Novel treatments in BCG failure. Where do we stand today?

Most patients at first diagnosis of bladder cancer (BC) present with non muscle invasive disease (NMIBC). BCG intravesical therapy after transurethral resection of the bladder tumor is the gold standard in intermediate and high risk NMIBC patients. However, it is estimated that approximately 50% of these patients will present with BCG failure which increases their risk for progression to muscle invasive disease. Currently, the best option for these patients is radical cystectomy. Thus, it is of great interest to pursue new, therapeutic options for BCG failure patients to avoid the necessity of radical cystectomy. We hereby review novel treatment modalities for BCG failure patients. METHODS: This is a narrative review. Keywords for the search were BCG failure, BCG unresponsive, BCG refractory, BCG relapsing and BCG intolerance. Evidence was identified through a search for publications with a ''BCG unresponsive'' tag through 2020. Studies were selected if they contained clinical data on BCG unresponsive therapeutics with near-term availability. Clinical trial landscape evaluation for emerging therapies was performed by searching ClinicalTrials.gov for recruiting/ open interventional trials in 2020. RESULTS: Novel treatment modalities for BCG failure include intravesical chemotherapy, BCG re-challenge or combination of BCG with IFN-α2β, valrubicin, radiotherapy, electromotive drug administration, vicinium, chemohyperthermia, photodynamic therapy, gene therapy, vaccine therapy and immunotherapy. For patients in whom BCG has once failed a repeat course of BCG or BCG plus interferon appears to be a reasonable practice. Likewise, single agent gemcitabine may be considered a treatment modality. However, after 2 or more BCG failures, especially in patients with earlier relapses or cancer persistence, single agent intravesical chemotherapy with valrubicin, gemcitabine or docetaxel appears to be less active than doublet/triplet intravesical chemotherapy or mitomycin chemothermotherapy. Gene therapy or conjugated antibodies may play a role upon further relapse. Single agent pembrolizumab is unlikely to be used as first line, but may be useful, along with multiple new immunotherapeutics, as part of a multimodal approach towards BCG unresponsive disease. CONCLUSIONS: Results from ongoing trials will provide us useful information about many of the existing regimens and probably new drugs will soon be available for this group of patients.