The Phase III study was designed to assess the efficacy and safety of long-term pegylated interferon alfa-2b versus observation. Researchers randomized patients to either peginterferon alfa-2b adjuvant treatment (n=627) or observation only (n=629) within 70 days of regional lymph node dissection (intent-to-treat population). The endpoint was relapse-free survival (RFS).
Participants randomized to pegylated interferon alfa-2b were to receive a dose of six micrograms/kg/week for an eight-week induction phase followed by three micrograms/kg/wk (maintenance phase), for an intended total treatment duration of five years. Patients randomized to observation received no study treatment.
The study results show that at 3.8 years median follow up, the risk of recurrence or death was reduced by 18% in the pegylated interferon alfa-2b arm compared with observation. The four-year RFS rate was 46% versus 39% in the observation arm.
Median RFS was 34.8 months and 25.6 months in the peginterferon alfa-2b and observation alfa-2b arms, respectively. The improvement in RFS was more pronounced in patients with a lower tumor burden in the lymph nodes based on predefined subgroups.
For the subgroup of patients with clinically non-palpable (microscopic) lymph node disease, the hazard ratio (HR) for RFS was 0.73 in favor of peginterferon alfa-2b treatment, as compared to 0.86 in patients with clinically palpable nodes.
Peginterferon alfa-2b adjuvant treatment was not associated with a benefit on overall survival, a secondary endpoint, with an HR of 0.98.