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A Study of Mevrometostat and Enzalutamide for Men with Metastatic Castration-Sensitive Prostate Cancer Who Have Not Received Hormonal Therapy or Chemotherapy

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study involves men with metastatic castration-sensitive prostate cancer, which is a type of prostate cancer that has spread to other parts of the body but still responds to treatments that lower testosterone levels. The study will test a combination of two medications: mevrometostat, which is also known by its code name PF-06821497, and enzalutamide, which is already used to treat prostate cancer. Some participants will receive mevrometostat together with enzalutamide, while others will receive placebo together with enzalutamide. The purpose of the study is to find out if adding mevrometostat to enzalutamide can help delay the worsening of the cancer compared to using enzalutamide with placebo.

During the study, participants will take their assigned medications by mouth as tablets or capsules. They will continue their ongoing hormone therapy that lowers testosterone levels throughout the study. The study will track how long it takes for the cancer to get worse by using imaging scans, which are special pictures of the inside of the body taken with machines. The study team will also monitor various aspects of health, including blood tests to measure a substance called prostate-specific antigen, pain levels, quality of life, and any side effects that may occur. Participants will attend regular visits where doctors will perform examinations and tests to assess how the treatment is working and how participants are feeling.

The study will also look at other important measures such as how long participants live, whether tumors shrink in response to treatment, how long any tumor shrinkage lasts, and how long it takes before additional cancer treatments are needed. Doctors will carefully monitor for any unwanted effects of the medications and will check participants' overall well-being through questionnaires about pain, tiredness, and daily functioning. Blood samples will be taken at certain times to measure the levels of mevrometostat in the body and to examine genetic material from cancer cells that may be circulating in the blood.

The research process

The trial runs in 8 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Treatment initiation

    Your treatment will begin on Day 1 after completing all required tests and procedures.

    You will be randomly assigned to receive either the study medicine mevrometostat combined with enzalutamide, or a placebo combined with enzalutamide. Neither you nor your doctor will know which treatment you receive.

    You must continue your androgen deprivation therapy (a treatment that lowers male hormones) throughout the entire study. This therapy must have been started before entering the trial.

  2. Step 2

    Daily medication

    You will take enzalutamide capsules by mouth every day. The dose is 40 mg soft capsules.

    You will also take mevrometostat tablets or placebo tablets by mouth every day. These tablets are taken orally.

    You must take your medications as instructed throughout the treatment period.

    If you previously received certain hormone treatments such as estrogens, cyproterone acetate, or first-generation antiandrogens, these must be stopped before starting the trial medication.

  3. Step 3

    Regular study visits

    You will attend regular study visits at the trial site.

    During these visits, blood samples will be taken before you take your daily dose to measure the levels of the study medicine in your blood.

    Blood samples will also be taken after you take your dose at selected visits.

    Blood tests will be performed to measure your prostate-specific antigen levels, which is a marker used to monitor prostate cancer.

    Additional blood tests will be conducted to check for circulating tumor DNA, which are cancer-related genetic materials in your blood.

  4. Step 4

    Imaging scans

    You will undergo imaging scans at scheduled intervals to assess how your cancer is responding to treatment.

    These scans may include CT scans or MRI scans to check for soft tissue or organ involvement.

    You will also have bone scans to monitor any cancer spread to your bones.

    The scans will be reviewed by independent experts who do not know which treatment you are receiving.

  5. Step 5

    Safety monitoring

    Your health will be closely monitored throughout the study for any side effects or adverse reactions.

    Electrocardiograms (heart rhythm tests) will be performed at selected visits to monitor your heart function.

    Laboratory tests will be conducted regularly to check your blood counts, liver function, kidney function, and other health indicators.

    Any side effects will be assessed and graded according to standard medical criteria.

  6. Step 6

    Quality of life assessments

    You will be asked to complete questionnaires about your symptoms and quality of life at regular intervals.

    These questionnaires will ask about pain levels using the Brief Pain Inventory.

    You will complete questions about fatigue using the Brief Fatigue Inventory.

    Additional questionnaires will assess your overall well-being, daily functioning, and prostate cancer-specific symptoms.

    You will also complete a general health status questionnaire.

  7. Step 7

    Ongoing treatment period

    You will continue taking the study medications daily as long as your cancer does not progress and you do not experience unacceptable side effects.

    Your doctor will monitor for signs of disease progression through regular scans, blood tests, and physical examinations.

    The study will track the time until your cancer shows signs of progression, until it becomes resistant to hormone therapy, or until you require additional cancer treatment.

  8. Step 8

    End of treatment

    Your treatment in the study will end if your cancer progresses, if you experience unacceptable side effects, or if you decide to stop participating.

    If your disease progresses or becomes resistant to hormone therapy, your doctor will discuss other treatment options with you.

    The study team will continue to collect information about your health and survival status even after you stop taking the study medication.

Who can join the trial?

6 criteria

  • You must be a male participant who is 18 years of age or older at the time of screening
  • You must have a confirmed diagnosis of adenocarcinoma of the prostate, which is a type of cancer that starts in the gland cells of the prostate. This diagnosis must be confirmed through a tissue sample examined under a microscope. The cancer should not have small cell features, although other minor cell types are allowed if adenocarcinoma is the main type
  • You must have metastatic prostate cancer, which means the cancer has spread from the prostate to other parts of your body. This spread must be shown on imaging tests such as a bone scan showing cancer in the bones, or a CT scan or MRI scan showing cancer in soft tissues or organs
  • Any side effects from previous treatments must have improved to either your normal baseline level or to a mild level, unless your doctor determines that remaining side effects do not pose a safety risk
  • You cannot have received certain types of prostate cancer treatments before joining the study, with some exceptions. You cannot have had chemotherapy or specific hormone-blocking medications. However, you may have had androgen deprivation therapy or ADT, which is a treatment that lowers male hormone levels, for up to 3 months before joining, and you must continue this treatment during the study. You may have used certain older hormone medications until joining the study, but these must be stopped before you start. You may have had one session of radiation therapy or surgery to relieve symptoms, as long as it was completed at least 2 weeks before joining the study
  • You must have an ECOG performance status of 0 or 1, which is a measure of how well you can perform daily activities. A score of 0 means you are fully active, and a score of 1 means you have some restrictions but can still do light work

Who cannot join the trial?

3 criteria

  • Women cannot participate in this study because it is only for male patients
  • Children and teenagers cannot participate in this study as it is designed for adults
  • Patients who are part of vulnerable populations, which means groups of people who need special protection in medical research, cannot participate
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Investigated drugs

  • Mevrometostat

    is an investigational medication being studied in this trial. It is given in combination with enzalutamide to see if it can help slow down the progression of prostate cancer that has spread to other parts of the body. This medication works by blocking certain proteins that cancer cells need to grow.

  • Enzalutamide

    is a medication used to treat prostate cancer. It works by blocking the effects of male hormones like testosterone that can help prostate cancer cells grow. In this trial, it is being given to all participants, either alone or together with mevrometostat.

  • Placebo

    is an inactive substance that looks like the study medication but contains no active ingredients. Some participants will receive placebo instead of mevrometostat, along with enzalutamide, to help researchers compare the effects of the actual medication.

What is already known about the treatment

  • Mevrometostat

    Mevrometostat is an experimental medication currently being tested in clinical trials for the treatment of metastatic castration-sensitive prostate cancer, which means it is a type of prostate cancer that has spread to other parts of the body but still responds to hormone therapy. This drug is being studied in combination with enzalutamide to see if it can delay cancer progression better than enzalutamide alone. Mevrometostat works at the molecular level by blocking specific proteins that control gene activity in cancer cells, potentially slowing down or stopping the growth and spread of cancer. It is administered orally in tablet form and belongs to a class of drugs known as enzyme inhibitors that target cancer cell growth mechanisms.

  • Enzalutamide

    Enzalutamide is an approved medication used to treat prostate cancer that has spread to other parts of the body and either still responds to hormone treatment or no longer responds to it. This drug is taken by mouth as a capsule or tablet, usually once daily, and works by blocking the effects of male hormones like testosterone that fuel the growth of prostate cancer cells. At the molecular level, enzalutamide prevents testosterone from binding to its receptors on cancer cells and stops these cells from receiving the signals they need to grow and multiply. It belongs to a class of medications called androgen receptor inhibitors, which are designed to interfere with hormone-driven cancer growth.

Investigated diseases

Metastatic Castration-Sensitive Prostate Cancer – This is a type of prostate cancer that has spread beyond the prostate gland to other parts of the body, such as bones or distant lymph nodes. The term castration-sensitive means that the cancer still responds to treatments that lower testosterone levels in the body. Testosterone is a male hormone that can fuel the growth of prostate cancer cells. In this stage, the cancer cells continue to depend on male hormones to grow and multiply. As the disease progresses, cancer cells spread through the bloodstream or lymphatic system to distant sites. Over time, this type of cancer may eventually stop responding to hormone-lowering treatments and progress to a more advanced form called castration-resistant prostate cancer.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2024-519369-24-00Protocol codeC2321008Estimated enrolment1 341 patientsSponsorPfizer Inc.

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