Mechanisms, Clinical Trials, and New Treatments for BCG-Unresponsive in Nonmuscle Invasive Bladder Cancer.

BACKGROUND

Bacillus Calmette-Guérin (BCG) is the standard adjuvant therapy for high-risk non-muscle invasive bladder cancer (NMIBC), yet treatment failure occurs in 30% to 40% of patients. Those with BCG-unresponsive disease face a high risk of progression and represent a critical unmet need in urologic oncology. This review summarizes the mechanisms of BCG failure and evaluates emerging therapies for BCG-unresponsive NMIBC.

METHODS

We conducted a comprehensive literature review of clinical trials and preclinical studies through August 2025, focusing on therapeutic strategies for BCG-unresponsive NMIBC. Mechanisms of BCG resistance, regulatory definitions, and results from recent Phase II/III trials were analyzed.

RESULTS

Multiple novel therapies have demonstrated efficacy in BCG-unresponsive patients. Immune checkpoint inhibitors (e.g., pembrolizumab) achieved complete response (CR) rates of 41% in carcinoma in situ (CIS) patients. Gene therapies such as nadofaragene firadenovec and CG0070 induced CR rates of 51% and 75%, respectively. Device-assisted therapies including hyperthermic intravesical chemotherapy (HIVEC) showed 24-month recurrence-free survival of 57.4%. The IL-15 superagonist Anktiva (nogapendekin alfa inbakicept), recently FDA-approved, achieved a 71% CR rate with a median duration of 26.6 months when combined with BCG.

CONCLUSIONS

The treatment landscape for BCG-unresponsive NMIBC is rapidly evolving, with immune checkpoint inhibitors, gene therapies, targeted agents, and advanced drug delivery systems showing promising efficacy. These innovations provide bladder-preserving options for patients ineligible for radical cystectomy. Future directions include biomarker-driven therapy selection, combination regimens, and optimized intravesical delivery platforms to improve long-term outcomes.