When monitoring the effectiveness of therapy using assessments of clinical, biochemical (e.g., PSA, ALP), and imaging findings in prostate cancer patients treated with androgen deprivation therapy, cytotoxic chemotherapy, hormone therapy, and palliative radiotherapy, as well as Ra-223 therapy [24,25,26,27,28,29], care must be taken regarding the so-called “flare effect”, which results from an early or transient rise in PSA level or tracer uptake during a bone scan procedure, followed by a later decline, especially in the early phase of treatment. Here, KLK3 is linked to prostate cancer.