A Paradigm-Changing Idea in Muscle-Invasive Bladder Cancer: Is BCG Only for Early-Stage Disease?
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A New Immunotherapy Idea in Muscle-Invasive Bladder Cancer: Is BCG Not Just for Early-Stage Disease?
Could BCG Also Be an Immune-Priming Trigger in Muscle-Invasive Disease?
BCG has a very special place in the history of bladder cancer. For decades, it has been used as an effective intravesical immunotherapy, meaning treatment administered into the bladder, in non-muscle-invasive bladder cancer. However, BCG's conventional setting is NMIBC; standard treatment in muscle-invasive disease is systemic chemotherapy and radical surgery.
What distinguishes SAKK 06/19 is its consideration of BCG as more than a treatment for superficial bladder cancer: it is viewed as a priming intervention that could make the tumor microenvironment more immunologically active in muscle-invasive disease. The idea is that recombinant BCG administered into the bladder may increase local inflammation and antigen presentation, after which systemic chemotherapy and the PD-L1 inhibitor atezolizumab may produce a stronger local and systemic antitumor response.
Brief Concept Note: What Are MIBC, Intravesical Treatment and rBCG?
MIBCmeans muscle-invasive bladder cancer; the tumor has advanced into the muscle layer of the bladder wall. Intravesical treatmentmeans administering a drug directly into the bladder rather than intravenously. rBCGmeans recombinant BCG: a genetically modified form of BCG designed to strengthen the immune-stimulating properties of conventional BCG and improve its safety profile. The rBCG used in this study is also called VPM1002BC.
The Biological Rationale for This Combination
The bladder is a unique organ for intravesical treatment because an immune-stimulating agent can be administered directly into the cavity where the tumor develops. BCG activates innate and adaptive immune responses in the bladder wall. Chemotherapy may reduce tumor burden and induce immunogenic cell death. Atezolizumab blocks PD-L1, thereby reducing suppression of the T-cell response.
The hypothesis of SAKK 06/19 is that these three layers may complement one another: local immune activation, systemic cytotoxic treatment and immune checkpoint blockade. The study should therefore be interpreted as an attempt to reprogram the tumor microenvironment in bladder cancer, beyond simply trying the addition of a new drug.
Open-Label, Single-Arm Phase 2 SAKK 06/19 Study
SAKK 06/19 is an open-label, single-arm, multicenter phase 2 study conducted in patients with operable muscle-invasive bladder cancer. Patients with clinically staged cT2-T4a N0-1 MIBC were enrolled. They first received three weekly doses of intravesical rBCG, followed by perioperative chemo-immunotherapy with cisplatin + gemcitabine and atezolizumab. Radical cystectomy was then performed. Adjuvant atezolizumab was planned for patients with residual pathological ypT2 or higher or ypN+ disease.
1. Local immune priming
Intravesical rBCG was administered into the bladder on days 1, 8 and 15. The aim was to activate the local immune response.
2. Systemic treatment
Atezolizumab was administered every 3 weeks starting on day 1, and cisplatin + gemcitabine for 4 cycles starting on day 22.
3. Surgery and the adjuvant period
Radical cystectomy was performed after neoadjuvant treatment; adjuvant atezolizumab was planned in patients with high-risk residual disease.
Brief Concept Note: What Do Neoadjuvant, Adjuvant and Radical Cystectomy Mean?
Neoadjuvant treatmentis treatment given before surgery to shrink the tumor, suppress micrometastatic disease and increase the pathological response. Adjuvant treatmentis given after surgery to reduce the risk of recurrence. Radical cystectomyis the surgical removal of the bladder and surrounding lymph nodes; it is one of the most important curative treatment steps in muscle-invasive bladder cancer.
| Treatment step | Administration | Timing | Purpose | Clinical significance |
|---|---|---|---|---|
| Intravesical rBCG | Instillation of rBCG into the bladder | Days 1, 8, 15 | Local immune activation | The idea of preparing the immune microenvironment in the bladder wall for treatment. |
| Atezolizumab | PD-L1 inhibitor immunotherapy | Every 3 weeks from day 1 | Strengthening the T-cell response | Supporting the BCG-stimulated immune response with systemic checkpoint blockade. |
| Cisplatin + gemcitabine | Platinum-based neoadjuvant chemotherapy | 4 cycles from day 22 | Reducing tumor burden and suppressing micrometastatic disease | Combining the standard chemotherapy backbone with an immune strategy. |
| Radical cystectomy | Bladder and lymph node surgery | After neoadjuvant treatment | Assessing pathological response and providing curative local control | Critical endpoints such as pCR and PaR are measured in the surgical specimen. |
| Adjuvant atezolizumab | Continuation of immunotherapy in high-risk residual disease | In patients with ypT2 or higher or ypN+ disease | Reducing recurrence risk | An approach that adjusts treatment intensity according to pathological response. |
pCR %65: A Very Strong Pathological Response Signal for MIBC
The study enrolled 47 patients for treatment; central pathology assessment was possible for 40 patients. According to central assessment, pathological complete response was found in 26/40 patients, corresponding to a %65 pCR rate. Pathological response, meaning pCR or ypT1N0 or better response, was observed in 32/40 patients; this rate was %80 as reported.
Brief Concept Note: What Do pCR and PaR Mean?
pCRmeans pathological complete response: no remaining viable tumor or lymph node involvement in the surgical specimen, corresponding to ypT0 ypN0 in this study. PaRmeans pathological response: marked tumor regression with preoperative treatment and, in this study, downstaging to ypT1N0 or a better pathological stage. pCR generally indicates a deeper response, while PaR describes a broader group with a good response.
The Most Striking Aspect of These Data
- pCR %65: A strong signal markedly above historical pCR rates with cisplatin-based neoadjuvant chemotherapy in MIBC.
- PaR %80: Downstaging below the muscle-invasive level in a very large proportion of patients.
- EFS at 1 year %88: Event-free survival is promising with short follow-up.
- OS at 1 year %95: Early overall survival data are favorable, but long follow-up is necessary.
An Intensive but Feasible Combination
Treatment adherence in the study was notable. According to the visual summary, rBCG could be administered to %95 of patients, atezolizumab to %98, and %95 of patients completed 4 chemotherapy cycles. This is an important feasibility signal for a highly complex perioperative treatment.
Treatment-related adverse events were reported at an overall rate of %55; the rate of grade 3 or higher treatment-related adverse events was %48. Although any rBCG-related treatment-related adverse event appeared at a rate of %55, no grade 3 or higher rBCG-related adverse events were reported. The absence of reported treatment-related deaths is also important for safety.
Brief Concept Note: What Do TRAE and Grade 3 Mean?
TRAEmeans treatment-related adverse event. Grade 3generally indicates a severe but often manageable level of adverse event; hospitalization, intensive supportive care or a treatment delay may be needed. Grade 4 means life-threatening, while grade 5 means treatment-related death.
Truecheck Note: This Is a Single-Arm Phase 2 Study
SAKK 06/19 provides a very strong pathological response signal, but it is not a randomized phase 3 study. The %65 pCR rate should therefore not be directly interpreted as a new standard. Patient selection, clinical stage, central pathology assessment, treatment adherence and surgery rates can differ between studies. These data are a very promising, hypothesis-strengthening result that requires randomized confirmation.
SAKK 06/19 Along the Path From Conventional Neoadjuvant Chemotherapy to EV + Pembrolizumab
The pCR rate in MIBC is more than an academic number. Patients with a pathological complete response tend to have a lower long-term recurrence risk. Although pCR does not fully replace actual survival endpoints, it is therefore closely monitored as a strong early indicator of efficacy in neoadjuvant treatment.
Historically, pCR rates with platinum-based neoadjuvant chemotherapy regimens such as cisplatin/gemcitabine were reported at approximately %25–35 in most studies. More intensive dd-MVAC regimens produced higher pathological responses in some studies. In recent years, pCR rates have begun to exceed %50 with perioperative immunotherapy and antibody-drug conjugates. In this context, the %65 pCR in SAKK 06/19 is notable despite the single-arm design.
| Approach / study | Patient context | Treatment strategy | pCR / main response | Key result | Clinical interpretation |
|---|---|---|---|---|---|
| Conventional cisplatin-based neoadjuvant chemotherapy | Cisplatin-eligible MIBC | Cisplatin/gemcitabine or MVAC variants + radical cystectomy | Approximately %25–35 pCR in most series | Historical standard with proven survival benefit | Still the main reference, but response rates are limited and many patients cannot receive cisplatin. |
| dd-MVAC | Fit, cisplatin-eligible MIBC | Dose-dense MVAC + surgery | Higher pCR and a better PFS/OS signal than GC in some analyses | VESPER data supported the possibility of greater efficacy with dd-MVAC in the neoadjuvant setting | May be more intensive and toxic; appropriate patient selection is needed. |
| ABACUS | Cisplatin-ineligible MIBC or MIBC in patients unable to receive chemotherapy | Neoadjuvant atezolizumab | pCR %31 | Meaningful pathological response with single-agent immunotherapy | Demonstrated the biological activity of immunotherapy in the neoadjuvant setting. |
| NIAGARA | Cisplatin-eligible MIBC | Neoadjuvant gemcitabine/cisplatin + durvalumab, followed by surgery and adjuvant durvalumab | Approximately 10-point increase in pCR; significant improvement in EFS and OS | Phase 3 EFS and OS benefit with perioperative immunotherapy | A new standard candidate adding immunotherapy to the platinum-based neoadjuvant backbone. |
| KEYNOTE-B15 / EV-304 | Cisplatin-eligible MIBC | Perioperative enfortumab vedotin + pembrolizumab vs cisplatin/gemcitabine | pCR %55,8 vs %32,5 | EFS, OS and pCR improved significantly | A strong non-platinum targeted-immune combination against a platinum-based approach. |
| KEYNOTE-905 / EV-303 | Cisplatin-ineligible MIBC or MIBC in patients declining cisplatin | EV + pembrolizumab + surgery vs a surgery-based approach | pCR %57,1 vs %8,6 | EFS and OS improved significantly | Perioperative EV+pembrolizumab is becoming a very strong option in patients unable to receive cisplatin. |
| SAKK 06/19 | cT2-T4a N0-1 MIBC; single-arm phase 2 | Intravesical rBCG + cisplatin/gemcitabine + atezolizumab + surgery ± adjuvant atezolizumab | pCR %65; pCR/PaR %80 | EFS at 1 year %88; OS %95 | A very strong early signal combining local bladder immune activation with systemic chemo-immunotherapy. |
This Table Is Not a Direct Head-to-Head Comparison
Different studies have different patient populations, stage distributions, pathology assessment methods, surgery rates, follow-up durations and endpoints. It is therefore inappropriate to interpret pCR rates as a definitive answer to which treatment is better. In historical context, however, the %65 pCR and %80 PaR signal in SAKK 06/19 has a notable place among the high pathological response rates reported in MIBC to date.
Treatment in MIBC Is Now Directed at the Bladder Microenvironment as Well as Systemically
Major advances in perioperative treatment for MIBC in recent years have mostly come from systemic therapies: immune checkpoint inhibitors, antibody-drug conjugates and platinum-based combinations. SAKK 06/19 adds a local immune stimulant administered into the bladder to this systemic strategy.
This approach views bladder cancer not only as a systemic disease carrying a risk of distant micrometastases, but also as a disease whose local tumor microenvironment can be reprogrammed. If randomized studies confirm this idea, the treatment paradigm in MIBC may evolve beyond preoperative systemic treatment toward local + systemic immune synchronization.
Brief Concept Note: What Do Tumor Microenvironment and Immune Checkpoint Mean?
The tumor microenvironmentis the biological setting around cancer cells, consisting of immune cells, blood vessels, connective tissue, cytokines and other cellular interactions. An immune checkpoint inhibitoris a class of drugs that prevents cancer from applying brakes to the immune system. Atezolizumab is an immune checkpoint inhibitor targeting PD-L1.
How Should We Discuss This With a Patient?
“In this study, researchers combined a special BCG treatment administered into the bladder with intravenous chemotherapy and immunotherapy. The aim was to eliminate the tumor as deeply as possible before surgery. In the initial results, approximately two-thirds of patients had no viable tumor remaining in the surgical specimen. However, this is still a single-arm phase 2 study; larger randomized studies are needed before it can become standard treatment.”
Higher pCR Will Intensify the Question of Whether Radical Cystectomy Is Always Necessary
The potential long-term impact of SAKK 06/19 should be considered not only through its pCR rate, but also through its capacity to inspire bladder-preserving strategies. If a treatment can produce pathological complete responses at a very high rate in muscle-invasive bladder cancer, the idea of omitting or delaying radical cystectomy in selected patients may be investigated more seriously in the future.
However, the current message of this study is not to replace radical cystectomy with bladder preservation. The study's standard sequence includes surgery, and pCR is measured in the surgical specimen. Bladder preservation requires much stronger validation tools, including reliable clinical complete response criteria, imaging, cystoscopy, re-TURBT, urinary biomarkers, ctDNA and long-term follow-up.
Brief Concept Note: What Does a Bladder-Preserving Strategy Mean?
A bladder-preserving strategyis a treatment approach that aims to leave the bladder in place instead of radical cystectomy. This is generally done with trimodal treatment, namely TURBT + chemoradiotherapy. As pCR rates increase with new neoadjuvant therapies, omitting surgery in selected patients is being investigated, but this approach is not yet a general standard in MIBC.
Questions That Must Be Answered in the Future
- Randomized confirmation: Will rBCG + chemo-IO provide EFS and OS benefits over standard perioperative treatments?
- Durability of pCR: To what extent will the %65 pCR translate into long-term metastasis-free survival and overall survival?
- Patient selection: In which tumors does local immune activation with rBCG produce a stronger response?
- Biomarkers: Can PD-L1, TMB, tumor-infiltrating lymphocytes, urinary immune profiles or ctDNA responses improve patient selection?
- Bladder preservation: Could omitting cystectomy be safe in patients with high pCR or a clinical complete response?
- rBCG safety: Will severe rBCG-related toxicity truly remain low in larger studies?
Combining Local Immune Activation With Systemic Chemo-Immunotherapy
Academic Assessment
This study is very exciting because it shows that combining local immune activation with systemic chemo-immunotherapy in muscle-invasive bladder cancer may produce a strong pathological response signal.
The %65 pCR and %80 pathological response rates remind us to view neoadjuvant treatment in bladder cancer as more than tumor shrinkage: it can also be a strategy to reprogram the tumor microenvironment.
If confirmed by randomized studies, this approach could evolve into a new treatment paradigm in MIBC that is more sophisticated, supported by biomarkers and perhaps inspires bladder-preserving strategies in selected patients.
SAKK 06/19 Makes Intravesical Immune Priming a Serious Consideration in MIBC
The SAKK 06/19 study presented at ASCO 2026 shows that adding intravesical recombinant BCG to systemic chemo-immunotherapy in muscle-invasive bladder cancer may produce very high pathological response rates. Central assessment reported pCR of %65, pCR/PaR of %80, EFS at 1 year of %88 and OS at 1 year of %95. These results are particularly striking when compared with historical cisplatin-based neoadjuvant chemotherapy data.
However, the study has a single-arm phase 2 design. It would therefore be inappropriate to say that it has changed the standard today. Nevertheless, the results suggest that local immune activation in bladder cancer may be rationally combined with systemic treatments, potentially raising pCR rates beyond expected levels.
In the coming period, long-term EFS and OS results from SAKK 06/19, biomarker analyses and randomized confirmation studies should be followed closely. If this signal is confirmed, local-systemic combinations targeting the immune microenvironment of the organ containing the tumor, alongside stronger systemic therapies, may also become part of the search for new standards in MIBC.
References
- ASCO 2026 Abstract 4503. Intravesical recombinant BCG combined with chemo-immunotherapy as perioperative therapy for patients with muscle-invasive bladder cancer: Primary analysis of SAKK 06/19.
- Targeted Oncology. Intravesical Recombinant BCG Plus Chemoimmunotherapy Yields High pCR in MIBC. 2026.
- ClinicalTrials.gov. Intravesical Recombinant BCG Followed by Perioperative Chemo-Immunotherapy for Patients With MIBC. NCT04630730.
- Swiss Cancer Institute. SAKK 06/19: Neoadjuvant local immunotherapy plus atezolizumab in localized operable bladder cancer.
- Petrausch U et al. Novel sequential treatment strategy for patients with muscle-invasive bladder cancer: SAKK 06/19 protocol. BMJ Open. 2023.
- UroToday. ESMO 2025: Interim analysis of SAKK 06/19 study.
- The ASCO Post. KEYNOTE-B15/EV-304: Perioperative enfortumab vedotin plus pembrolizumab in cisplatin-eligible MIBC. 2026.
- ESMO Daily Reporter. KEYNOTE-905/EV-303: Perioperative enfortumab vedotin plus pembrolizumab in cisplatin-ineligible MIBC. 2025.
- Powles T et al. Perioperative Durvalumab with Neoadjuvant Chemotherapy in Operable Bladder Cancer. New England Journal of Medicine. 2024.
- Szabados B et al. Final results of neoadjuvant atezolizumab in cisplatin-ineligible patients with muscle-invasive bladder cancer: ABACUS. European Urology. 2022.
- Pfister C et al. VESPER trial: 5-year survival endpoints with dd-MVAC vs gemcitabine/cisplatin in MIBC. Lancet Oncology. 2024.
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