Panitumumab (Vectibix) compared to cetuximab (Erbitux) in patients who do not respond to chemotherapy

This study assessed whether panitumumab is as good as cetuximab for patients with colorectal cancer that is unresponsive to chemotherapy (chemotherapy-refractory colorectal cancer).

Colorectal cancer is the fourth-leading cause of cancer related death worldwide. For patients whose cancer has metastasized (spread outside the bowel) chemotherapy is the best treatment. However, there are increasing numbers of patients who do not respond to chemotherapy. Cetuximab, a new type of anti-cancer drug can improve the survival time of these patients.

Cetuximab is a drug that binds to the epidermal growth factor receptor (EGFR) protein. As EGRF is involved in cancer growth and spread, cetuximab helps slow the cancer. The benefits of cetuximab are only seen in patients with normal-KRAS gene (wild-type KRAS).  Panitumumab also attaches to the EGFR and may offer similar survival improvements as cetuximab.

This study included 999 patients from 27 different countries. 499 patients received panitumumab and 500 patients received cetuximab. All patients had chemotherapy-refractory metastatic colorectal cancer (colorectal cancer that has spread to other organs and does not respond to chemotherapy) and a normal KRAS gene.

Patients receiving panitumumab survived as long as patients receiving cetuximab. Survival time was 10.4 months for panitumumab and 10.0 months for cetuximab.

There were a similar number of adverse events for patients receiving panitumumab as for patients receiving cetuximab. The most common moderate-to-severe adverse events for both drugs were: rash (4-5%), skin toxicity (10-13%), low blood magnesium levels (2-5%) and low blood potassium levels (2-3%). In each case more patients receiving panitumumab suffered from the adverse event. 

The authors concluded that the average survival time is similar for patients receiving panitumumab and cetuximab. Similar numbers and types of adverse effects occurred with both treatments.

This study was funded by Amgen. Amgen also manufacture and market panitumumab.