Microvesicles are small membrane vesicles that either shed or bud off eukarotic cells. Analysis of the nucleic acid content of microvesicles may be useful in detecting the presence or absence of genetic aberrations. This invention discloses novel methods of diagnosing, prognosing, monitoring, or treating a disease, such as cancer, or other medical condition in a subject involving analyzing one or more nucleic acids contained within an isolated microvesicle for the presence or absence of one or more Kras genetic aberrations.