title: The role of targeted agents in preoperative chemoradiation for rectal cancer.
abstract: In the United States, randomized trials have established preoperative chemoradiation as the standard of care for patients with locally advanced rectal cancer. Pathologic complete response (pCR) rates occur in 10% to 16% of patients and have been shown to be correlated with both disease-free and overall survival. Therefore, recent efforts incorporating newer cytotoxic and molecularly targeted agents into chemoradiotherapy regimens have reported the pCR rate to be a surrogate marker of clinical outcomes. Substitution of oral fluoropyrimidines, including capecitabine, for infusional 5-fluorouracil reportedly generated pCR rates of up to 32% in phase 2 studies, but definitive evaluation awaits results from the National Surgical Adjuvant Breast and Bowel Project (NSABP) R-04 trial. Similarly, regimens incorporating irinotecan generated pCR rates as high as 38%, but to the authors' knowledge have not been evaluated in randomized trials. In contrast, 2 large randomized trials reported that the addition of weekly oxaliplatin to fluoropyrimidine-based chemoradiation led to an increase in grade 3/4 toxicity but no difference in pCR rates. Early phase trials evaluating the anti-epidermal growth factor receptor (EGFR) antibody cetuximab in combination with chemoradiation reported modest pCR rates of 5% to 12%, and efforts have focused on identifying biomarkers of response including EGFR copy number, k-ras mutational status, and both serum and tumor-specific expression of EGFR ligands. Finally, incorporation of the anti-vascular endothelial growth factor antibody bevacizumab into chemoradiation appears to be safe and feasible, with initial studies reporting a beneficial effect on vascular normalization and correlations between circulating biomarkers of angiogenesis and pathologic response. Future efforts should include prospective studies of these agents in biomarker-defined subpopulations, as well as studies of novel agents that target angiogenesis, tumor-stromal interaction, and the cell signaling pathways implicated in colorectal cancer.
authors.affiliation: Division of Hematology/Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts 02114, USA.
authors.forename: Raymond C
authors.initials: RC
authors.lastname: Wadlow
authors.forename: David P
authors.initials: DP
authors.lastname: Ryan
mesh_terms: D000970:Antineoplastic Agents / Q000627:therapeutic use*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D002986:Clinical Trials as Topic; D016503:Drug Delivery Systems; D066246:ErbB Receptors / Q000037:antagonists & inhibitors; D006801:Humans; D012004:Rectal Neoplasms / Q000188:drug therapy* / Q000532:radiotherapy*; D042461:Vascular Endothelial Growth Factor A / Q000037:antagonists & inhibitors
chemical_list: D000970:Antineoplastic Agents; D042461:Vascular Endothelial Growth Factor A; D066246:ErbB Receptors