Vitamin D-binding protein-derived macrophage activating factor (GcMAF) appears to be an effective immunotherapeutic agent in patients with metastatic breast cancer, according to US and Japanese researchers. Serum vitamin D-binding protein -- known as Gc protein -- is the precursor of the principal macrophage activating factor," lead investigator Dr. Nobuto Yamamoto told Reuters Health. "Treatment of purified Gc protein with beta-galactosidase and sialidase generates GcMAF," he added, "the most potent macrophage activating factor ever discovered, which produces no side effect in humans." Dr. Yamamoto of the Socrates Institute for Therapeutic Immunology, Philadelphia and colleagues note that in vitro studies show that macrophages treated with GcMAF have a highly tumoricidal effect in mammary adenocarcinomas. To investigate whether the approach can be effective in humans, the researchers studied 16 non-anemic breast cancer patients who were given "a minute amount -- 100 nanograms per week -- of GcMAF," Dr. Yamamoto said. The researchers found that after 16 to 22 GcMAF doses, initially elevated nagalase levels, which reflect the tumor burden, fell to those found in healthy controls. Follow-up over 4 years showed that the level remained low and that there was no tumor recurrence, they report in the January 15th issue of The International Journal of Cancer. The findings, the team concludes, clearly demonstrate "the importance of focusing cancer immunotherapy on macrophage activation."