X0101 EFFECT 33 LIVE 2012-10-05 0001144204-12-053362 485APOS 0001469192 MAINSTAY FUNDS TRUST 333-160918 S000038282 MainStay Marketfield Fund C000118167 Class I S000038282 MainStay Marketfield Fund C000120997 Class A S000038282 MainStay Marketfield Fund C000120998 Class C S000038282 MainStay Marketfield Fund C000120999 Class R2 S000038282 MainStay Marketfield Fund C000121000 Investor Class