BCG stands for Bacillus Calmette-Guerin. It was developed in the 1920s. Some readers may recognize this as a vaccine for tuberculosis, as it is still used for this purpose in many countries. BCG is a live, attenuated (weakened) form of the bacteria that causes tuberculosis. Although it is too weak to cause tuberculosis, it does activate the immune system. When it is given as a vaccine, it causes antibodies to be made that are active against the usual form of tuberculosis, thereby preventing most patients from acquiring the disease. For reasons that we still do not fully understand, the immune response to BCG is also able to kill bladder cancer cells.
The bacteria attach to the urothelium and get taken up by the immune system. The immune system then actively destroys the cancerous cells in the bladder.Because it is a live bacteria, BCG should not be given to immunocompromised patients, that is, transplant recipients, HIV patients, patients taking prednisone, or patients with any other condition that may weaken the immune system. This is because immunocompro-mised patients would be at higher risk of developing tuberculosis. BCG should also not be given while there is gross hematuria because there is a higher likelihood of absorbing the bacteria.