Celgene (Nasdaq: CELG) is moving from cancer, where there are a lot of niches with little to no competition, to larger markets with more competition.

And that's a little scary.

So it's not a big surprise that Celgene's shares ended pretty close to flat yesterday despite presenting data that make it clear that its anti-inflammatory drug, apremilast, is working in patients with psoriatic arthritis.

Celgene didn't release much data, but what it did release sounded pretty good. The drug produced a statistically significant increase in the number of patients that had decreased their symptoms by 20%. Since that was the primary endpoint of the study, we can call it a success. The increase over placebo is especially impressive because these were patients who hadn't achieved an adequate response on other medications such as Abbott Labs' (NYSE: ABT) Humira, Pfizer (NYSE: PFE) and Amgen's (Nasdaq: AMGN) Enbrel, and Remicade, sold by Johnson & Johnson (NYSE: JNJ) and Merck (NYSE: MRK).

There are two more trials of patients with psoriatic arthritis, which is kind of like a cross between psoriasis and rheumatoid arthritis, which are expected by the end of the year. Celgene is also running trials in patients with psoriasis and another inflammatory disease called ankylosing spondylitis that affects joints between the spinal bones.

The big kahuna is rheumatoid arthritis, but at this point apremilast doesn't appear to be working in that disease. In a phase 2 trial, the drug failed to show an effect when combined with methotrexate, a standard first-line therapy. The lack of efficacy in rheumatoid arthritis is kind of weird since autoimmune diseases typically respond to the same anti-inflammatory drugs. Humira, for instance, is approved to treat six different inflammatory diseases.

There's still another phase 2 trial in rheumatoid arthritis testing apremilast as a monotherapy that should shed light on the whether the drug is effective in rheumatoid arthritis. Success there would be huge, but it would also be worrisome since Celgene has never launched a drug into such a large market with so many different players.

The rheumatoid arthritis market may be large, but Fool analysts have found a larger one. Find out what it is and how to profit from it in our free report, "The Next Trillion-Dollar Revolution." Get your free copy by clicking here.