Evaluation of metastases-directed therapy for oligometastatic prostate cancer, by Ahmed El-Modir, consultant oncologist, Birmingham Prostate Clinic

Dr Ahmed El-Modir

In recent years, there have been some very positive developments in the prostate cancer field for men with advanced disease. One of these is a new approach for patients with oligometastatic disease (sometimes also known as early metastatic disease). To start with a definition: oligometastatic disease is the term used when there is some distant relapse (secondary cancer in another part of the body away from the primary site), but in a small number of locations, at an early stage which is amenable to treatment. We are changing the way that we understand and explain oligometastatic disease: moving away from an end-stage prognosis that can be frightening and/or difficult for patients and considering it more like a chronic condition which will not be cured but can be managed and controlled in a number of ways.

One of those management approaches is Metastases-directed therapy. This is an option that has become possible thanks to advances in imaging technology. The scenario is this: patients have had primary treatment but a rising PSA (prostate specific antigen) indicates treatment has not cleared or fully controlled the disease. Nor do they have full metastatic disease; the distant relapses are usually too small to be visible on bone scans. Advances in imaging mean we can offer these patients a PET (Positron-emission tomography) scan using a special tracer (PSMA or Choline) which can detect metastases even when they are extremely small (e.g. single pelvic lymph node).

Once it became possible to confidently and accurately pin-point very early distant disease, this opened another option for treating distant disease in a targeted way, rather than moving straight to systemic treatments (hormones and chemotherapy). The metastases-directed therapy used is Stereotactic Ablative Body Radiotherapy (SABR) because of the high degree of accuracy it affords.

As with all advances and changes in disease management, it has been important to measure and evaluate exactly what difference this actually makes for patients. I have just completed a study of 18 patients managed using this approach. The aim of the study was to measure: local disease control, biochemical progression-free survival (b-PFS), toxicity (side-effects and complications) and systemic therapy-free survival.

The average age of patients in the study was 68. Previous treatments for the primary prostate cancer included surgery (8 patients), surgery and salvage prostate bed radiotherapy (7 patients), radical radiotherapy (2 patients) and cryotherapy (1 patient). Twelve patients had a single metastatic site, four patients had 2 sites and 2 patients had 3 sites. Six patients were treated with a short course of androgen deprivation therapy (ADT) in addition to SABR.
All patients had a fall in PSA with a mean reduction of 75%. At a median follow-up of 14 months (range 2 – 28.5), 14 patients (78%) had good disease control and had not needed to progress to systemic treatment. Three patients with a single pelvic lymph node metastases achieved a sustained undetectable PSA level. All 8 patients who had a post-treatment PET scan showed no residual activity in the treated site. One patient experienced G2 acute bowel toxicity, otherwise there was no significant complications and side effects.

My conclusion is metastases-directed therapy using SABR for relapsed prostate cancer is a safe treatment with promising results in terms of local control, b-PFS and delaying the initiation of systemic therapies. This minimally invasive approach has the potential to improve patients’ quality of life but requires further evaluation in randomized clinical trials.