How long Xtandi (enzalutamide) keeps working depends heavily on the stage of prostate cancer being treated and how well your PSA responds in the first months. For men with metastatic castration-resistant prostate cancer, the drug typically controls disease progression for roughly one to three years. For earlier-stage disease, it can work considerably longer, with some patients showing no progression after five years of follow-up.
How Xtandi Slows Prostate Cancer
Prostate cancer cells rely on testosterone to grow. Even when standard hormone therapy has driven testosterone to very low levels, cancer cells can adapt by becoming hypersensitive to whatever small amounts remain. Xtandi works by blocking the receptor that testosterone binds to on cancer cells, preventing it from entering the cell nucleus and switching on the genes that drive tumor growth. It interrupts this process at multiple steps, making it more thorough than older anti-androgen drugs.
You take 160 mg once daily, with or without food, and continue until the cancer progresses or side effects become intolerable. Doctors typically monitor your PSA levels every few months to gauge whether the drug is still doing its job.
Duration by Stage of Disease
Metastatic Castration-Resistant Prostate Cancer
This is cancer that has spread and is growing despite standard hormone therapy. In the large PREVAIL trial, men on Xtandi delayed disease progression so substantially that researchers couldn’t even calculate a median time to progression at the point of analysis, while men on placebo progressed after just 3.9 months. After about 22 months of follow-up, Xtandi reduced the risk of death by 29% compared to placebo. Most oncologists estimate that Xtandi controls this stage of disease for a median of roughly 18 to 20 months, though individual results vary widely.
Non-Metastatic Castration-Resistant Prostate Cancer
When the cancer hasn’t yet visibly spread but PSA levels are rising despite hormone therapy, Xtandi tends to work longer. Data from the PROSPER trial shows the duration depends on how deeply your PSA drops. Men whose PSA fell by 50% to 90% had a median of about 26 months before metastasis appeared. Those with a PSA drop of 90% or more reached a median of at least 36 months, and men whose PSA fell below 0.2 ng/mL hadn’t reached a median at all, meaning more than half were still progression-free when the study ended.
In practical terms, the deeper your PSA drops in the first few months, the longer Xtandi is likely to keep working.
Metastatic Hormone-Sensitive Prostate Cancer
This is newly diagnosed metastatic cancer that still responds to standard hormone therapy. When Xtandi is added to that therapy from the start, the results are the most durable. Five-year data from the ARCHES trial showed a 66% survival rate for men on Xtandi versus 53% on placebo. For men with high-volume disease (cancer that has spread extensively), adding Xtandi extended survival by a median of 36 months compared to hormone therapy alone. At over five years of follow-up, median overall survival still hadn’t been reached in the Xtandi group, meaning most men were still alive.
High-Risk Biochemical Recurrence
Some men have no visible cancer on scans after initial treatment but their PSA is rising rapidly, signaling the cancer may return. The EMBARK trial tested Xtandi in this earlier setting and found it cut the risk of metastasis by 58% when combined with standard hormone therapy, and by 37% when used alone. For patients whose PSA becomes undetectable (below 0.2 ng/mL) after 36 weeks, treatment can be temporarily paused, a significant quality-of-life advantage since it means a break from side effects.
How You’ll Know It’s Working
PSA is the primary marker your doctor will track. A falling PSA in the first 12 to 16 weeks is a strong positive signal. The speed and depth of that decline matters: men whose PSA drops by 90% or more tend to get years of benefit, while those with less than a 50% decline often see progression much sooner. Imaging scans are typically done periodically to look for new or growing tumors, but PSA changes usually show up first.
Most patients notice the drug’s effects indirectly. Pain may decrease, energy may improve, and urinary symptoms may ease. These changes often begin within the first few weeks.
Signs the Drug Has Stopped Working
Roughly 15% to 25% of men with castration-resistant prostate cancer never respond to Xtandi in the first place, meaning their PSA doesn’t drop and tumors don’t shrink. For the 75% to 85% who do respond initially, resistance develops eventually in nearly all cases. The cancer cells find alternative pathways to grow, bypassing the receptor Xtandi is blocking.
The first sign is usually a rising PSA on two or more consecutive blood tests. Other signals include new or worsening bone pain, unexplained weight loss, increased fatigue beyond what the drug itself causes, or new findings on imaging. A rising PSA alone doesn’t always mean immediate treatment changes, but it does prompt closer monitoring and usually a conversation about next steps.
Why Some People Stop Before Progression
Not everyone stays on Xtandi until the cancer breaks through. In one analysis, side effects and disease progression each accounted for about equal shares of treatment discontinuation. Among patients who stopped within the first year (excluding those who died), side effects were the reason more than half the time, with fatigue being the most common complaint, followed by neurological symptoms like dizziness or cognitive changes. The discontinuation rate due to side effects at one year was about 11% for Xtandi specifically.
This means roughly 9 out of 10 patients who start Xtandi are still tolerating it at the one-year mark. For many, manageable side effects are a worthwhile trade for months or years of disease control. Dose reductions can sometimes help patients stay on therapy longer when side effects become bothersome but aren’t severe.
What Affects How Long It Works
Several factors influence your individual timeline. Disease volume matters: men with fewer metastases at the start tend to respond longer. PSA doubling time before starting Xtandi is another predictor, with slower doubling times linked to longer benefit. Whether you’ve had prior treatments with similar drugs (like abiraterone) also plays a role, since the cancer may have already developed partial resistance to androgen-blocking strategies.
General health, age, and the specific genetic characteristics of the tumor all factor in as well. There’s no reliable way to predict exactly how long any individual will respond, but the PSA response in the first three to four months provides the strongest early clue. A rapid, deep PSA decline is consistently associated with longer disease control across every stage of prostate cancer where Xtandi is used.