these results indicate the following : ( i ) ras oncogenes are not found in all types of human malignancies , ( ii ) significant differences in the frequency of ras mutations can be found among subtypes of neoplasms derived from the same tissue , ( iii ) in lymphoid neoplasms the nras mutation correlates with the most undifferentiated acute lymphocytic leukemia phenotype , and ( iv ) nras mutations present in only a fraction of malignant cells may result from either the selective loss or the acquisition of mutated alleles during tumor development .
C0086418
human
C0027260
nras