I have to agree with Night, expect to lose many rats fairly young if you are going to put girls down the moment a tumor pops up. Tumors are extremely common in unspayed females and most people opt to have them removed so that the rat may live and enjoy life a bit longer. Their lifespans are short enough, why not let them hang around a bit longer? I've seen many people who have had tumor removals done and the rats seem to bounce back VERY quickly from the surgery most of the time.