Evaluating the effectiveness and safety of maintenance therapy with panitumumab plus FOLFIRI in patients with RAS wild-type metastatic colorectal cancer.

This study evaluated the effectiveness and safety of panitumumab (Vectibix) rechallenge when added to maintenance therapy with FOLFIRI {fluorouracil (FU; Adrucil), folinic acid (FA; Leucovorin), irinotecan (Camptosar)} in patients with RAS wild-type metastatic colorectal cancer (mCRC). The data showed that maintenance therapy with panitumumab plus FOLFIRI was effective with manageable side effects in these patients.

Patients who are diagnosed with mCRC have disease that has spread to other areas. Genetic changes in KRAS protein can often occur to promote mCRC growth and spread. mCRC tumors that do not have these genetic changes are known as KRAS wild-type mCRC. The standard treatment for these patients is chemotherapy combined with targeted therapy.

A combination of fluorouracil and folinic acid (FU/FA) plus either oxaliplatin (Eloxatin) (FOLFOX) or irinotecan (Camptosar) (FOLFIRI) chemotherapies are the recommended first-line therapies for advanced CRC. Panitumumab is a type of targeted therapy. It works by targeting certain proteins (EGFR) on the cancer cells and stops them from growing. Chemotherapy with panitumumab has been shown to improve survival in patients with mCRC.

Maintenance treatment is commonly used after first-line treatment to delay relapse or slow down cancer progression. However, the effectiveness and safety of panitumumab rechallenge when added to maintenance therapy with FOLFIRI after progression with first-line panitumumab plus FOLFOX in patients with RAS wild-type mCRC are still unknown.

This study involved 31 patients with mCRC with cancer progression after first-line panitumumab-FOLFOX. Patients were randomly assigned into two groups. Group 1 included 18 patients who received maintenance therapy with FOLFIRI plus panitumumab. Group 2 included 13 patients who received maintenance therapy with FOLFIRI alone. The average follow-up time was 9.5 months for group 1 and 7 months for group 2.

The average survival without cancer progression was 11 months in group 1 compared to 4 months in group 2. Patients in group 1 were 42% more likely to survive without cancer progression than patients in group 2. After 6 months, 66.7% of the patients in group 1 were alive without cancer progression compared to 38.5% of the patients in group 2.

The average overall survival was 13 months in group 1 compared to 10 months in group 2. Patients in group 1 were 45% more likely to have a better overall survival than patients in group 2.

The overall response rate (ORR; partial or complete disappearance of cancer) was 33% for group 1 compared to 7.7% for group 2.

44.4% of the patients in group 1 experienced serious side effects compared to 23.1% of the patients in group 2.  

This study concluded that maintenance therapy with panitumumab plus FOLFIRI was effective with manageable side effects after progression with first-line panitumumab plus FOLFOX in patients with RAS wild-type mCRC.

This study was funded by Amgen Inc., the manufacturer of panitumumab. The sample size was very small. Larger and longer-term studies are needed to validate these conclusions.