way you have it, ("T1a" or "T1b") will always result in True (1) and I would guess that Clincai T = 1 never occurs.
I also noticed that the last line that ends with …("'M1a" or "M1b")) is not followed by the result (e.g. " ; "Stage IIIC"). And there is no default result included. The default result is optional but may help simplify your Case statement.
You may be able to simplify the case statement further although it would take more thought than I have time for at the moment.
That works a treat! Thanks very much for your answer.
I'm trying to accomplish the same for breast cancer staging...if you have succeeded with the function, would you care to share the finished version, so I could adapt it to my database?