Mesorectal Lymph Node Metastases as Index Lesion in ⁶⁸Ga-PSMA-PET/CT Imaging for Recurrent Prostate Cancer

Purpose: Several studies have demonstrated an advantage of ⁶⁸Ga-PSMA-PET/CT as staging modality for detection of prostate cancer (PCa) metastases. Data concerning metastatic manifestation and impact on PCa development of mesorectal lymph nodes (MLN) is limited. Our investigation describes MLN metastases as index lesion in ⁶⁸Ga-PSMA PET/CT imaging for recurrent PCa. Methods: Twelve PCa patients with biochemical recurrence (BCR) after primary therapy who prospectively underwent a baseline ⁶⁸Ga-PSMA-PET/CT initially showed MLN metastases. Eight of these patients received a follow-up ⁶⁸Ga-PSMA-PET/CT to evaluate treatment response and further evolution. Prostate-specific antigen (PSA)-levels, changes in PSMA-uptake of MLN metastases and further ⁶⁸Ga-PSMA PET/CT findings were recorded. Results: Median PSA at the first ⁶⁸Ga-PSMA-PET/CT was 5.39 ng/ml. In all patients therapeutic management changed after the first ⁶⁸Ga-PSMA-PET/CT. Androgen deprivation therapy (ADT) was initiated in seven of eight patients, one patient restarted initial ADT. Three patients additionally received salvage radiation therapy (sRT) including the prostatic lodge and docetaxel chemotherapy was started in one case. At follow-up, a decrease of PSA-level was detected in all patients (median 2.05 ng/ml) after median 10 months. In six of eight patients we observed a decrease or complete regress of PSMA-uptake in MLN in the follow-up ⁶⁸Ga-PSMA-PET/CT. Conclusion: MLN metastases detected by ⁶⁸Ga-PSMA-PET/CT seem to be a relevant localization of tumor manifestation and may serve as index lesion in the treatment of recurrent PCa. Besides the known oncological benefits of ADT and sRT, in case of sole MLN metastases individualized therapy like salvage lymphadenectomy or RT with a defined radiation field could be options for these patients.