The principal aim of this study is to determine if PET/MRI imaging with 18-F fluciclovine (Axumin) identifies those men with false negative MRI fusion targeted biopsy (MRFTB) of PI-RADS 4 and 5 lesions. PI-RADS 4 and 5 MRI lesions are highly suspicious for clinically significant prostate cancer and require future repeat MRI imaging and possible repeat prostate biopsy depending on the results of the repeat MRI. Men, who had negative MRFTB within past 12 months of PI- RADS 4 or 5 MRI lesion will be included in this diagnostic study. The repeat MRI is standard of care at NYU Langone Health. The investigation aspect of the study is to perform an Axumin scan the same day as the MRI. Those men with persistent highly suspicious lesions will under MRFTB. The biopsy results will be compared with intensity of Axumin uptake within the prostate. The urologist will have the discretion to biopsy Axumin avid lesions not detected by MRI.

Inclusion Criteria:

• The participant has undergone MRFTB of an MRI lesion at the Department of Urology or at NYU Langone Health within past 12 months and has signed informed consent to participate in the NYU Urology prostate biopsy database.
• The most recent MRFTB of a PIRADS 4 or 5 lesion did not show clinically significant prostate cancer.

Exclusion Criteria:

• The urologist who performed the initial MRFTB does not feel a repeat MRI is indicated.
• Any contraindication to prostate biopsy including untreated urinary tract infection
• Prior allergic reaction to axumin
• Patient refuses MRI

The objective of the study is: to determine if PET imaging with 18-F fluciclovine identifies those men with prior negative MRFTBs of PI-RADS 4&5