Amgen: Vectibix disappoints in colorectal cancer but hope remains

Amgen's Vectibix has failed to meet a secondary endpoint of overall survival in patients with KRAS wild-type metastatic colorectal cancer. This is a setback as initial positive results for the drug had suggested a strong positioning against Erbitux in the first-line. However, Vectibix did show a trend towards an improvement in survival, and Amgen may now consider further trials on this basis.

Amgen's announcement relates to results from the Phase III PRIME '203' trial evaluating Vectibix (panitumumab) administered in combination with FOLFOX (leucovorin, 5-fluorouracil, oxaliplatin) as a first-line treatment for metastatic colorectal cancer (CRC). Median overall survival for Vectibix was 23.9 months compared to 19.7 months for patients treated with FOLFOX alone. Overall survival was the PRIME study's secondary endpoint and the difference of 4.2 months failed to meet statistical significance (p=0.072).

Vectibix is a recombinant, fully human IgG2 kappa monoclonal antibody that binds specifically to the human epidermal growth factor receptor (EGFR). Vectibix is approved in the US and EU as a monotherapy for the treatment of patients with EGFR-expressing metastatic CRC after disease progression on or following fluoropyrimidine, oxaliplatin and irinotecan-containing chemotherapy regimens. Currently Vectibix is in several Phase III trials investigating its use in other lines of metastatic CRC therapy, as well as metastatic head and neck cancer.

CRC is the third most common type of cancer and Datamonitor forecasts its incidence in the seven major pharmaceutical markets to be more than 478,000 in 2009. Cure is not possible for most patients with the disease, but chemotherapy with or without molecular targeted therapies may be used to improve symptoms and prolong life.

Previous PRIME study results for Vectibix presented at the European Society for Medical Oncology Congress in September 2009 were encouraging. Vectibix met its primary endpoint of increasing progression-free survival when administered in combination with FOLFOX in the PRIME study, and in the separate Phase III '181' trial, progression-free survival was improved when Vectibix was combined with FOLFIRI (leucovorin, 5-fluorouracil, irinotecan).

If approved for first-line metastatic CRC, Vectibix will be competing with Erbitux (cetuximab; Eli Lilly/Merck Serono/Bristol-Myers Squibb): another anti-EGFR monoclonal antibody. Results from the recent Phase III CRYSTAL trial evaluating Erbitux in combination with FOLFIRI (folinic acid, fluorouracil, irinotecan) demonstrated that patients in the Erbitux arm had a significantly improved overall survival (p=0.0094) compared to those receiving chemotherapy alone.

In the CRYSTAL trial, Erbitux improved median overall survival by 3.5 months. Despite not being statistically significant, Amgen will be encouraged by the median overall survival improvement of 4.2 months in the most recent PRIME trial. The company should consider further trials to further explore the drug's impact on survival and increase its chances of effectively competing with Erbitux.

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