Our Molly has been getting these over the last few years. The vet has removed a couple and said they were harmlessly benign. It hadn't occurred to us that there may be ways of reducing the chance of Molly getting more, the vet has not discussed this, but if anybody has suggestions, we would be interested also.
Curiously, her "twin" brother Murphy does not get them to the same extent and they've had an identical diet since Gotcha Day; supplemented by whatever horrors Molly can find when we're out.