Intravesical microwave hyperthermia and chemotherapy for non-muscle-invasive bladder cancer

Transitional cell carcinoma is the most common form of bladder cancer. Non-muscle-invasive transitional cell carcinoma is classified as stage Ta when the tumour is confined to the uroepithelium with no spread into the bladder wall or beyond. It is classified as stage T1 when there is spread into the connective tissue layer between the urothelium and the muscle wall. Non-muscle-invasive transitional cell carcinomas can be graded from G1 (low grade, least aggressive) to G3 (high grade, most aggressive). Carcinoma in situ is a form of tumour consisting of aggressive cancer cells which spread within the surface lining of the bladder.

Surgical interventions for non-muscle-invasive transitional cell carcinoma include transurethral resection, in which malignant tissue is removed with an electrocautery device during cystoscopy. Bacillus Calmette-Guérin (BCG) vaccine or chemotherapy drugs may be put directly into the bladder, either as a treatment in itself, or as adjuvant therapy after transurethral resection. Cystectomy may also be necessary in some patients.

Intravesical microwave hyperthermia and chemotherapy can be used as neoadjuvant therapy before transurethral resection, with the aim of eradicating tumours. Alternatively the procedure can be used after transurethral resection, as adjuvant therapy (sometimes referred to as prophylactic treatment), aiming to prevent recurrence. Hyperthermia is believed to have a direct and immune-mediated cytotoxic effect on tumour cells and to improve the efficacy of chemotherapy drugs.

The procedure can be done on an outpatient basis. Using local anaesthetic urethral gel, a balloon catheter (containing a radiofrequency antenna and several insulated thermocouples), is inserted through the urethra into the bladder. Ultrasound is sometimes used to assess the position of the device. The radiofrequency antenna gives off microwaves which heat the superficial layers of the bladder wall. The thermocouples are spread out from the catheter and pushed against the bladder lining. They monitor temperature to help prevent overheating. A solution of a cytostatic agent, usually mitomycin C, is instilled into the bladder, between the bladder wall and the balloon surface. The solution is continuously pumped out of the bladder, cooled, and recirculated to prevent overheating. Treatment sessions typically last between 40 minutes and 60 minutes and are usually repeated weekly for 4 to 8 weeks, or longer for adjuvant treatment.