Cook pasta according to package directions. Drain well, reserving 1 cup pasta cooking water.
Meanwhile, while pasta is cooking, in a saute or deep frying pan over medium heat, cook bacon, stirring occasionally, until crisp, about 8 minutes. Transfer bacon with a slotted spoon to a paper towel-lined plate; reserve drippings
Add mushrooms to the pan, and sprinkle with salt and pepper. Increase the heat to medium-high and cook, stirring occasionally, until golden, about 8 minutes. Add cabbage and leeks, and cook until they wilt and have begun to caramelize, about 5 minutes. Add cream cheese and all of the pasta water, and stir until smooth. Stir in bacon. Carefully stir in cooked pasta and heat through, about 2 minutes.