categorical predictor variable with many categories

I want to test the ability of a categorical variable, which has many categories, to predict the outcome of a continuous variable. Specifically, I want to see if diagnostic category (10 different diagnoses) predicts a treatment outcome. After wading through many different sites and texts, I'm still at a loss for how to set this test up in SPSS. Any help is much appreciated.

You could use dummay variables and do panel regression (see Gujarat and Porter - several editions including 2014 I think, but maybe 2013).