Most recently, expression of caudal-type homeobox transcription factor 2 (CDX2) has been reported as a novel prognostic and predictive tool. A 2015 report linked lack of expression of CDX2 to worse outcome; in this study, 5-year DFS was 41% in patients with CDX2-negative tumors versus 74% in the CDX2-positive tumors, with a HR of disease recurrence of 2.73 for CDX2-negative tumors.63 Similar numbers were observed in patients with stage II disease, with 5-year OS of 40% in patients with CDX2-negative tumors versus 70% in those with CDX2-positive tumors. Treatment of CDX2-negative patients with adjuvant chemotherapy improved outcomes: 5-year DFS in the stage II subgroup was 91% with chemotherapy versus 56% without, and in the stage III subgroup, 74% with chemotherapy versus 37% without. The authors concluded that patients with stage II and III colon cancer that is CDX2-negative may benefit from adjuvant chemotherapy. Importantly, CDX2-negativity is a rare event, occurring in only 6.9% of evaluable tumors.
RISK ASSESSMENT TOOLS
Several risk assessment tools have been developed in an attempt to aid clinical decision making regarding adjuvant chemotherapy for patients with stage II colon cancer. The Oncotype DX Colon Assay analyses a 12-gene signature in the pathologic sample and was developed with the goal to improve prognostication and aid in treatment decision making. The test utilizes reverse transcription-PCR on RNA extracted from the tumor.64 After evaluating 12 genes, a recurrence score is generated that predicts the risk of disease recurrence. This score was validated using data from 3 large clinical trials.65–67 Unlike the Oncotype Dx score used in breast cancer, the test in colon cancer has not been found to predict the benefit from chemotherapy and has not been incorporated widely into clinical practice.
Adjuvant! Online (available at www.adjuvantonline.com) is a web-based tool that combines clinical and histological features to estimate outcome. Calculations are based on US SEER tumor registry-reported outcomes.68 A second web-based tool, Numeracy (available at www.mayoclinic.com/calcs), was developed by the Mayo Clinic using pooled data from 7 randomized clinical trials including 3341 patients.68 Both tools seek to predict absolute benefit for patients treated with fluorouracil, though data suggests Adjuvant! Online may be more reliable in its predictive ability.69 Adjuvant! Online has also been validated in an Asian population70 and patients older than 70 years.71
MUTATIONAL ANALYSIS
Multiple mutations in proto-oncogenes have been found in colon cancer cells. One such proto-oncogene is BRAF, which encodes a serine-threonine kinase in the rapidly accelerated fibrosarcoma (RAF). Mutations in BRAF have been found in 5% to 10% of colon cancers and are associated with right-sided tumors.72 As a prognostic marker, some studies have associated BRAF mutations with worse prognosis, including shorter time to relapse and shorter OS.73,74 Two other proto-oncogenes are Kristen rat sarcoma viral oncogene homolog (KRAS) and neuroblastoma rat sarcoma viral oncogene homolog (NRAS), both of which encode proteins downstream of epidermal growth factor receptor (EGFR). KRAS and NRAS mutations have been shown to be predictive in the metastatic setting where they predict resistance to the EGFR inhibitors cetuximab and panitumumab.75,76 The effect of KRAS and NRAS mutations on outcome in stage II and III colon cancer is uncertain. Some studies suggest worse outcome in KRAS-mutated cancers,77 while others failed to demonstrate this finding.73
CASE PRESENTATION 1
A 53-year-old man with no past medical history presents to the emergency department with early satiety and generalized abdominal pain. Laboratory evaluation shows a microcytic anemia with normal white blood cell count, platelet count, renal function, and liver function tests. Computed tomography (CT) scan of the abdomen and pelvis show a 4-cm mass in the transverse colon without obstruction and without abnormality in the liver. CT scan of the chest does not demonstrate pathologic lymphadenopathy or other findings. He undergoes robotic laparoscopic transverse colon resection and appendectomy. Pathology confirms a 3.5-cm focus of adenocarcinoma of the colon with invasion through the muscularis propria and 5 of 27 regional lymph nodes positive for adenocarcinoma and uninvolved proximal, distal, and radial margins. He is given a stage of IIIB pT3 pN2a M0 and referred to medical oncology for further management, where 6 months of adjuvant FOLFOX chemotherapy is recommended.