What is the role of panitumumab in the treatment of colon cancer?

Updated: Apr 15, 2020
  • Author: Tomislav Dragovich, MD, PhD; Chief Editor: N Joseph Espat, MD, MS, FACS  more...
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Answer

Panitumumab is a fully human monoclonal antibody against EGFR. This agent was originally approved as monotherapy for patients with EGFR-expressing metastatic colorectal cancer in whom combination chemotherapy with regimens containing fluoropyrimidine, oxaliplatin, and irinotecan had failed or was not tolerated.

In May 2014, the FDA approved panitumumab for first-line treatment of patients with wild-type KRAS (exon 2) metastatic colorectal carcinoma in combination with fluorouracil, leucovorin, and oxaliplatin (FOLFOX4). [112] Approval was based on results from the PRIME trial. [113]

The PRIME trial, a phase III study, showed that patients with wild-type KRAS tumors achieved statistically significant improvement in PFS with panitumumab and FOLFOX4 versus FOLFOX4 alone (9.6 versus 8.0 months, P=0.02) and a nonsignificant improvement in OS versus FOLFOX4 alone (23.9 versus 19.7 months, P =0.07). In contrast, patients with mutant KRAS had significantly reduced PFS with panitumumab-FOLFOX4. [113]

Thus, panitumumab becomes an option, or an alternative to cetuximab, for patients who have tumors with wild-type KRAS. [114, 115] However, Hecht et al reported that adding panitumumab to bevacizumab and chemotherapy (oxaliplatin- and irinotecan-based) as first-line treatment of metastatic colorectal cancer resulted in increased toxicity and decreased PFS. [116]

In a randomized study of first-line treatment of metastatic colorectal cancer, Bokemeyer et al concluded that the overall response rate for cetuximab plus FOLFOX-4 was higher than with FOLFOX-4 alone. However, a statistically significant increase was seen only in patients with KRAS wild-type tumors, for whom the addition of cetuximab increased chance of response and lowered the risk of disease progression. [117]

Douillard and colleagues reported that in addition to KRAS mutations in exon 2, additional RAS mutations (KRAS exon 3 or 4; NRAS exon 2, 3, or 4; or BRAF exon 15) are associated with inferior PFS and OS with panitumumab-FOLFOX4 treatment. [118] Other mutations that involve some of the kinases downstream from KRAS (such as BRAF and PI3K) are being investigated and may result in even more selective methods to identify patients that may benefit from EGFR inhibition.


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