SABR as a treatment for early metastatic prostate cancer: towards control and management

Dr Dan Ford

By Dr Dan Ford, consultant oncologist, BPC

When I speak to patients about early metastatic prostate cancer, I often describe it as being like a chronic disease. This is helpful because people understand a chronic disease (for example, diabetes and arthritis) will rarely be cured but can be managed and controlled, to a large extent. Chronic disease is a less frightening concept for the patient than what traditionally comes to mind with metastatic cancer. And for men with early metastatic (oligometastatic) cancer, it is a more accurate concept: our ability to manage and control early metastatic disease is rapidly improving.

For the past two years, I’ve been involved in developing SABR (stereotactic ablative body radiation) for patients including those with oligometastatic prostate cancer. We are currently gathering data on these patients nationally to better define the potential long term benefits for patients. Generally, these are men who have had primary prostate cancer treatment, but subsequently their PSA is rising, indicating cancer has not been fully cleared. Here, the improvements in PET (Positron Emission Tomography) technology have been game changing. This technology enables us to detect tiny metastases that would often not be visible on traditional imaging. We have two commonly used ‘tracers’ (choline and gallium-68-PSMA) which light up cell changes and allow us to visualise areas of early prostate cancer relapse.

Once we have this new level of information from imaging, we can potentially treat these areas with SABR. It was initially pioneered in treatment of tumours of the brain and early lung cancer. SABR is now being used more widely to other disease sites and tumour types. It uses standard photon radiotherapy but due to developments in treatment delivery techniques allows for a high dose of radiation to be delivered to the area of disease because harm to normal tissue is minimised.

For the man with early metastatic prostate cancer, what does this treatment option offer? Although this is unlikely to be a curative treatment, the aim is to control the disease for a significant amount of time. Importantly, we know this SABR is well tolerated by patients and potentially may be repeated in individuals if further lesions are identified.

Without this new pathway of PET scan and SABR, the standard option for men with metastatic prostate cancer after primary treatment is hormone treatment (lowering the levels of testosterone). We know many men find the side-effects of hormone treatment distressing; opening another control and management window before hormone treatment is very important from a quality of life perspective.

There are currently 17 UK centres commissioned by the NHS to collect data on these novel SABR techniques. The Queen Elizabeth Hospital in Birmingham, my NHS hospital where I am Clinical Service Lead for oncology, has recruited and treated more patients than any other centre as part of this initiative.  A number of different cancer types other than prostate cancer have been treated as well as a range of different anatomical locations of disease including lymph nodes, spine, liver and previously irradiated areas.

The results of initiative will tell us more about how best to use this new treatment pathway and understand more precisely which patients will benefit. However, it is already clear that the exciting combination of advancements in PET scanning and the utility of SABR opens a very promising new horizon for the management and control of metastatic prostate cancer.