Would you change treatment in a patient with metastatic CRPC on PARP inhibitor with rising PSA but negative Axumin PET scan?

Short Answer:

No

Medium Answer:

The surrogacy of PSA as an intermediate endpoint in both localized prostate cancer and metastatic prostate cancer has been problematic. Multiple variations have been explored and tested including PSA doubling time (PSADT), PSA nadir, absolute PSA level, etc. None have demonstrated surrogacy for overall survival (OS). Certainly, some of these endpoints have shown general prognostic significance such as PSA nadir (See Kwak et al., PMID 12187207; Annual ASCO meeting ...

I agree with @Dr. First Last, however, I am curious that Axumin scan was performed to assess disease progression in CRPC which was already metastatic. Even if it was done, I don't think PARP inhibitors can achieve CR on Axumin scan. Likely, this particular patient may have small volume LN metastatic progression which became undetectable on PET scan.