LESSONS LEARNED:Novaferon showed moderate efficacy and was well-tolerated in patients with metastatic colorectal cancer (mCRC), especially with the 20 μg injected 3 times a week strategy.Although Novaferon did not provide a survival benefit for mCRC patients who have failed standard treatment, it may play a role in improvement of immune function. BACKGROUND:To observe the efficacy, safety, and optimal dosage of recombinant antitumor and antivirus protein (Novaferon) in treating patients with metastatic colorectal cancer (mCRC) who failed at least two prior palliative regimens. METHODS:We enrolled 108 patients from May 2011 to December 2012. According to different treatment modalities and therapeutic dosages, the participants were randomly divided into four cohorts at a 2:2:2:1 ratio: (a) 20 μg Novaferon (Genova Biotech, Beijing, People's Republic of China, http://www.genovabiotech.net) injected twice per week, (b) 20 μg Novaferon injected 3 times per week, (c) 40 μg Novaferon injected 3 times per week, or (d) saline injected 3 times per week. The primary endpoint was overall survival. RESULTS:There was no significant difference in overall survival among the four cohorts. The 20-μg dose of Novaferon injected 3 times per week had the highest disease control rate (44.0%) at 6 weeks but without significant differences when compared with placebo (p = .159). Major adverse events with Novaferon were influenza-like symptoms, bone marrow suppression, liver dysfunction, and gastrointestinal discomfort. The level of natural killer cells increased and regulatory T cells decreased significantly after treatment with Novaferon, whereas levels in the placebo group remained the same. CONCLUSION:Novaferon showed moderate efficacy and was well tolerated in patients with mCRC, especially with the 20-μg dose injected 3 times per week. Furthermore, Novaferon might improve immune function of these patients.