Intravesical combination therapies for non-muscle invasive bladder cancer: Recent advances and future directions

Bladder cancer is the 10th most frequently diagnosed cancer worldwide with 5-year survival rate around 70%. The current first-line treatment for non-muscle invasive bladder cancer is transurethral resection of bladder tumours followed by intravesical Mycobacterium Bovis Bacillus Calmette-Guérin (BCG) immunotherapy. However, tumor recurrence rate is still high ranging from 31% to 78% within five years. To avoid radical cystectomy, intravesical combination therapies have been developed as salvage treatments to overcome BCG failure. Recent advances in diagnostics thanks to tumor molecular profiling and in treatment such as development of immunotherapies provides more treatment options beyond BCG treatment. This also goes hand-in hand with formulation advances to deliver these new therapies where traditional drug delivery systems might not be suitable, which in turn is completed by challenges to deliver drugs via the intravesical route. In this article the aim was to provide an in-depth analysis of the current developments of intravesical combination therapies, ranging from relatively simple combinations of mixing existed intravesical therapeutic agents (immunotherapies and chemotherapies) to the combined formulations containing advanced gene therapies and targeted therapies, with special focus on therapies that have made it to the clinical trial stage. In addition, recent attempts to utilize device-assisted treatments and novel drug delivery platforms are included. This review also highlights the limitations that still need to be overcome such as the inadequate studies on newly explored drug carriers and proposes potential directions for future work to overcome BCG-failure.