When giving FOLFOX/FOLFIRI and skipping 5FU bolus, do you still give leucovorin?

In general, if I am not giving the 5-FU bolus, I will also not give the leucovorin. The purpose of the leucovorin is to increase the time that 5-FU given by bolus binds to thymidylate synthase. Since the 5-FU bolus is being withheld, the leucovorin has limited purpose, as the 5-FU continuous infusion is at steady state for 2 days.

I respectfully agree with @Dr. First Last, and this was my belief until recently reviewing this topic. Currently I am not sure.

So taking the other side of the argument, is there clinical data available to convince us otherwise, that LV is still of some benefit in infusional 5FU regimens?

From this study in JCO 2003, improved PFS and ORR with LV + 5 FU 24 hour infusion vs 5FU 24 hour infusion alone, although no OS benefit and increased toxicity with the 5FU CI 24 hour and LV arm.

Also, the mFOLFIRI...

The same principle applies to LV with 5FU in liposomal irinotecan for pancreatic cancer.