Results from two studies suggest that antitumor activity of Panitumumab was independent of tumor EGFr expression levels in patients with metastatic colorectal cancer who have failed standard chemotherapy.

The first study examined metastatic colorectal cancer patients with either low or negative ( less than one percent positive cells ) levels of tumor EGFr staining ( the 250 study ), while the second evaluated metastatic colorectal cancer patients with tumor EGFr levels of at least ten percent ( the 167 study ).
Both ongoing multicenter, open-label, Phase 2 trials are examining antitumor activity of Panitumumab in patients with metastatic colorectal cancer who have failed standard chemotherapy, including Oxaliplatin and Irinotecan.
Patients in both studies receive Panitumumab at 6 mg/kg every two weeks until disease progression or drug intolerability.

The primary study endpoint is objective response at week 16, which are subsequently confirmed. Secondary endpoints include; objective response rate throughout study, duration of response, progression-free survival, overall survival, and safety.

At the time of the interim analysis, the 250 study had enrolled 88 patients, with 23 evaluable for response. Thirteen percent ( 3/23 ) who received Panitumumab monotherapy had a partial response, including two patients with tumor cells negative for EGFr staining. Stable disease, a cancer that is neither decreasing nor increasing in severity, was observed in 30 percent ( 7/23 ) of patients, for a total disease control ( PR + SD ) of 43 percent. The median progression-free survival time was 13.3 weeks. The study plans to enroll 150 patients.

Study 167 had enrolled 91 patients, and 39 were evaluable for response at the time of interim analysis. At week 16, eight percent of patients ( 3/39 ) demonstrated a partial response, 21 percent ( 8/39 ) had stable disease and 49 percent ( 19/39 ) had disease progression. The median progression-free survival time was 7.6 weeks. The study plans to enroll 300 patients.

The clinical trial protocols did not require pre-medication or a loading dose for administration of Panitumumab, and the incidence of infusion reactions was low: three percent ( 3/88 ) grade 1 or 2 in the 250 study; one percent ( 1/88 ), and one percent ( 1/91 ) grade 3 ( one of which led to Panitumumab discontinuation ), in the 250 and 167 studies, respectively.
There were no grade 4 or 5 infusion reactions.
The most common reported adverse events associated with Panitumumab were skin toxicities, fatigue, abdominal pain, nausea and diarrhea. Grade 3 or 4 hypomagnesemia was observed in eight percent ( 7/88 ) and 12 percent ( 11/91 ) of patients, respectively.

Panitumumab is an investigational fully human monoclonal antibody that targets the epidermal growth factor receptor ( EGFr ), a protein that plays an important role in cancer cell signaling.
Panitumumab, an IgG2 monoclonal antibody, binds with high affinity to the EGFr.
Panitumumab was generated with XenoMouse technology, which creates a fully human monoclonal antibody that contains no murine protein.

Source: 2006 American Society of Clinical Oncology ( ASCO ) – Annual Meeting


XagenaMedicine2006