Phase III Multicenter Clinical Trial of the Sialyl-TN (STn)-Keyhole Limpet Hemocyanin (KLH) Vaccine for Metastatic Breast Cancer

Purpose. This double-blind, randomized, phase III clinical trial evaluated time to progression (TTP) and overall survival in women with metastatic breast cancer (MBC) who received sialyl-TN (STn) keyhole limpet hemocyanin (KLH) vaccine. Secondary endpoints included vaccine safety and immune response. Experimental design. The study population consisted of 1,028 women with MBC across 126 centers who had previously received chemotherapy and had had either a complete or a partial response or no disease progression. All women received one-time i.v. cyclophosphamide (300 mg/m 2 ) 3 days before s.c. injection of 100 g STn-KLH plus adjuvant (treatment group) or 100 g KLH plus adjuvant (control group) at weeks 0, 2, 5, and 9. Subsequently, STn-KLH without adjuvant or KLH without adjuvant was then administered monthly for 4 months, and then quarterly until disease progression, without cyclophosphamide. Results. STn-KLH vaccine was well tolerated; patients had mild to moderate injection-site reactions and reversible flu-like symptoms. Week-12 antibody testing revealed high specific IgG titers and a high rate of IgMto-IgG seroconversion; the median IgG titers in STnKLH recipients were 320 (anti-ovine submaxillary