FDA Approval: Enzalutamide (Xtandi) for Prostate Cancer

First, the words in the indication

The 2012 label reads: XTANDI is an androgen receptor inhibitor indicated for the treatment of patients with metastatic castration-resistant prostate cancer who have previously received docetaxel.

Three phrases in that sentence carry the whole story, and each is worth unpacking.

Androgen receptor inhibitor. Prostate cancer cells are usually driven by male hormones, chiefly testosterone. Those hormones work by docking onto a protein inside the cell called the androgen receptor. Enzalutamide blocks that docking point.

Castration-resistant. Standard treatment for advanced prostate cancer lowers testosterone to very low levels, either with drugs or with surgery. Castration-resistant means the cancer has found a way to keep growing anyway. It does not mean hormone treatment stops; the label directs that a GnRH analog continue alongside.

Previously received docetaxel. Docetaxel is a chemotherapy drug. In 2012 this approval applied only after it.

What FDA approved, and when

FDA approved Xtandi on 31 August 2012 under NDA 203415, held by Astellas. Drugs@FDA lists it as a new molecular entity reviewed on the priority track.

The trial behind it

The label describes a randomized, placebo-controlled, multicenter phase 3 trial in 1,199 men with metastatic castration-resistant prostate cancer who had already had docetaxel. Eight hundred received enzalutamide at 160 mg once daily; 399 received placebo. Everyone stayed on androgen deprivation therapy. Everyone in the trial took the same daily amount; yours is whatever your prescription says.

That figure describes the trial. If enzalutamide is part of your treatment, take what your own prescription says and raise any changes with the team first.

Median age was 69. Ninety-one percent had cancer in bone, and 23% had it in the lung or liver.

At a pre-planned interim analysis, median overall survival was 18.4 months in the enzalutamide group against 13.6 months on placebo. The hazard ratio was 0.63.

That is a difference of about five months in the median, in a group whose alternative was placebo added to ongoing hormone treatment.

Two design details are worth noticing. Men with a history of seizure, or on medicines that lower the seizure threshold, were excluded. And the trial measured overall survival directly rather than a substitute for it, which makes the result unusually easy to interpret. Our page on clinical trial phases covers why that distinction matters.

The side effect that shaped the label

The original 2012 label had a single warnings section, and it was about seizures. Seizure occurred in 0.9% of men taking Xtandi. FDA noted there was no trial experience in men who had already had a seizure, or who had other risk factors for one.

That is a small number and a serious event, and the honest way to describe it is both at once. Roughly one man in a hundred, and a warning built into the label from day one.

Common side effects listed in 2012 included fatigue, back pain, diarrhea, joint pain, hot flushes, swelling, muscle and bone pain, headache, and weakness.

Fourteen years of label expansion

Prostate cancer drug approvals tend to move earlier in the disease over time, and this one did.

The current prescribing information covers castration-resistant prostate cancer without the docetaxel requirement, metastatic castration-sensitive prostate cancer, and non-metastatic castration-sensitive prostate cancer with biochemical recurrence at high risk of spreading.

"Biochemical recurrence" means the PSA blood test has risen after treatment, with no visible tumor on scans. Treating at that point is a genuinely different proposition from treating visible metastatic disease, and it rests on separate trials.

The warnings section has also grown, and now includes falls and fractures, high blood pressure, a heart-rhythm concern, and severe swallowing difficulty related to the size of the tablet.

Where prostate cancer stands

SEER relays an American Cancer Society projection of about 333,830 new prostate cancer diagnoses in the United States in 2026 and about 36,320 deaths. Median age at diagnosis is 68.

Sixty-nine percent of cases are found while confined to the prostate, and 14% after spread to nearby lymph nodes. For both groups the five-year relative survival figure reaches 100%. Nine percent are found after distant spread, where it is 40.1%.

That last figure is the group this 2012 approval was written for. It has moved a great deal since the trial reported, and the drugs on this page are part of the reason.

Across all stages, five-year relative survival is 98.2% for men diagnosed from 2016 through 2022. Our overview of prostate cancer explains why that headline number hides so much variation.

What this does and doesn't change

An approval sets who is eligible in general. It does not decide the order of treatments for one man, which depends on prior therapy, symptoms, where the cancer has spread, and what he is willing to live with.

Nothing here says enzalutamide is better than the alternatives now available. The 2012 comparison was against placebo, and the field has several drugs in this class today. Our page on targeted therapy covers how hormone-directed treatments differ from chemotherapy.

What to keep in perspective

• Median survival is the middle of a spread, not a per-person gain. Half the group did better and half did worse.
• The trial excluded men with seizure risk factors, so the 0.9% seizure rate describes a screened population.
• The label is not the one approved in 2012. Anyone reading about eligibility should read the current version, not this history.

If this is relevant to you, questions to ask

• Which stage of prostate cancer does this drug apply to in my case?
• What is the expected benefit compared with the other options at this point?
• What monitoring is needed, and which symptoms should I report right away?

Sources

• FDA Drugs@FDA overview: XTANDI (enzalutamide), NDA 203415
• FDA label: XTANDI, original approval 31 August 2012 (PDF)
• FDA label: XTANDI, current prescribing information (PDF)
• FDA approval letter: XTANDI, NDA 203415 (PDF)
• NCI SEER Stat Facts: Prostate Cancer

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

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