Study to Demonstrate the Efficacy (Including Inhibition of Structural Damage), Safety and Tolerability up to 2 Years of Secukinumab in Active Psoriatic Arthritis

This multicenter study uses a randomized, double-blind, placebo-controlled, parallel-group design. A screening period (SCR) running up to 10 weeks before randomization will be used to assess subject eligibility followed by 104 weeks of treatment. At BSL approximately 990 subjects whose eligibility is confirmed will be randomized to one of four treatment groups in 2:2:2:3 ratio: * Group 1 - secukinumab 150 mg s.c. without loading regimen * Group 2 - secukinumab 150 mg s.c. with loading dose regimen * Group 3 - secukinumab 300 mg s.c. with loading dose regimen * Group 4 - Placebo s.c. NOTE: Group 4 is split into 2 treatment arms, detailed description below. At randomization, subjects will be stratified on the basis of previous anti-TNF therapy as TNFα inhibitor naïve (TNF-naïve) or TNFα inhibitor inadequate responders (TNF-IR). At each study treatment visit, one (for secukinumab 150 mg) or two (for secukinumab 300 mg) s.c. injections in the form of PFS will be administered, since secukinumab is available in 1.0 mL (150 mg) PFSs. Placebo to secukinumab is also available in 1.0 mL to match the active drug. At Week 16, subjects who have been randomized to secukinumab groups at BSL (Groups 1-3) will be classified as either responders (≥20% improvement from BSL in both tender joint count (TJC) and swollen joint counts (SJC)) or non-responders (\<20% improvement from BSL TJC or SJC), however they will continue on the same treatment irrespective of their response status. At Week 16, subjects who have been randomized to placebo at BSL (Group 4) will be classified as either responders (≥20% improvement from BSL in both TJC and SJC) or non-responders (\<20% improvement from BSL TJC or SJC): * Subjects who are non-responders will receive either secukinumab 150 mg or 300 mg s.c. every 4 weeks starting at Week 16 (as dictated by treatment sequence assigned to these subjects at BSL). * Subjects who are responders will continue to receive placebo every 4 weeks. Starting Week 24, these subjects will receive either secukinumab 150 mg s.c. or 300 mg s.c. every 4 weeks starting at Week 24 (as dictated by treatment sequence assigned to these subjects at BSL). At Week 24, the assessments to address the primary objective will be performed. As described above, subjects who are still receiving placebo s.c. injection will receive either secukinumab 150 mg s.c. or 300 mg s.c. every 4 weeks starting at Week 24 (as dictated by treatment sequence assigned to these subjects at BSL). At week 52, based on Investigator's decision, the subjects on a 150 mg dose whose signs and symptoms do not show satisfactory response have the possibility to be allocated to secukinumab 300 mg s.c. After the Week 52 database lock and analyses have been completed, site personnel and subjects will be unblinded to the original randomized treatment (sequence) assignment at randomization. In addition, treatment will be given open-label in order to eliminate the placebo injection. The subject will continue to receive the same active dose of secukinumab as open-label treatment administered until Week 100.