A 66-year-old man was referred for elevated prostate specific antigen (PSA; 5.6 ng/ml) and underwent transperineal (TP) prostate biopsy that found low volume Gleason score 3+3=6 (ISUP Grade Group 1) prostate cancer (PCa). After a 15-month period of active surveillance the patient's PSA rose to 8.2 ng/ml and a multiparametric prostate magnetic resonance imaging (MRI) discovered 2 PI-RADS™ 5 lesions. The patient was rebiopsied using cognitive fusion, revealing extensive Gleason score 4+3=7 (ISUP Grade Group 3) PCa. He underwent a robotic assisted prostatectomy (without pelvic lymph node dissection) with histopathology demonstrating pT2c Gleason score 4+3=7 (ISUP Grade Group 3) and clear margins. PSA was undetectable at 3 months, then rose to 0.11 at 12 months, and 0.58 ng/ml at 18 months postoperatively.

The patient underwent a whole body gallium-68 prostate specific membrane antigen (PSMA) positron emission tomography/computerized tomography (PET-CT), which showed no evidence of PSMA avid PCa. The patient proceeded to prostate bed salvage radiotherapy (70Gy in 35 fractions) alone (no hormone therapy), which he tolerated with minimal toxicity. After treatment his PSA dropped to 0.08 ng/ml and 0.01 ng/ml at 1 and 2 years postradiation, respectively. Three and a half years after prostate bed salvage radiotherapy his PSA increased sharply to 0.79 ng/ml (PSA doubling time (PSAdt) 2.4 months) prompting a repeat whole body gallium-68 PSMA PET-CT. This time it was positive, demonstrating metastatic disease in a lymph node in the right internal iliac station (see figure). This metastatic deposit was treated with stereotactic radiotherapy (50Gy in 10 fractions) alone (no hormone therapy). At 4 months after treatment the patient has had no radiation toxicity and his PSA has dropped to 0.01 ng/ml.

Figure. PSMA PET/CT avidity in right lateral pelvic node in right internal iliac station consistent with metastatic lymph node (white arrow).

Early identification of recurrent disease is of critical importance for managing PCa after curative intent therapy. Visualization of metastases via PSMA PET-CT allows for metastasis directed therapies (MDT) such as stereotactic radiation treatment. PSMA PET-CT has demonstrated excellent results as an accurate diagnostic modality following biochemical recurrence. Importantly, PSA level and kinetics impact recurrence detection rate. Our case study patient underwent 2 PSMA PET scans 3.5 years apart, following a PSA rise with rapid PSAdt. In a study by Ceci et al a positive scan was demonstrated in 85% of patients with PSA less than 2 ng/ml and PSAdt less than 6.5 months. ¹ This is congruent with a retrospective study by Eiber et al that found pathological scans in 72.7% of men with PSA values between 0.5 to less than 1 ng/ml after radical prostatectomy. ² Additionally, PCa recurrence to the pelvic lymph nodes is best detected by PSMA PET-CT over other imaging modalities such as CT and MRI. ^3,4

According to EAU Guidelines, PSMA PET-CT is now indicated to investigate biochemical recurrence after prostatectomy when PSA is greater than 0.2. ⁵ It can precisely locate sites of local disease recurrence for salvage therapy or oligometastases for MDT. MDT may delay the need for systemic therapy and can sometimes be curative. ⁶