GcMAF is a protein produced by altering the vitamin D of the binding protein.
Biochemically, GcMAF results from the sequential deglycosylation of the vitamin D-binding protein (the Gc protein), which is naturally favored by lymphocytes (B and T cells). The resulting protein may be a macrophage activating factor (MAF). MAFs are lymphokines that control the expression of antigens on the surface of macrophages and one of the functions of which is to make macrophages cytotoxic to tumors.
False claims of cancer cure
As of 2008, GcMAF has been promoted as a cure for cancer, HIV, autism and other conditions.
Three of the four original studies written by Yamamoto (published between 2007 and 2009) were canceled by the scientific journals in which they were published in 2014, officially due to irregularities in the way in which ethical approval was granted.     The reasons for retraction also included methodological errors in the studies.   The integrity of the research, led by Nobuto Yamamoto and his colleagues, which initially provoked claims about cancer and HIV was questioned.  
The UK Medicines and Health Products Regulatory Agency  and Cancer Research UK have warned the public of false claims of clinical benefit, incorrectly based on reduced levels of the alpha – N – acetylgalactosaminidase enzyme (also known under the name of nagalase), the production of which could be increased in many cancers. 
In 2014, the Belgian Anticancer Fund raised serious concerns about studies published on GcMAF by Yamamoto and his colleagues. 
In 2015, the UK Medicines and Health Products Regulatory Agency (MHRA) closed a GcMAF manufacturing facility for the treatment of cancer. 
In 2014, an Israeli company called Efranat was conducting a clinical trial of GcMAF in people with various types of cancer in a hospital in Israel.  In December 2017, Efranet had obtained an orphan designation from the FDA for the use of GcMAF in recurrent respiratory papillomatosis  and reported conducting a phase I trial in Israel.