Would you recommend initiating a SGLT2i for proteinuria secondary to bevacizumab in a patient who has a sub-optimal response to an ACEi or ARB?

Obviously, SGLT2i were not studied in this setting. If the patient otherwise meets the criteria for approved uses of SGLT2i then it is reasonable to consider. The prescriber should make a careful assessment of the risk and risk factors for infections and monitor the Cr closely. An initial increase in Cr with initiation of the SGLT2i is expected but any subsequent increase in Cr should be evaluated given the concern for CPI AIN/AKI.

We don't have specific data for this scenario, but there is no reason to think that SGLT2i would not have a beneficial role though I agree with Dr. @Dr. First Last that risk/benefit needs to be weighed. At the same time, in this particular scenario, I'd carefully look at the time course of proteinuria, peak proteinuria as well as the degree of response to RAAS blockade to ascertain whether something other than VEGF nephrotoxicity is at play. We don't generally do a kidney biopsy on such patients but I have occasionally done so precisely when proteinuria was high grade (i.e., >4g) with less than stellar response to stopping the anti-VEGF agent and instituting RAAS blockade.

VEGFi-induced HTN/proteinuria is thought to involve the Endothelin-1 pathway and compared to SGLT2i, endothelin receptor antagonists may have an even more plausible role in such a patient. That also has not been specifically studied.