Increased incidence of spontaneous tumors in immunodeficient mice. Eleven to twelve member cohorts of wild type 129 strain mice, or 129 strain mice lacking RAG2 or RAG2 plus STAT1 were set aside to age and tumor incidences followed. At necropsy, mice were scored as either neoplasia-free, positive for adenomatous changes (pre-malignant neoplasia) or positive for unequivocal adenocarcinomas. These results were confirmed subsequently using larger groups [adapted from (49)].