Randomized phase II trial of preoperative chemoradiotherapy with or without cetuximab in locally advanced rectal adenocarcinoma.

537 Background: Treatment for locally advanced rectal cancer (LARC) includes preoperative radiation concurrent with fluoropyrimidine chemotherapy (CRT). Local recurrence is a problem. Cetuximab is active in colorectal cancer and is effective with radiotherapy in other diseases. This study evaluated the pathologic response rate for LARC treated with preoperative chemoradiotherapy w/wo cetuximab. Methods: LARC (T3/4 or LN+, M0) pts were randomized to Arm1/Arm2. Arm 1 received standard pelvic radiotherapy (5040-5400cGy in daily fractions) with continuous infusional 5-FU (225mg/m 2 /day); Arm 2 received identical chemoradiotherapy + concurrent cetuximab (400mg/m 2 initial dose) 1 week before pelvic radiotherapy, followed by 250mg/m 2 weekly for the duration of chemoradiotherapy. After study treatment completion, pts were re-evaluated clinically and radiographically for clinical response. After 6-8 weeks, patients underwent surgical resection. The primary end point was pathologic CR (pCR), and secondary endpoints included ORR, RFS, OS, and local recurrence rates. Results: 139 pts were enrolled (Arm 1=69/Arm2=70); Arm1/Arm2 median age 61/55 yrs, and stage II and III 59%, 39%/40%, 60%. In 124 postsurgery pts, pCR occurred in 17 Arm 1 pts (28.3%, 95% CI 17.5-41.4) and 17 Arm 2 pts (26.6%, 95% CI 16.3-39.1); TRG postsurgery was similar between treatment arms (Table). Grade 3 and 4 toxicities were largely nonhematologic: diarrhea 16%/22%, rash 0%/12%, dehydration 5%/8%, mucositis 5%/6%. The 5-yr RFS for Arm1/Arm2 was 61%/65%, 5-yr OS was 66%/83%, local recurrence was 3%/4%. Conclusions: The addition of cetuximab to preoperative CRT for LARC was associated with increased but manageable toxicities. pCR rates were similar between treatment arms, as were survival statistics and local recurrence rates. No association was found between KRAS status and pCR. Clinical trial information: NCT00527111. [Table: see text]