Do you recommend MRI pelvis/prostate in a patient with biochemical recurrence after XRT and negative axumin PET scan?

This is a difficult question to answer as the context is very important. If this is a younger patient with fast doubling time that warrants aggressive treatment, the answer will be different than in an older patient with a slow doubling time. The patient's particulars (co-morbid conditions, prior treatments, urinary function, size of the prostate, ...) will have a significant impact on the choice of imaging. The positive predictive value for recurrence in the prostate of MR after radiation is about 60-70%. The positive predictive value of a fluciclovine-PET/CT in the prostate is about 30-40%. I am not aware of any studies that have addressed the negative predictive value of either fluciclovine or MR in the prostate after radiation. The fluc...

If suitable for salvage local therapy and XRT was not delivered in the post-prostatectomy setting, then the answer is yes for the MRI. The intent of the MRI is to determine anatomically whether salvage local therapy can be reasonably delivered before obtaining biopsies.

There is a new published guideline from ASCO that is available in Epub by
Trabulsi EJ, et al. that specifically addresses your question. Excellent article for an overview with a rather thorough literature review. From the article an extremely reasonable algorithm for biochemical recurrence after XRT is under Figure 2.

Optimum Imaging Strategies for Advanced Prostate Cancer: ASCO Guideline. (Trabulsi EJ et al. J Clin Oncol. 2020 Jan [Epub ahead of print])

One word of caution wit...

Yes, if one is considering salvage prostatectomy or brachytherapy.