Panitumumab as a radiosensitizing agent in KRAS wild-type locally advanced rectal cancer

Our goal was to optimize the radiosensitizing potential of anti-epidermal growth factor receptor (EGFR) monoclonal antibodies, when given concomitantly with preoperative radiotherapy in KRAS wild-type locally advanced rectal cancer (LARC). Based on pre-clinical studies conducted by our group, we designed a phase II trial in which panitumumab (6 mg/kg/q2 weeks) was combined with preoperative radiotherapy (45 Gy in 25 fractions) to treat cT3-4/N + KRAS wild-type LARC. The primary endpoint was complete pathologic response (pCR) (H0 = 5 %, H1 = 17 %, α = 0.05, β = 0.2). From 19 enrolled patients, 17 (89 %) were evaluable for pathology assessment. Although no pCR was observed, seven patients (41 %) had grade 3 Dworak pathological tumor regression. The regimen was safe and was associated with 95 % of sphincter-preservation rate. No NRAS, BRAF, or PI3KCA mutation was found in this study, but one patient (5 %) showed loss of PTEN expression. The quantification of plasma EGFR ligands during treatment showed significant upregulation of plasma TGF-α and EGF following panitumumab administration (p