Aljehani MA, et al. - In a diverse population-based data set of patients receiving systemic chemotherapy (SC) and bevacizumab or cetuximab for metastatic colorectal cancer (mCRC), the association between tumor origin and mortality was determined. The mCRC primary tumor site was shown to be associated with response to biologic therapy (BT; bevacizumab or cetuximab). Regardless of BT type, right-sided primary tumor location was correlated with the highest mortality. Treatment with cetuximab, among patients with wild-type KRAS tumors, proved valuable for those with left-sided mCRC and was associated with significantly poorer survival.

Methods

• Researchers performed this population-based non-concurrent cohort study of statewide California Cancer Registry data.
• All patients aged 40-85 years diagnosed with mCRC and treated with SC only or SC plus bevacizumab or cetuximab from January 1, 2004, through December 31, 2014 were included.
• Patients were stratified by tumor origin in the left versus right sides.
• Treatment regimen included SC or SC plus bevacizumab or cetuximab.
• Mortality hazards were assessed by tumor origin (right versus left sides) for patients receiving SC alone or SC plus bevacizumab or cetuximab.
• For patients with wild-type KRAS tumors, subgroup analysis was also performed.

Results

• For the study,11,905 patients with mCRC were eligible (6,713 men [56.4%] and 5,192 women [43.6%]; mean [SD] age, 60.0 [10.9] years).
• SC and BT were received by 4,632 patients.
• Among patients with right- and left-sided mCRC, SC plus bevacizumab reduced mortality compared with SC alone.
• However, compared with SC alone, SC plus cetuximab reduced mortality only among patients with left-sided tumors and was associated with significantly higher mortality for right-sided tumors (hazard ratio [HR], 1.31; 95% CI, 1.14-1.51; P < .001).
• Right-sided tumor origin was associated with higher mortality among patients receiving bevacizumab (HR, 1.31; 95% CI, 1.25-1.36; P < .001) and cetuximab (HR, 1.88; 95% CI, 1.68-2.12; P < .001) BT among patients treated with SC plus BT, compared with left-sided tumor origin.
• Cetuximab was associated with reduced mortality among only patients with left-sided mCRC compared with bevacizumab (HR, 0.75; 95% CI, 0.63-0.90; P=.002), whereas patients with right-sided mCRC had more than double the mortality compared with those with left-sided mCRC (HR, 2.44; 95% CI, 1.83-3.25, P < .001) in patients with wild-type KRAS tumors (n = 668).