CP-222 Clinical experience of panitumumab monotherapy as treatment for metastatic colorectal cancer

Background Panitumumab is a fully human monoclonal antibody Ig G2 whose target is the epidermal growth factor receptor (EGFR). It is indicated as monotherapy to treat patients with metastatic colorectal cancer (mCRC) that show EGFR with wild-type KRAS, after failure of chemotherapy regimens containing fluoropyrimidine, oxaliplatin and/or irinotecan. Purpose The purpose of this study was to evaluate the effectiveness and safety of panitumumab monotherapy in patients with mCRC. Material and methods This was a retrospective observational study of patients with mCRC treated with panitumumab as monotherapy from June 2008 to September 2015. Demographic, clinical and pharmacotherapeutic information was collected from the computerised medical records. The main effectiveness variables were: type of response to treatment (following RECIST criteria), progression free survival (PFS) and overall survival (OS). Frequency of adverse effects and severity (according to CTCAE V.4.0) established the safety profile of the treatment. Results 30 patients were included: 73% men (n=22), average age 65.4 years (SD=10.7), 56.6% (n=17) ECOG PS 2 at the beginning of treatment and 46.7% (n=14) stage IV diagnosed. Panitumumab was used as a second-(n=10), third- (n=11) and fourth-line (n=9) treatment. Median number of cycles was 6 (IQR 4–10) and the average treatment period was 3.9 months (SD=2.6). Objective response rate was 10% (n=3), all being partial responses. 10% (n=3) showed stabilisation of disease and 63.3% (n=19) progression. In 5 patients the response was not evaluable (2 treatment cycles until death). The SLP median was 3 months (95% CI 1.7–4.2) and the SG median was 8 months (95% CI 3.6–12.3). Dermatologic toxicities occurred in 70% (n=21) of patients, and were severe (grade 3 and higher) in 15% of patients receiving panitumumab monotherapy. It was necessary to reduce the drug dose in 3 patients (due to dermal toxicity), with an average reduction of 26% (SD=11.5, range 20–40). Conclusion Panitumumab as monotherapy showed adequate effectiveness (SLP median 3 months and SG median 8 months) in patients with mCRC: pretreated, KRAS wild-type and poor performance status. It should be noted that dermal toxicity was observed in 70% of patients, characteristic of the EGFR inhibitor family. Future guidelines for mCRC treatment will have to establish the optimum sequence of use of the available therapies with the aim of achieving the greatest clinical benefit in patients. References and/or acknowledgements I want to thank Beatriz Sanchez Castellanos for her support and time. No conflict of interest