The addition of Vectibix® (panitumumab) to best supportive care improves survival over best standard care alone among colorectal cancer patients who have stopped responding to chemotherapy. However, the benefit is only seen with patients who have no RAS mutations, or those with only the KRAS exon 2 mutation. These results were recently presented at the 2016 Annual Gastrointestinal Cancers Symposium.
When colon cancer is diagnosed, other tests may be performed on the specimen in order to further classify the cancer and determine the optimal treatment strategy. Based on the results of these tests, treatment of colon cancer is individualized.
Vectibix is an agent that is targeted against the epidermal growth factor receptor (EGFR) pathway. The EGFR pathway is involved in cellular growth and replication, so if it is overexpressed and/or mutated, the replication of cancer cells via the pathway can remain uncontrolled.
Vectibix produces its anti-cancer effects through binding to a specific site along the EGFR pathway, which halts or decreases the cancer cell’s replication.
However, results from prior studies have revealed that EGFR inhibitors only produce anti-cancer effects if there were no mutations within the RAS gene. Further results revealed that a mutation within the region identified as exon 2 of the KRAS gene still confers sensitivity to EGFR inhibitors.
Researchers continue to evaluate different mutations and possible associated responses to EGFR inhibitors to identify patients who do not derive benefit from treatment with that class of agents.
A large clinical trial was recently conducted to compare Vectibix plus best supportive care (BSC), to BSC only among 377 patients with colorectal cancer that had stopped responding to chemotherapy. Patients’ tissue samples from their cancer were tested for specific mutations corresponding to the RAS, KRAS, and NRAS genes. Patients had not received prior therapy with EGFR inhibitors.
- The overall survival was significantly improved among patients treated with Vectibix plus BSC versus BSC only. The survival improvement, however, was only achieved in patients with no RAS mutations, or those with KRAS exon 2 mutations. Patients with other mutations did not receive benefit from treatment with Vectibix.
- Patients with no RAS mutations achieved an even greater benefit from treatment with Vectibix than those with KRAS exon 2 mutations.
- No new safety issues associated with Vectibix treatment were identified.
The researchers stated that the results of this study provide further evidence of “the importance of RAS testing at diagnosis to best inform the use of Vectibix to treat colorectal cancer.”
Patients diagnosed with colorectal cancer should speak with their physician regarding RAS testing as early as possible.
Reference: Kim T-W, Elme A, Kusic Z, et al. An open label, randomized phase III trial evaluating the treatment (tx) effects of panitumumab (pmab) + best supportive care (BSC) versus BSC in chemorefractory wild-type (WT) KRAS exon 2 metastatic colorectal cancer (mCRC) and in WT RAS mCRC. Proceedings from the 2016 Gastrointestinal Cancers Symposium. Abstract 642. Available at: https://meetinglibrary.asco.org/content/159907-173. Accessed January 26, 2016.
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