The use of panitumumab (Pan) in patients (pts) with metastatic colorectal carcinoma (CRC) whose disease has progressed through treatment (Rx) with cetuximab (Cet)

Abstract

e15142 Background: Both Pan and Cet have activity in the Rx of metastatic CRC. As they each target the epidermal growth factor receptor, and are believed to have the same mechanism of action, pts who fail Rx with one of these agents are generally not treated with the other. Methods: A retrospective chart review was performed of pts in our practice with metastatic CRC. The response to Pan of pts whose disease had progressed despite use of a Cet containing regimen was assessed. Results: We identified three pts who received Pan after failing Rx with Cet. Pt 1 was an 81 year old female who had discontinued Rx with 5- fluorouracil (5-FU) and leucovorin (Lcv) plus bevacizumab (bev); capecitabine; and irinotecan due to intolerance. She received Cet for 6 months with initial stable disease (SD) and subsequent progressive disease (PD). She was later treated with Pan for 6 months with slight shrinkage of her metastatic disease (SD by response evaluation criteria in solid tumors) and marked improvement of her performance status (PS) before eventual PD. Pt 2 was a 43 year old female who had eventual PD after Rx with oxaliplatin and capecitabine plus bev; irinotecan plus bev; and an experimental vaccine. She was treated with Cet for 6 months with a PR, followed by PD. She received Pan for 3 months, with improvement in her PS, decreased pain and a 45% decline in her carcinoembryonic antigen level, before eventual PD (no radiologic studies were obtained during Rx with Pan). Pt 3 was a 64 year old female whose prior Rx had included oxaliplatin plus infusional 5-FU and Lcv (FOLFOX), as well as irinotecan plus infusional 5-FU and Lcv (FOLFIRI) with Cet; the latter was continued for 3.5 months, with a best response of SD. She then received 4 doses of Pan, but had PD. Conclusions: Pan led to clinical improvement with objective evidence of disease stabilization or response in 2 of 3 pts in our practice who had previously failed Cet. Pan has meaningful, although modest, activity in pts with metastatic CRC whose disease has progressed through Cet. The use of Pan should be considered in pts who have failed Cet and who do not have other viable Rx options. No significant financial relationships to disclose.