Common Iliac Node-Positive Prostate Cancer Treated With Curative Radiation Therapy: N1 or M1a?

Abstract

Common iliac (CI) nodes are staged as (oligo)metastatic M1a for prostate cancer. Whether outcomes of pelvic node-positive (cN1) differ from CI node-positive (CI-M1a) prostate cancer after curative treatment is unclear. The present study compares outcomes in patients treated with radical whole pelvic radiation therapy (RT) and long-term androgen deprivation therapy (ADT). Patients with a node-positive adenocarcinoma prostate were identified, either CI-M1a or cN1, from a prospectively maintained database. More than 75% of patients were staged with Gallium (Ga) 68 prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) at the time of diagnosis. All patients received long-term ADT and moderately or extremely hypofractionated RT to the prostate and pelvis, including the CI region. At the time of biochemical failure (BCF), restaging was done with Ga68-PSMA-PET/CT to establish the patterns of failure. The CI-M1a cohort was classified as proximal or distal CI nodal location, and studied for outcomes. Of the 130 patients analyzed, 87 had cN1 and 43 had CI-M1a stage disease. The median duration of ADT before RT was 7 months, and total duration was at least 24 months. The majority of patients (65%) had Gleason grade group IV to V, and 75% had ≥T3 disease. After a median follow up of 61 months, BCF in the 2 groups was similar (cN1: n=21 of 87; 24.1%; CI-M1a: n=11 of 43; 25.6%; P=.86). At the time of BCF, restaging Ga68-PSMA-PET/CT located distant metastases in 20 of 32 patients (63%; 57% in cN1 and 73% in CI-M1a; P=.47). In addition, the 5-year biochemical failure-free (cN1: 77.4%; CI-M1a: 70.4%; P=.43), distant metastasis-free (cN1: 86.9%; CI-M1a: 79.4%; P=.23), and overall (cN1: 92.6%; CI-M1a 90.1%; P=.80) survival were similar in the 2 groups. Outcomes within CI-M1a were similar for proximal versus distal CI nodal location and 5-year biochemical failure-free survival (73.6% vs 58.6%; P=.81). Patients with oligometastatic CI-M1a and cN1 prostate cancer showed similar outcomes when treated with curative whole pelvic RT and long-term ADT. The treatment for these oligometastatic patients should be prospectively evaluated.