Adding Vectibix (panitumumab) to standard chemotherapy improved overall survival compared with Avastin (bevacizumab) for people with left-sided metastatic colorectal cancer, though those with right-sided tumors didn’t see the same benefit, according to study results presented at the 2022 American Society of Clinical Oncology (ASCO) Annual Meeting.
“This trial shows the longest survival ever reported in a first-line unresectable metastatic colorectal cancer prospective Phase III trial,” said Cathy Eng, MD, of Vanderbilt-Ingram Cancer Center. “These findings emphasize the importance of taking into account sidedness as well as including comprehensive biomarker testing, especially for the status of the RAS gene, which is critical for all colorectal cancer patients at the time of diagnosis of metastatic disease.”
Takayuki Yoshino, PhD, of the National Cancer Center Hospital East in Kashiwa, Japan, and colleagues conducted a clinical trial (NCT02394795) to evaluate the efficacy of Vectibix versus Avastin in combination with a standard first-line chemotherapy regimen known as mFOLFOX6 (leucovorin calcium, fluorouracil and oxaliplatin).
Between May 2015 and June 2017, the researchers enrolled 823 individuals with newly diagnosed metastatic colorectal cancer associated with the RAS gene. Of these, 604 had left-sided tumors. The participants were randomly assigned to receive Vectibix or Avastin, two monoclonal antibodies, in addition to mFOLFOX6.
After five years of follow-up, the Vectibix combination significantly improved overall survival compared with the Avastin combination for people with left-sided tumors.
Participants who took Vectibix lived for 37.9 months compared with 34.3 months for those who received Avastin, representing an 18% lower risk of death. The response rate (tumor shrinkage) and curative resection rate (no remaining cancer after surgery) were both higher with Vectibix, while progression-free survival was similar with both therapies.
However, for those with right-sided tumors, the difference in overall survival in the Vectibix and Avastin groups was not statistically significant.
“This trial demonstrates that if gene testing shows that a tumor is RAS wild-type, the choice of initial treatment with panitumumab plus mFOLFOX6 chemotherapy is superior to initial treatment with bevacizumab plus mFOLFOX6 chemotherapy for those people with left-sided tumors,” Yoshino said in an ASCO press release. “It has long been believed that the sequence of metastatic colorectal cancer treatment does not matter as long as patients had access to the drugs at some point, which has now been disproven.”
Click here to read the ASCO abstract.