Bladder cancer originates in the cells lining the bladder, a hollow organ in the lower abdomen that stores urine. Immunotherapy represents a modern approach to cancer treatment, distinct from traditional methods like chemotherapy or radiation. This therapy functions by empowering the body’s natural defense system, the immune system, to recognize and eliminate cancer cells.
Understanding Immunotherapy for Bladder Cancer
Immunotherapy for bladder cancer primarily involves two main strategies, depending on the disease stage. For non-muscle invasive bladder cancer (NMIBC), Bacillus Calmette-Guérin (BCG) is a common treatment. BCG is a weakened form of bacteria that, when introduced into the bladder, provokes a localized immune response, helping to destroy cancer cells lining the bladder.
For more advanced or metastatic bladder cancer, a different class of drugs called checkpoint inhibitors is often used. These medications, such as pembrolizumab, atezolizumab, nivolumab, durvalumab, and avelumab, work by blocking specific proteins on immune cells or cancer cells. By inhibiting these “checkpoints,” the drugs release the brakes on the immune system, allowing T-cells to more effectively recognize and destroy cancer cells.
Measuring Treatment Success
One common metric is the response rate, which indicates the percentage of patients whose cancer either shrinks significantly or disappears entirely. This rate is further categorized into a complete response (CR), meaning no detectable cancer remains, or a partial response (PR), where the tumor size decreases by a specified percentage. These measures reflect the immediate impact of the treatment on the tumor burden.
Another important measure is progression-free survival (PFS), which quantifies the duration a patient lives with the disease without it worsening. PFS is a valuable indicator of treatment effectiveness in controlling cancer growth. The ultimate measure of treatment success is overall survival (OS), representing the total length of time patients remain alive from the start of diagnosis or treatment.
Immunotherapy Success Rates by Bladder Cancer Stage
For high-risk NMIBC, BCG achieves a complete response rate in approximately 70% of patients after initial induction therapy. However, about 30-50% of these patients may experience recurrence or progression within five years, even with maintenance therapy. If BCG treatment fails, alternative immunotherapies like pembrolizumab have shown promise, with a complete response rate of around 40.6% in patients with BCG-unresponsive high-risk NMIBC.
In muscle-invasive bladder cancer (MIBC), immunotherapy with checkpoint inhibitors can be used in different settings. When administered before surgery (neoadjuvant), these therapies can reduce tumor size, potentially improving surgical outcomes. After surgery (adjuvant therapy), pembrolizumab has been shown to improve disease-free survival, with a 23% reduction in the risk of recurrence or death compared to observation in high-risk patients.
For metastatic bladder cancer, where the disease has spread beyond the bladder, checkpoint inhibitors are a standard treatment. In patients who have previously received chemotherapy, pembrolizumab achieved an overall response rate of 21.1%, with a median overall survival of 10.3 months. For patients who are not eligible for cisplatin-based chemotherapy, checkpoint inhibitors like pembrolizumab or atezolizumab can be frontline options, with response rates ranging from 23% to 29% and median overall survival between 10 to 15 months.
Factors Influencing Outcomes
The specific type of immunotherapy agent used plays a role, as different drugs target distinct immune pathways and may have varying efficacy profiles. A patient’s overall health status, often assessed by performance scores, can also affect their tolerance to treatment and subsequent response.
Prior treatments received, such as chemotherapy or radiation, can influence how effectively the immune system responds to subsequent immunotherapy. Tumor characteristics, like the expression level of PD-L1 (Programmed Death-Ligand 1) on cancer cells, can sometimes predict a better response to checkpoint inhibitors, though it is not a perfect biomarker. The presence of certain side effects might also correlate with treatment effectiveness in some cases, indicating an active immune response.