How to express dif probabilities at a chance node based on prior health states

I am trying to figure out a way to simplify my model. There are three different diagnosis (and other false diagnosis) that will lead to going to a particular treatment #1. The probability of success of treatment 1 is based on the true diagnostic state of the individual (ie patients with low grade dysplasia will have greater eradication than those with high grade or cancer). I have figured out how to do this with two different entering states using an if statement, but how would I do this with multiple different entering states, each with their own probability of success? Is is possible or should I just make a different treatment node for each of the entering states?