This is a gall or hypertrophy, a kind of plant tumour caused by a fungus, an insect, or even bacteria. Some can be harmful but many do the plant no real harm. Short of doing something drastic like cutting the plant off just below the gall (which I'd guess would finish off a palm!) I'd just leave it and see what happens. The chances are your plant will survive. I must admit though I've never heard of this on palms before.