Dr. Choudhury on the Importance of Volume Status in Metastatic Prostate Cancer

Atish D. Choudhury, MD, PhD, co-director of the Prostate Cancer Center, senior physician, Dana-Farber Cancer Institute, and instructor in medicine, Harvard Medical School, discusses the importance of volume status in prostate cancer.

Many retrospective studies have suggested that patients who received radiation to the prostate seem to live longer than those who did not. However, retrospective studies are limited due to selection bias, says Choudhury. Moreover, in the randomized HORRAD and STAMPEDE studies there didn't appear to be a survival benefit in the total patient population who received radiation. However, patients who had less than 5 bone metastases in the HORRAD study had a hazard ratio (HR) of 0.68, indicating a trend toward favorable overall survival (OS) in those with fewer bone metastases. However, the value never reached statistical significance because of its size.

In the STAMPEDE trial, which enrolled over 800 patients with low-volume disease, those who received radiation to the prostate experienced a statistically significant benefit in terms of OS, says Choudhury. The HR was about the same, at 0.68, further supporting the results of the HORRAD trial. Therefore, radiation to the prostate should be considered in patients with low-volume metastatic disease.

These studies taken in the larger context of trials that have been run to date indicate that volume status, whether high-volume or low-volume, has a huge impact on what approaches patients will benefit from. Patients who have high-volume disease have a much higher likelihood of benefitting from chemotherapy, whereas patients with low-volume disease are more likely to have a survival benefit with radiation to the prostate. Moreover, the survival benefit with abiraterone acetate (Zytiga) appears to be present in patients with low- and high-volume disease. However, the relationship between anatomic distribution of metastases and the underlying biology has yet to be clearly defined.