An estimated 1,200,000 newly diagnosed colorectal cancer(CRC) cases arose worldwide every year, and CRC has become the third most common malignances in China. Especially in urban areas of China, rapid growth of CRC patients has considerably increased the burden of disease. It is well believed that multi-discipline treatment(MDT) including surgery, chemoradiotherapy and target therapy based on individualized characteristics will benefit CRC patients significantly.

Generally, stage II (T3-4N0M0) and stage III (TanyN1-2M0) colorectal carcinoma can be resected by surgery. In 1990s, National Institutes of Health (NIH) suggested that adjuvant chemotherapy should be applied to stage II/III CRC patients to improve their outcomes. As for stage II CRC, results from the QUASA study indicated that adjuvant chemotherapy could improve 5-year overall survival by 3% to 4% for stage II CRC patients. Currently, most of the global guidelines such as National Comprehensive Cancer Network (NCCN) guidelines still recommended adjuvant chemotherapy for stage II/III CRC patients.

In western countries, approximately 50% of the CRC patients were firstly diagnosed after 70 years old. It was reported that in 1980s, the median age of CRC diagnosis in China was 50. However, in 2005 it had reached 58 years old and has kept increasing in recent years. Limited by age-related organ function decline and comorbid conditions, elderly people shows impaired physical and mental tolerance for chemotherapy. Generally for stage II/III CRC patients, both elderly and younger patients shares common principles of chemotherapy, while a large-scale retrospective analysis based on the ACCENT database showed that among all the CRC cases included, patients with the age ≥ 70 only accounted for 17.1%, much lower than normal. Similarly, Shrag and colleagues reported in their investigation that the proportion of patients ≥75 years old undergoing chemotherapy was substantially lower than patients ≤ 75 years old. These evidence implied that elderly CRC patients held much lower acceptance and completion rate of chemotherapy. With respect to outcomes, a pooled analysis including 3351 CRC cases with adjuvant chemotherapy reported no significant difference on both efficacy and adverse effects among groups of various age, indicating elderly patients could achieve the same benefits from adjuvant chemotherapy. Thus, it is essential to improve the acceptance and completion rate by modifying chemotherapy regimen for elderly CRC patients to achieve better prognosis. There was no random controlled trial focusing on the adjuvant chemotherapy for stage II/III elderly CRC patients.

Results of MOSAIC trial showed that adding oxaliplatin to 5-Fu/ leucovorin could significantly improve 5-year survival of stage II/III colon cancer patients, which made the oxaliplatin-based combine chemotherapy (Folfox, Xelox) be recommended by the latest guidelines. In the subgroup analysis of that trial, however, there was no significant improvement detected in stage II patients. Recent analysis from ACCENT database in 2013 indicated that elderly stage II/III CRC patients (≥ 70 yr) acquired no significant benefits from adding oxaliplatin to fluoropyrimidine-based chemotherapy, which suggested monochemotherapy might be a better option for elderly CRC patients.

Capecitabine ( Xeloda®) is the unique oral prodrug of 5-Fu recommended by global guidelines and especially International Society of Geriatric Oncology (SIOG), and it has been verified by clinical trials that in view of efficacy and safety, capecitabine monochemotherapy was equivalent to i.v. 5-Fu/ leucovorin adjuvant chemotherapy. With efficacy retained, a large group of patients prefer capecitabine due to oral administration which can remarkably enhance flexibility and compliance. These advantages make capecitabine a potential ideal choice for elderly patients. According to the NCCN guideline, the standard dosage of capecitabine was 1250mg/m2 .bid. It was well-established that different characteristics such as ethnicity, age and sex could alter the metabolism and change individual tolerance for drugs; hence, there are still controversies on the optimal dose of capecitabine in different populations. The X-Act trial provided a result that among elderly patients (≥ 70 yr) undergoing standard-dose capecitabine adjuvant chemotherapy(1250mg/m2 .bid), 51% of the patients required dose reduction to complete the whole treatment cycle, implying that the recommended 1250mg/m2 .bid. might be an overdose for elderly patients given the fact that only elderly patients with relatively better health (≤ 75 yr, ECOG≤1) were eventually included in X-ACT trial. Chang and colleagues have verified feasibility of a tailored-dose strategy with a starting dose at 1000 mg/m2 .bid in a single-arm study. The European Society for Medical Oncology (ESMO) has also recommended an option of 80% standard dosage (i.e. 1000 mg/m2 .bid) for elderly II/III CRC patients. However, no prospective trial has been conducted yet to confirm this reduced-dose strategy.

Based on current evidence and controversy above, we designed this non-inferiority, phase 3 clinical trial to explore the optimal dosage of capecitabine monochemotherapy for stage II/III elderly CRC patients. Following the results of sample size estimation, 710 postoperative (pT3-4NanyM0 or pTanyN+M0) elderly patients between 70 to 90 years of age were anticipated to be included and randomly divided into two groups (A and B). Patients in group A would receive the standard dose regimen (1,250 mg/m2 twice daily on days 1-14, and repeated on day 22); accordingly the patients in group B would receive the reduced dose regimen (1,000 mg/m2 twice daily on days 1-14, and repeated on day 22). The primary endpoint was 3-year disease free survival (DFS), other outcomes included 3-year overall survival (OS), completion rate, toxic and adverse effects and quality of life (Qol).