A Real-World Retrospective Study to Evaluate the Reliability of Cetuximab plus Capecitabine versus Capecitabine as Maintenance Therapy in Patients with RAS and BRAF Wild-Type Metastatic Colorectal Cancer

Colorectal cancer (CRC) is one of the most common malignant tumors of the digestive system, and its incidence and mortality rates have increased in recent years. On the basis of the latest global cancer data from 2020, as released by the World Health Organization’s International Agency for Research on Cancer (IARC), there were 1.93 million new cases and 940,000 deaths resulting from CRC globally in 2020, ranking third in incidence and second in mortality [1]. With the continuous progress of medical technology, the treatment of metastatic colorectal cancer (mCRC) is gradually improving. The proportion of patients who achieve a state of stability in regard to the disease (stable disease [SD]) via palliative chemotherapy is approximately 50% [2, 3]. Although many studies suggested that patients who achieve partial or complete remission have a better prognosis, patients who also achieve SD may have variable prognoses due to different biological characteristics [4]. A meta-analysis compared the safety and efficacy of maintenance therapy, continuous therapy, and chemotherapy-free intervals (CFIs) alone, and showed that in terms of progression-free survival (PFS), maintenance therapy was better than CFIs alone [5]. PFS and overall survival (OS) were similar in the maintenance and continuous strategies, while the safety of the maintenance strategy was better. However, maintenance therapy for RAS and BRAF mCRC lacks standard treatment protocols and needs to be explored in depth.

It was found that in patients with RAS mCRC, the anti-epidermal growth factor receptor (EGFR) monoclonal antibody cetuximab showed good effects. However, there are few relevant studies on whether cetuximab-capecitabine can be used as a maintenance treatment for RAS and BRAF mCRC after cetuximab-FOLFIRI and whether the disease is controlled. Therefore, the aim of this study was to analyze the reliability of cetuximab-capecitabine as a maintenance therapy for patients with RAS and BRAF mCRC who received at least six cycles of induction therapy compared with maintenance therapy via capecitabine alone, with the hope of providing a basis for future clinical trials.

This single-center retrospective analysis was based on real-world data. Among the patients with mCRC who received cetuximab plus FOLFIRI from January 2016 to October 2020 in our hospital, data on patient treatment were collected and patients meeting the following criteria were selected and enrolled in the study: (1) age 18–75 years; (2) PS score 0–1; (3) pathologically confirmed to have colorectal adenocarcinoma; (4) in which imaging confirmed distant metastasis and inoperable radical resection; (5) had both RAS and BRAF wild-type; (6) had received cetuximab plus FOLFIRI as standard first-line chemotherapy (cetuximab 500 mg/m², d1; calcium folinate 400 mg/m², intravenous drip 120 min, d1; irinotecan 180 mg/m², continuous intravenous drip 30–90 min, d1; 5-fluorouracil 400 mg/m², intravenous injection, d1; 5-fluorouracil 2,400 mg/m², continuous intravenous pump for 46 h for 2 weeks as a cycle, and controlled after at least 6 cycles of the above induction therapy – efficacy evaluation of complete response, partial response, and SD); (7) whose liver, kidney, and blood functions were within one degree of impairment before entering maintenance therapy; and (8) who had received at least one maintenance treatment. The exclusion criteria were as follows: (1) severe cardiac, pulmonary, hepatic, or renal insufficiency; (2) diagnosis with a history of neurological disease; (3) incidence of a resection of the primary tumor or metastases during induction chemotherapy; (4) indication of a response evaluation as progressive disease after completion of chemotherapy.

Patients in the observation group received cetuximab plus capecitabine as maintenance therapy: cetuximab 500 mg/m², d1, every 2 weeks; capecitabine 1,000 mg/m² bid, 1–14 days, every 3 weeks. Patients in the control group were treated with capecitabine 1,000 mg/m² bid on days 1–14, every 3 weeks. We analyzed the data from the two groups retrospectively. The primary endpoint was PFS after maintenance treatment, which was defined as the time from the start of maintenance treatment to progression, death, or the date of the last follow-up for disease progression. The secondary endpoints were the safety of both treatments, including adverse reactions and adverse reaction grades. The objective response evaluation in this study was performed according to RECIST 1.1. The initiation of maintenance therapy was used as the patient baseline. Clinicopathological data including gender, age, primary tumor site, PS score, impact of primary tumor resection, metastasis time, pathological differentiation, baseline carcinoembryonic antigen (CEA) level, microsatellite instability (MSI) status, tumor metastasis site, number of metastasis sites, number of induction treatment cycles, and best response to induction therapy were collected and followed up on until March 2021, with follow-up visit once in 2 months. The observation group mean follow-up time was 7.0 months, with a first quartile of 4.5 months and the third quartile equaling 9.7 months; the follow-up time of the control group was 6.2 months, with a first quartile of 4.9 months and a third quartile of 7.8 months. In this study, data were collected through patient examination reports and telephone visits. To ensure the accuracy of patient data, both telephonic and clinical examinations of patients were conducted regularly. Patients were communicated with as much as possible before conducting the experiment, explaining the importance of this experiment, completing the entire experiment as much as possible, and excluding patients with missing data if there was a case of complete data patching.

Statistical analyses of data were performed employing the SPSS 25.0 software. The baseline characteristics and disease factors of patients were summarized using descriptive statistics and analyzed using the t test. The classified data were analyzed by χ² test and Fisher’s exact test. Some important factors associated with the prognosis of the research objects were analyzed by univariate Kaplan-Meier and Cox proportional analysis. Survival time was calculated using the Kaplan-Meier method, hazard ratio (HR). The effect of treatment modality or factor on disease risk was assessed by comparing disease incidence between groups, a 95% confidence interval (CI) determined via Cox regression, and p values analyzed using the log-rank test. The incidence of adverse events (AEs) was analyzed by Fisher’s exact test. Statistical significance was set at p < 0.05.

A total of 39 patients with RAS and BRAF mCRC who received at least six cycles of treatment with cetuximab plus FOLFIRI at Huizhou Municipal Central Hospital from January 2016 to October 2020 participated in this study; 18 and 21 patients were in the observation and control groups, respectively. An independent samples t test showed that there was no significant difference in baseline demographic and general clinical characteristics between the two groups (p > 0.05) (Table 1), which indicated that the baselines were comparable without further propensity score matching.

The Kaplan-Meier survival curve analysis indicated that the mPFS was 9.5 months (95% CI = 6.4–12.6) in the observation group, and 7.3 months (95% CI = 5.8–8.8) in the control group (HR = 0.4, 95% CI = 0.2–1.0, p = 0.039). The median treatment cycles of cetuximab and capecitabine were 13.5 and 8.5 cycles, respectively; the median treatment cycle of capecitabine was 8.0 cycles in the control group (Fig. 1; Table 2).

We took the different maintenance treatment regimens of the two groups as the main research focus and adjusted for a number of variables such as gender, age, primary tumor site, PS score, whether the primary tumor was resected, metastasis time, pathological differentiation, baseline CEA level, MSI status, tumor metastasis site, number of metastasis sites, number of induction treatment cycles, and best response to induction therapy. We observed that the multivariate Cox proportional hazards regression analysis to show that, when compared with capecitabine maintenance treatment, cetuximab plus capecitabine maintenance treatment reduced the risk of disease progression by an average of 60% (HR = 0.4, 95% CI = 0.1–1.0, p = 0.041) (Table 2).

Univariate analysis showed no significant difference in mPFS based on gender, age, PS score, whether the primary tumor was resected, metastasis time, pathological differentiation, MSI status, tumor metastasis site, number of metastatic sites, and best response to induction therapy (p > 0.05). However, there was a significant difference in mPFS based on the primary tumor site and baseline CEA level (p < 0.05) (Table 3). Multivariate Cox proportional analysis indicated that primary tumor site, baseline CEA level, and MSI status were independent prognostic factors with mCRC patients (Fig. 2). Among them, the mPFS was 8.0 months (95% CI = 4.8–11.2) for the primary site of the left colon, 6.6 months (95% CI = 5.6–7.7) for the primary site of the rectum (HR = 0.1, 95% CI = 0.0–0.6); 9.5 months (95% CI = 6.7–12.3) for the low level of CEA, 6.2 months (95% CI = 4.4–8.0) for the high level of CEA (HR = 0.1, 95% CI = 0.0–0.3); 7.8 months (95% CI = 7.2–8.5) for the MSS/MSI-L, 5.9 months for the MSI-H, and 7.4 months (95% CI = 7.1–7.7) for the unmeasured MSI status (HR = 0.4, 95% CI = 0.2–0.8).

Nine patients (50.0%) in the observation group (cetuximab plus capecitabine) experienced treatment-related grades 3–4 AEs, and 6 patients (33.3%) in the control group (capecitabine) experienced treatment-related grades 3–4 AEs (Table 4). The overall incidence of rash and acne in the observation group was significantly higher (p < 0.05). There were no deaths caused by treatment-related AEs in the study. Most of the AEs were mild and manageable.

CRC is very common in human malignant tumors. Given its low rate of early diagnosis, a majority of patients are in the middle and late stages of progression at the time of their diagnosis. Chemotherapy is an important means of CRC treatment; however, exposure to chemotherapy drug toxicity reduces patient compliance with long-term induction therapy, and discontinuation increases the possibility of recurrence [6]. Therefore, with the gradual increase of OS in mCRC patients, the idea of effective, low-cost, and less harmful therapy has been widely accepted. The current study shows that it is not clear which treatment modalities bring the greatest benefit to patients for the three treatment modalities: maintenance therapy, complete CFIs, and continuous treatment. The purpose of this study was to investigate the efficacy of cetuximab combined with capecitabine with RAS and BRAF wild-type mCRC by placing cetuximab combined with FOLFIRI in patients whose disease has been controlled for more than six cycles of initial therapy. In terms of the reliability of maintenance therapy, the results showed that the PFS of cetuximab plus capecitabine was longer than that of capecitabine alone. This result is similar to the results of previous studies. Zhao et al. [5] conducted a meta-analysis of six trials (N = 2,454 patients) to compare the reliability of these three treatment strategies; they concluded that maintenance therapy was superior to CFI in terms of PFS (HR = 0.53, 95% CI = 0.40–0.69); although the maintenance strategy was similar to the CFI strategy in OS (HR = 0.84, 95% CI = 0.70–1.00), it also suggested that sequential maintenance after induction therapy resulted in a reduced risk of mCRC recurrence compared with complete CFI after induction therapy. In addition, PFS and OS were comparable between the maintenance and continuous treatment groups (HR = 1.18, 95% CI = 0.96–1.46; HR = 1.05, 95% CI = 0.98–1.27), and the incidence of toxicities such as neutropenia, neuropathy, hand-foot syndrome, and fatigue in grades 3–4 was lower in the maintenance group than in the continuous treatment group. Thus, maintenance treatment not only reduced cumulative grades 3–4 toxicities but also showed efficacy similar to that of the continuous strategy.

The OPTIMOX1 study [7] evaluated a new strategy for intermittent treatment of oxaliplatin based on FOLFOX7, randomizing previously untreated patients with FOLFOX4 every 2 weeks until progression (group A) or FOLFOX7 treatment for six cycles, maintenance without oxaliplatin for 12 cycles, and reintroduction of FOLFOX7 (group B). The results showed that the PFS and OS were, respectively, 9.0 months and 19.3 months in group A, and 8.7 months and 21.2 months in group B, and that the difference was not statistically significant. These results suggest that, in the FOLFOX regimen, oxaliplatin can be safely stopped after six cycles of use, and that the PFSOS were similar between maintenance therapy and continuous therapy. In the GERCOR OPTIMOX2 study [8], which compared the effects of stopping chemotherapy and maintaining leucovorin calcium and fluorouracil (FOLFOX) treatment after six cycles of leucovorin, fluorouracil, and oxaliplatin (FOLFOX) chemotherapy, 202 patients with untreated mCRC were randomly divided into two groups: 98 patients in the maintenance group received six cycles of modified FOLFOX7 (mFOLFOX7) followed by sequential leucovorin calcium and fluorouracil maintenance until progression, while 104 patients in the complete CFI group received complete stopping chemotherapy after six cycles of mFOLFOX7 chemotherapy, while mFOLFOX7 was reintroduced after tumor progression in both arms, with the primary study endpoint of time to disease control (DDC). The results showed that the mean DDC was 13.1 months in the maintenance group and 9.2 months in the CFI group (p = 0.046). The PFS and OS rates were, respectively, 8.6 and 23.8 months in the maintenance group, and 6.6 and 19.5 months in the CFI group. Thus, planned complete discontinuation of chemotherapy had a negative impact on DDC and PFS compared with a maintenance strategy.

The RAS gene is one of the most important oncogenes. In mCRC, approximately 50% of patients have RAS gene mutations. KRAS accounts for the largest proportion of RAS mutations, with a mutation rate fluctuating between 30% and 45%. The efficacy of EGFR-targeting antitumor agents, including cetuximab and panitumumab, in CRC patients is correlated with the status of RAS gene mutations, and just wild-type patients are able to benefit from it [9]. Therefore, RAS status has some predictive effect in CRC treatment.

Previous studies have shown that anti-EGFR in combination with 5-FU was better tolerated, while capecitabine has some advantages over 5-FU in terms of treatment modality and safety, and has improved the quality of life of patients to some extent. Therefore, capecitabine was selected for follow-up treatment in this study [10]. This observation shows that the anti-EGFR monoclonal antibody cetuximab combined with capecitabine maintenance therapy is better than capecitabine alone, indicating the importance of cetuximab in the maintenance therapy of wild-type mCRC. Importantly, there were no deaths due to treatment-related AEs during maintenance therapy. There was, nonetheless, a statistically obvious difference in the incidence of rash and acne between the observation and control groups (p < 0.05), whereas there was no obvious difference in the incidence of grades 3–4 rash and acne between the two groups (p > 0.05). Most of the unfavorable incidents were mild and manageable. A systematic evaluation and meta-analysis by Parisi A et al. [11] showed better efficacy of RAS wild-type mCRC after anti-EGFR treatment. This is similar to previous studies that have confirmed the effectiveness of anti-EGFR monoclonal antibodies as a treatment to maintenance for KRAS wild-type mCRC. In the MACRO-2 study [12], after 193 patients with RAS mCRC received first-line treatment with FOLFOX plus cetuximab for eight cycles, maintenance treatment with cetuximab was non-inferior to continuous treatment with FOLFOX-cetuximab, with an ORR of 47% versus 39%, a 9-month PFS% of 64% versus 72%, a PFS of 8.9 versus 9.8 months, and an OS of 23.6 versus 22.2 months, all of which were not statistically significant. In terms of safety, the incidences of rashes (grade 3), sensory neuropathy, and serious adverse reactions were lower than those of maintenance treatment with cetuximab. In the VALENTINO study [13] conducted in a multicenter Italian setting, 229 patients with RAS wild-type mCRC were randomized to either arm A (n = 117) or arm B (n = 112) and received 4 months of induction treatment with panitumumab plus FOLFOX4, followed by maintenance treatment with panitumumab in arm A, and panitumumab plus fluorouracil and leucovorin in arm B. The results showed that the 10-month survival rate was 59.9% (95% CI = 51.5–69.8%) in group A and 49.0% (95% CI = 40.5–59.4%) in group B (HR = 1.51, 95% CI = 1.11–2.07; p = 0.01). Compared with group B, the incidence of grade three or more treatment-related AEs was higher in group A (36 [42.4%] vs. 16 [20.3%]) and the incidence of panitumumab-related AEs (27 [31.8%] vs. 13 [16.4%]). Thus, the PFS of the maintenance treatment with panitumumab was inferior to that of panitumumab plus fluorouracil and leucovorin, however, the latter had slightly higher treatment toxicity. The COIN-B study [14] showed that after 12 weeks of induction treatment with cetuximab plus FOLFOX regimen, compared with intermittent treatment, maintenance treatment with cetuximab improved failure-free survival by 2.1 months (14.3 vs. 12.2 months) and OS by 5.4 months (22.2 months vs. 16.8 months) without increasing AEs. Li et al. [15] initiated a single-arm, open, multicenter phase 2 clinical trial that included 47 patients with initially untreated RAS wild-type progressive CRC. After 4–6 months (or 8–12 cycles) of first-line fluorouracil combination chemotherapy plus cetuximab induction therapy, 13 patients with SD, partial response, or complete response were evaluated and entered the maintenance treatment period of cetuximab plus capecitabine with a maintenance PFS of 7.2 months. The study results showed that after 4–6 months of induction therapy, the PFS was 16.7 months after first-line treatment and 12.1 months during maintenance treatment in patients treated with capecitabine plus cetuximab maintenance therapy, and that the treatment-related toxicities and adverse reactions were tolerable during the maintenance period. In addition, the study by Kienle [16] and Wang et al. [15] confirmed that maintenance therapy with capecitabine plus cetuximab after initial chemotherapy is a promising new maintenance therapy.

Both the MACRO-2 [12] and VALENTINO [13] studies investigated the reliability of single-agent anti-EGFR monoclonal antibody compared with anti-EGFR monoclonal antibody plus chemotherapy in maintenance therapy, while the COIN-B study compared the reliability of maintenance therapy with anti-EGFR monoclonal antibody versus observation alone in CFI. Wang’s [15] study was a single-arm trial that assessed the reliability of anti-EGFR plus oral chemotherapy versus oral chemotherapy alone as maintenance therapy for mCRC with RAS and BRAF wild-type status. The results showed that the PFS time was significantly prolonged in the combined maintenance therapy group, and that the tolerability in the maintenance phase was fair in both groups.

Our study shows that cetuximab-capecitabine was effective and well tolerated, which could provide a significant benefit to patient survival. However, this retrospective and non-randomized study has some limitations; the small sample size may not easily identify statistically significant differences in baseline patient characteristics, and similarly, the multivariate analysis and propensity score matching analysis based on the Cox proportional risk model and case-control matching analysis may be inadequate. Another limitation of this study is that the follow-up period was not long enough and the study design had some limitations. In the future, multicenter, prospective, randomized controlled studies will be conducted, along with increasing the sample size and refining the experimental design to confirm the possibility and promotion of cetuximab plus capecitabine as maintenance therapy. Second, the short of monitoring of changes in RAS condition following induction treatment with cetuximab plus FOLFIRI, especially when cetuximab is used as a maintenance treatment agent, it is not possible to further analyze the relationship between the efficacy of cetuximab and RAS status in maintenance therapy. In addition, patients with RAS wild-type mCRC have a definite response to cetuximab. Obviously, the results of this study can be confounded by a variety of factors, with major potential drug confounders, aspirin and idle money chemotherapy, and age potentially confounding the experimental results. Our next step is first to expand the sample size for a clinical study with a larger sample size and second to explore whether the BRAF gene affects the efficacy of cetuximab plus capecitabine maintenance therapy after induction therapy in RAS mCRC.

Cetuximab combined with capecitabine as maintenance therapy after at least six cycles of cetuximab combined with FOLFIRI induction therapy with RAS and BRAF mCRC after the disease has been controlled. Furthermore, during maintenance treatment, there were no deaths due to treatment-related AEs, with most AEs having been mild and manageable. Therefore, cetuximab combined with capecitabine as a maintenance therapy can prolong the survival of patients with advanced CRC and is worthy of consideration for clinic.

Authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki (as revised in 2013). The study was approved by the Ethics Committee of Huizhou Municipal Central Hospital of Guangdong Province (NO. 2015012HWZ), and individual consent for this retrospective analysis was waived.

The authors declare that they have no conflicts of interest.

No funding was received for this study.

Jun Li designed the experiments and drafted the manuscript. Hang Zhang and Xuli Guo collected the clinical samples and processed statistical data. Shaoting Dong, Yi Li, and Weizhen Huang performed the experiments and analyzed the data. Xia Yuan designed, supervised the study, and revised the manuscript. All authors read and approved the final version of the manuscript.

All data that support the findings of this study are available from the corresponding author upon reasonable request.