Original StudyImpact of Primary Tumor Site on Bevacizumab Efficacy in Metastatic Colorectal Cancer
Introduction
Colorectal cancer (CRC) is a heterogeneous disease that evolves through varied genetic and epigenetic molecular pathways.1, 2 In 1990, Bufill proposed the concept of developmental and biologic differences in the proximal and distal colon resulting in differing susceptibility to neoplastic transformation, with proximal and distal colon cancers arising through different pathogenic mechanisms.3 Findings of varying molecular genetic alterations in proximal and distal cancers supported this concept.4 Since then, growing evidence regarding molecular changes at colonic subsites has supported as well as challenged the dichotomy of proximal (right-sided) colon versus distal (left-sided) colorectum divided at the splenic flexure.5, 6, 7, 8, 9, 10
Regardless of whether a strict right- versus left-sided dichotomy exists or molecular changes occur as a continuum, clear differences between cancers of the right colon and the left colorectum have been observed—eg, right-sided tumors are associated with CpG island methylator phenotype–high and microsatellite instability–high and with BRAF mutations, and left-sided tumors exhibit chromosomal instability.9, 11, 12 These factors may contribute to variations in patient outcomes, with consistent reports of the association of right-sided tumors and poorer prognosis.7, 10, 12, 13 Importantly, in the era of personalizing the management of metastatic CRC (mCRC), emerging data highlight the potential importance of primary tumor location (proximal vs. distal) in predicting response to targeted therapies. Indeed, 3 recent analyses reported that in patients with KRAS wild-type tumors, the efficacy of the anti–epidermal growth factor receptor (EGFR) monoclonal antibody cetuximab was confined to left-sided tumors (positioned at or distal to the splenic flexure).14, 15
For the anti-VEGF (vascular endothelial growth factor) agent bevacizumab, results to date regarding the impact of primary tumor site are conflicting. Boisen et al16 concluded the impact of bevacizumab may be site specific. In their analysis of an initial cohort of 213 patients who received capecitabine and oxaliplatin (CAPOX) alone, they found no impact of primary site on progression-free survival (PFS) or overall survival (OS). In a later cohort of 667 mCRC patients treated with CAPOX and bevacizumab, the authors noted superior survival outcomes in patients with sigmoid and rectal primary cancers versus those with colon cancers at any other location. In contrast, using the more traditional definition of proximal (right-sided) versus distal (left-sided) tumors (division at the splenic flexure), Loupakis et al, in an analysis of 3 independent studies where patients with mCRC received first-line chemotherapy with or without bevacizumab, found no association between tumor location and bevacizumab efficacy.8, 17
The present prospective observational study of consecutive mCRC patients treated in routine clinical practice sought to address the issue of potential interaction, if any, between primary tumor site and bevacizumab efficacy. We used data from TRACC (Treatment of Recurrent and Advanced Colorectal Cancer), a prospective multicenter Australian registry of consecutive patients with mCRC18 that utilizes a clinician-designed data set that includes key prognostic information such as Eastern Cooperative Oncology Group (ECOG) performance status (PS), comorbidities, and treatment intent. Using the traditional definition of left- versus right-sided mCRC (division at splenic flexure) with rectal tumors considered a separate entity, we assessed whether the location of the primary tumor was a predictor of PFS in patients receiving bevacizumab concurrently with first-line chemotherapy. Additionally, we conducted a similar analysis for a subgroup of tumors classified based on the alternative definition by Boisen et al16 of right and left colorectal tumors (right-sided, cecum to descending colon; left-sided, sigmoid and rectal tumors) to determine if the variation in definition could account for the differences reported.
Section snippets
Study Population and Description
The TRACC registry, a prospective multicenter registry enrolling consecutive patients with mCRC from centers across Australia, has been described previously.18 Key data points pertaining to patient and disease characteristics, treatment, and outcomes are collected in an electronic database at the point of care. For this analysis, all patients diagnosed between January 2009 and December 2014 who received first-line chemotherapy with palliative intent were included. Patients with multiple primary
Study Population
At the time of data analysis, 1604 patients with mCRC from 16 sites were registered within the TRACC database. Of these, 926 satisfied the inclusion criteria (297 had right-sided primary tumors, 354 had left-sided tumors, and 275 had rectal tumors). The study population's median age was 65.6 years (range, 26-92 years), and patients were followed for a median of 32.5 months.
Table 1 depicts baseline parameters. Patients with right-sided primary tumors were significantly older (median age, 68.6
Discussion
The findings of the present study concur with previous reports6, 7, 13 indicating that primary tumor location is a prognostic variable in mCRC, with right-sided tumors (proximal to the splenic flexure) associated with the least favorable survival outcomes and with the longest PFS and OS being seen in patients with rectal tumors. We also confirmed the role of baseline ECOG PS as an independent prognostic variable regardless of treatment administered, and that provision of bevacizumab alongside
Disclosure
The authors have stated that they have no conflict of interest.
Acknowledgments
Roche Products Pty Limited provided financial assistance for the development, installation, and maintenance of the TRACC registry. We thank all the participating centers of the TRACC registry who contributed to data collection and BioGrid Australia. We also thank Nalini Swaminathan for her writing assistance.
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The first 2 authors contributed equally to this article, and both should be considered first author.