Abstract
BACKGROUND: The promise of precision oncology can only be realized when genetic alterations are identified that can be leveraged to improve response and minimize toxicity. Identifying those alterations requires the knowledge to order the right test and to interpret the results correctly. This primer is designed to help clinicians order the appropriate testing for patients with specific malignancies and to give them an informed approach to interpretation. OBSERVATIONS: Germline DNA is usually acquired from peripheral blood, buccal swab, or saliva collection in patients with a metastatic malignancy and can provide treatment options otherwise not available. However, germline testing does not indicate alterations that arise solely in tumor tissue. Somatic testing may be performed on primary tumor, metastatic biopsy, or circulating tumor DNA when the alteration is present at the time that the tumor developed and expected to be carried through the evolution of the tumor. CONCLUSIONS: The rapid growth in technology and ability to enhance understanding of relevant tumor biology continues to improve the therapeutic landscape for individuals dealing with malignancy as does our ability to find targetable genetic alterations with the potential for meaningful clinical benefit.