NF1 and neoplasm: MPNSTs and glioblastomas appear in the nf1/p53 background after 30 weeks of age, while melanomas develop starting at 5 weeks of age in the nf1/pten/p53 background and grow so rapidly that fish usually need to be sacrificed for humane reasons before 30 weeks of age, so melanomas are the only tumor-type observed in the nf1/pten/p53 background.