This patient has metastatic colorectal cancer, and K-ras and N-ras genotyping of the tumor biopsy sample is necessary for treatment planning. The presence of multiple lung and liver metastases is not amenable to surgical resection and, as such, is incurable. In these cases, the goal of treatment is to extend survival and palliate symptoms. The increased number of chemotherapy options that are effective against metastatic colorectal cancer has prolonged median survival for patients with incurable disease from a median survival of 6 months without chemotherapy, to 12 months with 5-fluorouracil alone, to approximately 2 years with multiagent chemotherapy. This patient will likely benefit from systemic chemotherapy; the use of multiple chemotherapy agents can be anticipated, and all agents with demonstrated activity in colorectal cancer need to be considered. One consideration in planning treatment is determining whether the epidermal growth factor receptor (EGFR) inhibitors cetuximab and panitumumab can be included in the treatment plan. Approximately 50% of colorectal cancers have a mutation in the K-ras or N-ras genes. Tumors that carry these mutations will not respond to anti-EGFR agents, and patients with these tumors are therefore not candidates for treatment with these drugs.

Dihydropyrimidine dehydrogenase (DPD) is the rate-limiting enzyme in the catabolism of 5-fluorouracil. Although assays are commercially available to measure DPD levels, these assays do not inform management and have no role in the routine treatment of patients with colorectal cancer at this time.

Patients with specific UGT1A1 polymorphisms are more prone to irinotecan toxicity. Although commercial assays are also available to detect this polymorphism, they also do not inform management and are not indicated when treating patients with colorectal cancer at this time.

Multigene array prognostic assays are commercially available but also do not guide clinical decision making and therefore are not currently part of the routine management of patients with colorectal cancer.