TumorsTumor Neoplasm, new growth. Is predicated upon autonomous growth of cells or tissues into benign or malignant tumors. that are not induced, but that occur as a result of aging or some other natural defect. The frequency and incidence of spontaneous tumorsSpontaneous tumors Tumors that are not induced, but that occur as a result of aging or some other natural defect. The frequency and incidence of spontaneous tumors and the tumor type are both species- and strain-specific. and the tumorTumor Neoplasm, new growth. Is predicated upon autonomous growth of cells or tissues into benign or malignant tumors. type are both species- and strain-specific.