Bacillus Calmette Guérin (BCG)

• ATC CODE: 103AX03
• ALSO KNOWN AS: BCG Live, Pacis BCG Live, TICE BCG

DEFINITION: Bacillus or Bacilli Calmette-Guérin (BCG) solution is an immunotherapeutic agent containing live, weakened bacteria. It is approved by the US Food and Drug Administration (FDA) as a primary therapy for carcinoma in situ of the urinary bladder. The BCG solution for bladder cancer contains water, saline, and a freeze-dried and live (but avirulent) strain of Mycobacterium bovis, an organism that causes tuberculosis in cattle.

The BCG vaccine is used throughout the world to immunize humans against tuberculosis, with varying rates of efficacy; the BCG vaccine is not routinely administered in the United States. BCG is named for the two Pasteur Institute researchers who discovered the vaccine against human tuberculosis: physician Léon Charles Albert Calmette (1863–1933) and bacteriologist Jean-Marie Camille Guérin (1872–1961).

Cancers treated: Superficial or early-stage bladder cancer in which tumors have not entered the muscle layer of the bladder wall

Delivery routes: Instillation

How this substance works: Generally, BCG treatment follows surgery to remove tumors from the surface (epithelium) of the inside of the bladder (lumen). A healthcare provider inserts a catheter to deliver the BCG solution to the bladder. The solution remains in the bladder for at least two hours. The millions of M. bovis bacteria in BCG solution stimulate the immune system to seek out and destroy cancer cells. Patients usually have a series of weekly instillations over a number of months, followed by maintenance instillations, depending on the treatment plan.

The exact mechanism of action of the BCG solution is unknown. It is thought that certain proteins in the bacteria adhere to the urothelium or lining of the bladder wall. The urothelium then releases a number of cytokines or inflammatory substances that alert the immune system that a pathogen is present. The bacteria may also enter the cancer cells and break down proteins to display on the cancer cell surface, thus flagging it for destruction by the immune system.

Approximately 70 percent of patients respond to initial treatment, and 75 percent of those patients remain free of bladder cancer for more than five years. However, because BCG is used to treat early-stage cancers, the five-year survival rates are high. Further, some studies suggest 25 to 40 percent of patients may not respond to initial treatments and would benefit from the addition of immunotherapy or chemotherapy to the BCG. Because BCG contains live bacteria, patients with compromised immune systems should not be treated with BCG solution. Patients should also not take antibiotics, which would kill the live bacteria and prevent effective treatment.

In the 2020s, BCG continued to be the first line of defense against treating non-muscle invasive bladder cancer, as it continuously showed the ability to prevent the recurrence of bladder tumors and slow the progression of bladder cancer by between 30 and 40 percent. Although it is an effective treatment, medical researchers are interested in improving treatment with BCG by combining it with other novel immunotherapies and finding more efficient means of delivery. In the mid-2020s, studies from Weill Cornell Medicine and Memorial Sloan Kettering revealed that BCG therapy induces systemic immune training, reprogramming bone marrow stem cells to produce myeloid cells more effective against cancer.

Side effects: Most patients (80 to 90 percent) who receive successive treatments with BCG solution experience one or more side effects, including the urgent need to urinate, blood in the urine, pain during urination, fatigue, nausea, chills, and a low-grade fever that lasts twenty-four to seventy-two hours.

Bibliography

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