Johnson & Johnson’s experimental drug, ustekinumab appears to be effective in treating psoriasis, but its long-term use could slightly increase cancer risks, the U.S. Food and Drug Administration wrote in an analysis released on Friday, a few days before an advisory panel would discuss the drug’s efficacy and dosing.

Centocor Inc., a unit of Johnson & Johnson, is seeking approval for the drug to treat adults with chronic moderate to severe plaque psoriasis.

Psoriasis, a skin disorder that causes scaly red patches, affects an estimated 7.5 million Americans.

Ustekinumab injections work by blocking an inflammation-causing protein called tumor necrosis factor (TNF). Animal studies showed suppression of these proteins raised the chances of developing cancer, the FDA reviewer said.

An advisory panel is scheduled to discuss on Tuesday ustekinumab’s potential dangers that may arise in people taking the drug without medical supervision. Also the FDA will ask the panel whether or not to put animal data (highlighting the cancer risk) on the label of the drug or whether the company should do more research on the safety issue.

If approved, ustekinumab would compete fierce competition from other leading injectable drugs like Amgen Inc and Wyeth’s Enbrel and Abbott Laboratories Inc.’ Humira, as well as Johnson & Johnson’s Remicade, administered by intravenous infusion.

The FDA is expected to make its decision on whether to approve ustekinumab for sales in the U.S. in September.