Prurisol is an immune modulator that affects the proteins present in psoriasis. When the human body is distressed, the immune system is weakened. As a result, certain proteins are released repeatedly, causing psoriasis. After Prurisol interacts with these proteins, the body breaks it down to abacavir.
The psoriasis market is crowded, but it is huge. A 10% share of a $10B market gives CTIX a $10B market cap just for P alone. My numbers are pretty conservative. If P does cure psoriasis, then a 50% market share is more likely.