After a long delay, Centocor Ortho Biotech's psoriasis drug Stelara has been approved by the U.S. Food and Drug Administration. Stelara is intended to treat moderate to severe plaque psoriasis, a skin condition that affects about 7.5 million Americans. Stelara was initially delayed in December, when the FDA asked Centocor for a risk evaluation and mitigation strategy. The drug can reduce the immune system's ability to fight infections, and patients may also run an increased risk of developing cancer. The FDA extended the approval process by three months in May, although it didn't request more data. More than 2,200 patients have been involved in clinical studies of Stelara to date. In a press release, Centocor reported that about 70 percent of patients taking Stelara achieved 75 percent skin clearance after two doses, and maintained those results for a year with continued treatment. Stelara is a monoclonal antibody that targets two proteins involved in the development of psoriasis. It is administered by injection: Patients get an initial shot, another shot four weeks later, and another shot every 12 weeks. Psoriasis is a chronic skin condition characterized by painful, inflamed red lesions. Stelara faces challenges from Amgen's Enbrel and Abbott Laboratories' Humira. Other competitors include Lerner Medical, Hermal, Incyte Corp. , Targeted Molecules Corp., and Hill Dermaceuticals.