OBJECTIVES: To describe treatment patterns and cost in patients with PSO (psoriasis) receiving biologic therapies (BT). METHODS: A retrospective cohort of medication claims data from IMS Brogan Private (Canadian national) and Public (Ontario and Quebec) Drug Plan databases was analysed. Biologic-naïve PSO patients >18 years of age were selected between 01/01/2007 and 03/30/2011 and followed for 24 months to understand lines of therapy, retention on BT, and annual therapy costs. Target biologics included adalimumab, etanercept, infliximab and ustekinumab. RESULTS: 3,546 patients were identified. Of those, 44% initiated etanercept, 26% adalimumab, 19% ustekinumab, and 10% infliximab. 32% of patients remained on 1st line therapy, 16% switched, and 52% stopped therapy over the 24 month period. Median days on 1st line therapy was longer in public than private plans (502 vs. 357). Of those who switched, 556 received 2 lines, and 105 received 3 or more lines of BT. In a retention model of private plan patients, those who supplemented with non-biologic PSO therapies were 16% - 42% more likely to stay on BT than those taking BT alone (P<0.001); patients receiving non-PSO concomitant medications were 19% - 32% more likely to stay on their BT (p<0.001) than those not receiving; and patients who switched BT were 2.35x more likely to stop BT within 24 months versus non-switchers (p<0.001). Using a cost model, patients who switched BT had higher average annual costs of $4,355 and $3,679 in private and public plans respectively compared to those who didn’t switch (P<0.001). CONCLUSIONS: 68% of PSO patients on BT either switch or stop therapy, indicating there remains an unmet need for new treatment options. In addition, switching is associated with significantly higher therapy costs. With better understanding of predictors for retention, patient support programs can be designed to address the specific needs of at-risk groups.