DOI: 10.25934/pr00009387
title: Causal Mediation Role of Early prostate-specific antigen (PSA) response and pain in patients with metastatic hormone sensitive prostate cancer

description: Prostate cancer is the most common cancer in the North American male population. In 2023, the American Cancer Society estimates about 288,300 new cases of prostate cancer and about 34,700 deaths from prostate cancer. Of note, it is the second leading cause of cancer death in men in the U.S. after lung cancer. Approximately 3/4th of these patients are diagnosed when the prostate is still localized to the prostate gland. Majority of them receive curative local therapy including removal of the prostate or radiotherapy to the prostate. This is often combined with testosterone suppression as testosterone acts like a fuel for the prostate cancer cells and thus suppressing the testosterone inhibits growth of the cancer.

Despite these treatments, some of them progress to a phase where the cancer spreads to organs outside prostate. Additionally, about 1/4th of patients are diagnosed when the cancer has already spread to other organs. As long as the cancer is responsive to testosterone suppression (lowering testosterone levels), metastatic prostate cancer patients are treated with testosterone suppression in combination with other drugs such as docetaxel which is a chemotherapy agent (a type or mixture of drugs that work by killing cancer cells), novel hormonal agents (drugs that work to slow or stop cancer growth by effecting hormone levels), or both.

Novel hormonal agents are first line treatment for these patients with metastatic hormone sensitive prostate cancer (mHSPC) after they were found to be the effective in a succession of randomized controlled trials which are a type of scientific experiment where people are randomly assigned to either a treatment group or a control group that doesn't receive the treatment. Darolutamide, a hormonal agent, when added to testosterone suppression and docetaxel, a chemotherapy drug, was found to improve overall longevity in such a randomized controlled trial, known as ARASENS study.
Prostate specific antigen is a marker for prostate cancer and increase or decrease in this marker, as detected by serial blood tests, corroborate with disease progression or regression in men with prostate cancer. However, it remains unknown if early PSA response plays a causal mediation role in the treatment effect on overall longevity. Similarly, longitudinal change in pain, as reported by patients, has been reported to be associated with outcome in metastatic prostate cancer. However, it remains unknown if pain progression could also play a causal mediating role in the treatment effect on overall longevity.

We propose a secondary analysis of ARASENS trial to determine if early PSA drop and early pain progression (as defined in the trial) had any causal mediation role on the treatment effect from darolutamide in conjunction with testosterone suppression and docetaxel on overall survival (OS). In other words, we would like to determine if PSA drop and pain progression could be some of the pivotal factors through which the combination of darolutamide, testosterone suppression, and docetaxel exerts its effect on OS. If found to be mediators, this will help us determine the possible outcome of patients early in the disease course and thereafter personalize their treatment accordingly.