Recent discoveries promise increasingly to help oncologists individually tailor anticancer therapy to their patients' molecular tumor characteristics. One such promising molecular diagnostic is Kirsten ras (KRAS) tumor mutation testing for metastatic colorectal cancer (mCRC) patients. In the current study, we examined how and why physicians adopt KRAS testing and how they subsequently utilize the information when discussing treatment strategies with patients. We conducted 34 semi-structured in-person or telephone interviews with oncologists from seven different health plans. Each interview was audiotaped, transcribed, and coded using qualitative research methods. Information and salient themes relating to the research questions were summarized for each interview. All of the oncologists in this study reported using the KRAS test at the time of the interview. Most appeared to have adopted the test rapidly, within 6 months of the publication of National Clinical Guidelines. Oncologists chose to administer the test at various time points, although the majority ordered the test at the time their patient was diagnosed with mCRC. While oncologists expressed a range of opinions about the KRAS test, there was a general consensus that the test was useful and provided benefits to mCRC patients. The rapid adoption and enthusiasm for KRAS suggests that these types of tests may be filling an important informational need for oncologists when making treatment decisions. Future research should focus on the informational needs of patients around this test and whether patients feel informed or confident with their physicians' use of these tests to determine treatment access. While oncologists expressed a range of opinions about the KRAS test, there was a general consensus that the test was useful and provided benefits to mCRC patients. The rapid adoption of KRAS suggests that this and other molecular diagnostic tests may be filling an important informational need for oncologists when making treatment decisions.