I have done it - with a queen size jelly roll quilt. I folded it in fourths and safety pinned it around the edges. Then I washed it on the gentle cycle with cold water and a little laundry detergent. It came out ok.
Unpinned it and put it in the dryer to dry.
Luckily, I had no problems with it, but now I wonder exactly what I was thinking! It was early in my quilting experience, so I can only explain it as ignorance! I don't recommend it to anyone!