The cause of fever shoud be evaluated. No relation with bladder tumour

I dont think there is any relationship between bladder tumor existence and or or post surgery removal have with intake of PCM.  It's safest antipyreteics and even Analgesic.  But we should keep in mind that any medications ( in fact any human made things) are associated with side effects whichh may be reveal with single dose or may show after many doses. So always be careful while taking medications. But if it require then we can minimize these side effects if our other organs - like liver in PCM case fine.

Yes... Provided the liver functions were normal.....  also in assuming that the patient had an endoscopic removal of the tumor...

Can take it but need to know the reason of fever. There could be a surgical site infection