Colorectal cancer (CRC) ranks as the third most prevalent cancer and the second leading cause of cancer-related mortality worldwide [1] . In China advanced or metastatic CRC (mCRC), constitute about 20% of the total CRC cases, majority of which are often diagnosed at stage III or IV [2] . Despite advancements in survival rates, mCRC continues to be a fatal condition, with a 5-year survival rate of about 15.7% [3] . Over the last two decades, substantial progress has been made in CRC treatment. The median survival for patients with mCRC undergoing multimodal therapy now exceeds 25 months, yet the prognosis for these patients remains suboptimal [3] [4] .

Metastatic colorectal cancer (mCRC) treatment varies globally based on healthcare resources and access to modern therapies, but systemic therapy remains the standard approach. First-line treatment typically involves chemotherapy regimens like FOLFOX (folinic acid, 5-FU, oxaliplatin) or FOLFIRI (folinic acid, 5-FU, irinotecan) [5] , often combined with targeted biologics. Bevacizumab, an anti-VEGF agent, is commonly used in RAS-mutant tumors at 5 mg/kg biweekly or 7.5 mg/kg every 3 weeks. For RAS wild-type tumors, especially left-sided ones [6] , anti-EGFR drugs like cetuximab (400 mg/m² loading, then 250 mg/m² weekly) or panitumumab (6 mg/kg biweekly) are used. In advanced settings, molecular profiling enables personalized treatments—BRAF V600E mutations are treated with BRAF inhibitors (e.g., encorafenib) plus EGFR inhibitors [7] , while MSI-high or mismatch repair-deficient tumors respond to immune checkpoint inhibitors like pembrolizumab or nivolumab [8] .

Currently, the standard treatment for mCRC remains a combination chemotherapy regimen, mostly either FOLFOX (folinic acid, fluorouracil, and oxaliplatin) or FOLFIRI (folinic acid, fluorouracil, and irinotecan), with the anti-VEGF antibody bevacizumab as the targeted therapy [9] . Bevacizumab functions by inhibiting VEGF, a protein that acts as an endothelial growth factor, facilitating the formation of new blood vessels that tumors rely on to sustain their growth [10] . The combination of bevacizumab with either CapeOX/FOLFOX or FOLRIRI is the most widely used regimen to date due to availability and affordability. Despite this wide spread use hoverer, a pivotal question persists: Does the continued administration of bevacizumab as a second or third line therapy following disease progression provide any discernible clinical advantage? While certain studies suggest its effectiveness as a second or third-line treatment for mCRC, particularly in enhancing progression-free survival (PFS) [11] [12] , the existing evidence remains insufficient to draw definitive conclusions.

In this retrospective study, we investigated and compared the efficacy of bevacizumab combined with capeOX/FOLFOX or FOLFIRI as first, second, or third-line treatment for mCRC. We evaluated the outcomes of bevacizumab combined with either of these two chemotherapy regimens in terms of overall survival (OS) and progression-free survival (PFS).

This was a secondary data analysis conducted on dataset obtained from the publicly accessible DRYAD database ( https://datadryad.org/ ) whose policy states that the data can be used, modified, shared, and redistributed for both commercial and non-commercial purposes without the need for permission, as long as the original author is cited accordingly. Since the data was secondary and publicly available, there was no requirement for ethical approval. The dataset, pertaining to treatment of colorectal cancer using bevacizumab in combination with either capeOX/FOLFOX or FOLFIRI is freely available for download and reuse with proper citation from the Dryad Digital Repository https://doi.org/10.5061/dryad.ft5sk66 . One hundred and fifty four metastatic colorectal cancer patients who underwent bevacizumab-based chemotherapy were initially screened for eligibility. Excluded were those with no pathological diagnosis, no measurable metastatic tumors, and missing drug prescription data. Based on these criteria, seven patients were excluded, leaving 147 participants ( Figure 1 ). Eligible patients received bevacizumab in combination with capeOX/FOLFOX or FOLFIRI regimens, administered as a first, second, or third-line treatment. Bevacizumab was administered intravenously (IV) at a dose of either 5 mg/kg or 7. mg/kg over a 90-minute period every 2 or 3 weeks, prior to the initiation of chemotherapy. capeOX regimen involved oxaliplatin administered at a dose of 130 mg/m² through a 2 - 6 hour infusion on day 1, alongside Xeloda at a dose of 1 g/m² taken twice daily from day 1 to day 14, repeated every 3 weeks. The FOLFOX regimen consisted of oxaliplatin (85 mg/m²) IV over 2 hours, leucovorin (400 mg/m²) IV over 2 hours, and an IV bolus of 5-FU (400 mg/m²), followed by 46 hours of continuous 5-FU IV (2,400 mg/m²). While, the FOLFIRI regimen comprised irinotecan (180 mg/m²) administered via IV infusion over 2 hours, followed by leucovorin (400 mg/m²) IV over 2 hours. This was succeeded by an IV bolus of fluorouracil (5-FU) (400 mg/m²), followed by continuous 5-FU IV (2,400 mg/m²) over 46 hours.

Bevacizumab is a monoclonal antibody used in the treatment of metastatic colorectal cancer (mCRC) due to its ability to inhibit angiogenesis, the process by which tumors develop new blood vessels to support their growth. By binding to and neutralizing vascular endothelial growth factor (VEGF), a protein responsible for promoting blood vessel formation, bevacizumab effectively reduces the tumor’s ability to grow and spread. In this retrospective cohort study, we compared the efficacy and adverse effects of bevacizumab combined with capeOX/FOLFOX, versus bevacizumab combined with FOLFIRI in treating mCRC across the different lines of therapy (1^st, 2^nd and 3^rd line or above).

Our findings revealed that bevacizumab was more effective in prolonging PFS among mCRC patients when combined with FOLFIRI than with capeOX/FOLFOX (HR 0.463 [95% CI: 0.216 – 0.992], p=0.048). Multivariate Cox regression analysis showed that the combination of bevacizumab and FOLFIRI significantly improved PFS (HR 0.463 [95% CI: 0.216 – 0.992], p = 0.048) compared to bevacizumab and capeOX/FOLFOX. This result is consistent with those of Yamazaki et al. [13] who compared the two regimens in a randomized open label phase III trial and found the median PFS for FOLFIRI + Bevacizumab (n = 197) and mFOLFOX6 + Bevacizumab (n = 198) to be 12.1 and 10.7 months, respectively [HR, 0.905; 95% confidence interval (CI) 0.723–1.133; p = 0.003 for non-inferiority]. Similarly, Aranda et al. [14] compared the two regimens and found that Median PFS was 12.4 months (95% CI 11.2 to 14.0) with FOLFIRI-Bevacizumab and 9.3 months (95% CI 8.5 to 10.7) with FOLFOX-Bevacizumab (stratified HR, 0.64; 95% CI 0.49 to 0.82; p=0.0006).

Why the combination of bevacizumab and FOLFIRI (fluorouracil, leucovorin, and irinotecan) has been shown to improve progression-free survival (PFS) in metastatic colorectal cancer (mCRC) patients more effectively than bevacizumab and FOLFOX (fluorouracil, leucovorin, and oxaliplatin) could be due to the distinct mechanisms of action of irinotecan and oxaliplatin, the key drugs in FOLFIRI and FOLFOX respectively. Irinotecan, a topoisomerase inhibitor [15] , is particularly effective against tumors with specific genetic mutations and has demonstrated a better synergy with bevacizumab in targeting the tumor microenvironment, particularly in reducing vascular endothelial growth factor (VEGF) signaling, which is crucial for tumor growth [16] [17] . Additionally, irinotecan can induce more significant tumor cell apoptosis and enhance chemotherapy efficacy [18] . This combination, therefore, may be more potent in inhibiting tumor progression compared to FOLFOX, where oxaliplatin’s mechanisms may not always align as efficiently with bevacizumab’s action on angiogenesis in mCRC. In this study, this synergistic effect was only significant when the combination of bevacizumab and FOLFIRI were used as a second line drug. The reason for this remains unknown.

In this study, the rate of all adverse events monitored were not significant between the two groups. Bevacizumab therapy is often associated with increased rate of hypertension [19] , however, its combination with either capeOX/FOLFOX or FOLFIRI did not significantly increase the rate of hypertension in one group more than the other.

Our study had a few important limitations. Firstly, it was a small, single-centre study, which could introduce bias due to unaccounted and unmeasured confounding factors. Secondly, the sample size was limited, even with the extended follow-up period and broad inclusion criteria. To better understand why the bevacizumab-FOLFIRI combination is more effective in improving PFS in mCRC patients as a second-line treatment, larger-scale prospective studies are needed in the future.

In conclusion, our findings indicate that type of chemotherapy used in combination with bevacizumab is an independent predictor of OS when managing mCRC patients. Furthermore, bevacizumab was more effective in prolonging progression-free survival (PFS) in mCRC patients when combined with FOLFIRI compared to capeOX or FOLFOX. This may be due to the superior synergy between irinotecan, the primary drug in FOLFIRI, and bevacizumab, as opposed to oxaliplatin, the main drug in FOLFOX. This effect was particularly pronounced when used as a second-line treatment. Larger-scale prospective studies are required to confirm these results.

Since the data was secondary and publicly available, there was no requirement for ethical approval.