Valrubicin is primarily used in the treatment of bladder cancer, specifically for patients with carcinoma in situ (CIS) of the urinary bladder who have not responded to or cannot tolerate Bacillus Calmette-Guérin (BCG) immunotherapy. It is administered directly into the bladder through intravesical instillation, allowing it to target cancer cells locally while minimizing systemic exposure and side effects. The drug works by inhibiting the function of topoisomerase II, an enzyme crucial for DNA replication and cell division, thereby preventing the growth and proliferation of cancer cells. Its localized application reduces the risk of damage to healthy tissues and organs, making it a suitable option for patients who are not candidates for more aggressive treatments like surgery or systemic chemotherapy.