14579 Background: Two monoclonal antibodies (mAbs) targeting the epidermal growth factor receptor are approved for the treatment (tx) of advanced mCRC - panitumumab (Vectibix™), a fully human mAb, and cetuximab (Erbitux®), a chimeric mAb. Potential for cross-reactivity between these two mAbs with regard to infusion reactions (IR) has not been fully explored. Given the lack of sequence homology between the 2 agents and the fully human nature of panitumumab, it is hypothesized that pts intolerant to cetuximab due to IR could be tolerant to panitumumab. Methods: Single pt tx IND applications to administer panitumumab monotherapy in pts with advanced mCRC were approved by the FDA and local institutions as part of the Panitumumab Compassionate Use program. Eligibility also included previous tx with standard chemotherapy and intolerability to cetuximab, ie. CTCAE v3.0 grade 3 (severe) or grade 4 (life-threatening) IR. Results: Upon informed consent, 4 pts (2M/ 2F) were enrolled in 4 centers. Median (range) age was 62.5 (52, 64) years. 3 pts had colon cancer and 1 pt had rectal cancer. All had surgery and received prior 5-fluorouracil, leucovorin, irinotecan, oxaliplatin, bevacizumab, and cetuximab. One pt had a CTC grade 3 IR and 3 pts had a CTC grade 4 IR to cetuximab. IR symptoms included fever, wheezing, dyspnea, chest/back/abdominal pain, anxiety, hypotension, flushing, tachycardia, and tachypnea. Two IRs occurred within 10 minutes of the first cetuximab infusion. Cetuximab was discontinued and IR symptoms were treated with bronchodilators, diphenhydramine, epinephrine, methylprednisolone, oxygen, intravenous saline, and hospitalization. All pts received panitumumab. Data for pts 1, 2, and 3 are available: pt 1 received 1 infusion of panitumumab at 5 mg/kg Q2W with premedication (diphenhydramine and methylprednisolone); pts 2 and 3 received 7 and 2 panitumumab infusions, respectively, at 6 mg/kg Q2W without premedication. No pt had an IR to panitumumab. Pt 2 had stable disease; pts 1 and 3 died due to disease progression. Conclusions: Panitumumab monotherapy was tolerated without incidence of an IR in these cases of mCRC pts who are intolerant to cetuximab due to a severe or life-threatening IR. Additional data will be presented. No significant financial relationships to disclose.