Although BCG monotherapy, by then, was known for its potent immune stimulation mechanisms locally (via direct suppression of tumor growth as well as by effective recruitment of immune cells and through increased expression of interferon-gamma (IFN-γ)), it is the role of BCG as an adjuvant to other active agents that caught the attention of the researchers of that time, probably for the increased anti-tumor ability as a combination therapy compared to the monotherapy [86,87,88]. This evidence concerns the gene IFNG and neoplasm.