Predictive factors for the treatment of metastatic colorectal cancer with panitumumab

This study investigated the effectiveness of panitumumab (Vectibix) and the predictive factors for the treatment of metastatic (spread to other parts of the body) colorectal cancer. Researchers suggested that this treatment was effective for these patients and that early tumor shrinkage and RAS mutation (permanent change) are good predictive factors of the outcomes of the treatment.

Targeted therapy such as panitumumab is used alone or in combination with chemotherapy to treat patients with RAS-negative colorectal cancer. It works by blocking the tumor getting growth signals. RAS is an abnormal gene present in more aggressive types of cancer and can predict poorer outcomes. BRAF is another gene that when is abnormal sends growing signals to tumors.

Prior studies showed that panitumumab and best supportive care improved the outcomes of patients with RAS-negative colorectal cancer. However, other predictive factors are necessary to predict outcomes in these patients to give them the best possible treatment.

This study included information about 270 patients with RAS-negative advanced colorectal cancer. Patients were randomized to receive best supportive care (BSC) with (142 patients) and without (128 patients) panitumumab by injection, on day 1 of each 14-day cycle. Factors such as abnormal genes, early tumor shrinkage, and tumor response were measured. Survival outcomes were also evaluated.

Patients who received the combined treatment had 28% improvement in the odds of a better overall survival compared to BSC alone. They also had a 55% higher chance of a better progression-free survival (time from treatment to progression).

Patients with RAS and BRAF-negative tumors had a 25% improvement in the odds of a better overall survival and 55% of a better progression-free survival.

The average tumor response for the group treated with the combined treatment was 16.9%. 69.5% of the patients had any type of tumor shrinkage at week 8. 38.2% of the patients had a tumor shrinkage of 20% or more. These patients had a 42% higher chance of a better survival compared to those with shrinkage lower than 20%.?

This study confirms that panitumumab is effective for the treatment of advanced colorectal cancer. The authors also determined that RAS and early tumor shrinkage are useful predictors of patients outcomes after treatment with panitumumab.

The treatment groups were not randomized. This might have influenced the results.