Following treatment, other imaging tools, such as fluorodeoxyglucose-positron emission tomography (FDG-PET), prostate-specific membrane antigen (PMSA)-PET, and fluoride-PET, can be useful to assess tumor load reduction, particularly in patients showing increased PSA, which is helpful for differential diagnosis between progression and pseudo-progression (related to PSA flare phenomenon) [27,28,29]. The gene discussed is KLK3; the disease is neoplasm.