Sales of drugs to treat prostate cancer are set to more than double from 2011 to 2021, rising from a value of $4.1 billion to $9.1 billion over the period, according to new forecasts.

Factors that will drive near-term sales growth in seven major markets - the US, France, Germany, Italy, Spain, the UK and Japan - will include the market expansion of Johnson & Johnson/Janssen Biotech/Janssen Cilag's Zytiga (abiraterone acetate) and the uptake of Medivation/Astellas Pharma's premium-priced agent Xtandi (enzalutamide), according to the research, from Decision Resources.

Following its US and European launch in 2011, Zytiga has quickly become the treatment of choice for docetaxel-pretreated metatastatic castrate-resistant prostate cancer (mCRPC) patients, says the study. By 2015, less than two years after its launch, the drug is expected to garner major-market peak-year sales of $1.8 billion, it adds. 

Xtandi, which is an androgen receptor signalling inhibitor, is expected to compete fiercely with Zytiga for share of the lucrative mCRPC market, and prescribing decisions will be shaped by physician and patient preference as well as the costs of these novel hormonal agents, it adds.

"We expect Xtandi to emerge as the patient share leader for chemotherapy-naive mCRPC and, beginning in 2016, it will become the top-selling agent in the prostate cancer market through 2021," says Decision Resources analyst Rachel Webster, "We forecast Xtandi will garner sales of $2.2 billion by 2021," she adds.

The study findings also suggest that the launch of four novel therapies since 2010 and the anticipated introduction of Algeta/Bayer HealthCare's radium-223, Alpharadin, for symptomatic mCRPC in 2013 will make this setting an increasingly crowded and competitive landscape.

The number of men with prostate cancer who develop metastatic disease per year - most frequently following metastatic recurrence of non-metastatic disease - will decline, decreasing by 25% over the next 20 years, the study forecasts. This trend will primarily be the result of recent declines in the number of men being diagnosed with prostate cancer and the prolonged length of time it takes for the disease to metastasise, it adds.

The improved overall survival associated with new drug launches will result in the number of men living with metastatic prostate cancer exceeding half a million in 2016 in these major markets, compared to a current level of 436,000. However, the number of patients living with metastatic disease will decline in the longer term, as the decreasing number of men who develop metastatic prostate cancer outweighs both the effects of population ageing and improved survival, says Decision Resources.