BCG instillation is one of the most effective local cancer treatments in all of medicine. Here is a plain language explanation of what it involves, how it works, and what you will experience.
Your bladder cancer has been treated with TURBT — the endoscopic surgery that removed the tumour from the bladder lining. Your urologist has now recommended BCG. You may have been told it is an injection into the bladder, you may have heard it is related to the tuberculosis vaccine, and you may be wondering what on earth you are about to go through.
Let me explain it clearly.
BCG stands for Bacillus Calmette-Guérin — a weakened, attenuated strain of Mycobacterium bovis, the same bacteria used in the tuberculosis vaccination given to children. It has been used as a bladder cancer treatment since the 1970s and remains one of the most effective local cancer therapies ever developed.
BCG is used for non-muscle invasive bladder cancer (NMIBC) — cancer confined to the inner lining of the bladder. After TURBT removes the visible tumour, BCG is instilled directly into the bladder to prevent recurrence and reduce the risk of progression to muscle-invasive disease.
TURBT removes the visible tumour but microscopic cancer cells often remain on the bladder surface. BCG stimulates the immune system to seek out and destroy these residual cells. Without BCG, high-risk NMIBC recurs in up to 70% of patients within 5 years. With BCG, this is significantly reduced.
BCG does not directly kill cancer cells. Instead, it triggers a local immune response in the bladder wall — attracting white blood cells that identify and destroy cancer cells. This is why side effects feel like an immune response (irritation, mild fever) rather than the systemic toxicity of traditional chemotherapy.
When BCG is instilled into the bladder, it attaches to the bladder lining and triggers an intense local inflammatory response. Immune cells flood the bladder wall, releasing cytokines that destroy both BCG bacteria and any residual tumour cells. This immune activation also creates immunological memory — the bladder remains primed to recognise and attack bladder cancer cells even after treatment ends.
BCG is recommended for intermediate and high-risk NMIBC. Risk stratification is based on tumour grade, size, number, recurrence history, and the presence of CIS (carcinoma in situ — a flat, high-grade lesion).
Low-risk, small, single, low-grade tumours may be managed with a single immediate instillation of chemotherapy (mitomycin C) after TURBT, without requiring a full BCG course.
BCG instillation is a simple outpatient procedure that takes approximately 15–20 minutes. Here is exactly what happens:
You are asked to empty your bladder before arriving. A thin catheter is passed through the urethra into the bladder — this takes a few seconds and causes brief discomfort. The BCG solution (50 mL) is instilled through the catheter into the bladder. The catheter is removed immediately after.
You then retain the BCG in your bladder for 2 hours. During this time you are asked to change position periodically — lying on your back, each side, and your front — to ensure the BCG contacts all areas of the bladder lining. After 2 hours, you urinate normally to void the BCG.
For 6 hours after each BCG instillation, add bleach (household sodium hypochlorite) to the toilet before flushing — this inactivates the BCG in the urine. This is a safety precaution for household contacts, particularly those who are immunocompromised. Wash hands thoroughly after voiding. Men should sit to urinate during this period to avoid splashing.
One instillation per week for 6 consecutive weeks. This is the initial treatment course. The 6-week gap allows the immune response to build progressively.
A cystoscopy (bladder camera examination) is performed 3 months after completing the induction course to assess the bladder lining and confirm response.
For high-risk disease, maintenance BCG significantly improves outcomes. The standard schedule (SWOG protocol) involves 3 weekly instillations at each of these time points over 3 years.
Regular cystoscopies continue throughout and after BCG treatment to monitor for recurrence. NMIBC requires lifelong cystoscopic surveillance.
You have active symptoms of a urinary tract infection on the day of instillation — BCG should be postponed until the infection is treated. You have visible blood in the urine from traumatic catheterisation. You are immunocompromised (HIV, on immunosuppressants after organ transplant) — discuss with your urologist. You are pregnant or breastfeeding.
BCG is not a pleasant treatment — the weekly visits, the urinary symptoms, the fatigue are real. But it is one of the most effective local cancer treatments in medicine, and for high-risk NMIBC it significantly reduces both recurrence and the risk of progression to muscle-invasive cancer that would require bladder removal.
Complete the full course. Attend every cystoscopy. Report side effects that concern you promptly. And know that the discomfort is temporary — the protection it provides is not.
This article is written for general patient education. BCG treatment protocols vary based on tumour risk stratification and institutional practice. Always follow the specific guidance of your treating urologist.