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Efficacy, Safety, and Certainty of Evidence for Systemic Antineoplastic Therapies in Treatment-resistant Adult Malignancies: A Systematic Review, Exploratory Meta-analysis, and Grade Assessment

This systematic review and exploratory meta-analysis of 18 randomized clinical trials (2021–2026) concludes that while selected systemic antineoplastic therapies offer clinically meaningful survival and response benefits for adults with treatment-resistant malignancies, high-certainty evidence is concentrated in specific therapeutic contexts and pooled estimates must be interpreted cautiously due to substantial heterogeneity.

Original authors: Mayky Sousa Rodrigues, Luid Alberto Silva, Carlos Eduardo de Moura Silva

Published 2026-07-07

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Mayky Sousa Rodrigues, Luid Alberto Silva, Carlos Eduardo de Moura Silva

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the human body as a bustling city, and cancer as a group of rebellious gangs that have taken over specific neighborhoods. For years, doctors have tried to evict these gangs using "systemic antineoplastic therapies"—think of these as specialized police forces, drones, or even custom-built robots sent in to stop the gangs from growing and spreading.

However, these gangs are tricky. They are like master shapeshifters. Sometimes, they ignore the police from the start (primary resistance). Other times, they pretend to surrender, only to regroup, change their uniforms, and attack again later (acquired resistance). This is what the paper calls "treatment-resistant" cancer.

Here is a simple breakdown of what this research team did and what they found, using everyday analogies.

The Mission: A "Big Data" Check-Up

The researchers didn't test new drugs themselves. Instead, they acted like detectives reviewing case files. They gathered 18 recent "case files" (randomized clinical trials published between 2021 and 2026) that tested these new police forces against the rebellious gangs in adults whose cancer had already fought back against previous treatments.

They looked at three main things:

Efficacy: Did the new strategy actually stop the gangs? (Did the city stay safe?)
Safety: Did the new strategy cause too much collateral damage to the city? (Did the police hurt innocent bystanders?)
Certainty: How sure are we that these results are real and not just a lucky guess?

The Big Findings: "It Depends on the Neighborhood"

The most important takeaway is that there is no "one-size-fits-all" solution. You can't just send the same police force to every neighborhood and expect the same result.

The Super-Performers (The "Elite Units")
The study found that for specific types of cancer-gangs, certain new therapies worked like magic. These are the "high-certainty" winners:

Cabozantinib: Worked like a heavy-duty lock on a specific type of thyroid cancer gang that had already ignored other locks.
CAR-T Cell Therapies (Ciltacabtagene and Axicabtagene): Imagine these as "living weapons" that reprogram the body's own immune cells to hunt down specific blood cancer gangs (lymphoma and multiple myeloma). They were incredibly effective at clearing the streets.
Antibody-Drug Conjugates (Sacituzumab and Enfortumab): Think of these as "smart missiles" that carry a bomb directly to the cancer cell without blowing up the whole neighborhood. They worked wonders for triple-negative breast cancer and bladder cancer.
Palbociclib: A maintenance tool that kept breast cancer at bay longer, though it required careful monitoring.

The Mixed Results (The "Struggling Units")
Not every new strategy was a home run. Some were like police cars that arrived but couldn't catch the gang.

Some drugs worked well for some patients but not others.
Some strategies (like certain tumor-treating fields or specific chemotherapy combos) showed promise in small groups but didn't clearly beat the standard treatment for the whole group.
In some cases, the new drug was no better than the old one, or the side effects were too high to justify the small gain.

The "Heterogeneity" Problem: Why We Can't Just Average It All

The researchers tried to combine all the results into one big average number (a meta-analysis) to see if, generally, these new drugs work better than old ones.

The Result: The average looked promising! The new drugs seemed to extend life and delay cancer growth.
The Catch: The data was like trying to average the speed of a snail, a race car, and a rocket ship. Because the cancer types and drugs were so different, the "average" is just a rough sketch, not a precise map. The researchers warned us not to take this average as a guarantee that every new drug works for every cancer. It's more like saying, "Some of these new tools work incredibly well, but you have to pick the right tool for the right job."

The Cost of Doing Business: Safety and Side Effects

Just because a weapon is powerful doesn't mean it's safe to use in a crowded city.

The Trade-off: The drugs that worked the best often came with the heaviest "collateral damage."
- The "living weapons" (CAR-T) caused intense immune reactions (fever, confusion) because they were so active.
- The "smart missiles" caused severe diarrhea and low blood counts.
- The "heavy-duty locks" (Cabozantinib) caused high blood pressure and skin issues.
The Lesson: High certainty of evidence doesn't just mean "this works." It also means "we are very sure this causes these specific side effects." Doctors have to weigh the benefit (stopping the gang) against the cost (hurting the city).

The Verdict: Precision Over Generalization

The paper concludes that we have made huge progress. We have found specific, powerful tools that can defeat cancer even when it has fought back before. However, the era of "one drug for all" is over.

The main message is:
If you have a specific type of resistant cancer, there is a good chance a specific, high-certainty therapy exists that can help you. But you can't assume that just because a new drug exists, it will work for everyone. The decision to use it depends on matching the right "key" to the right "lock," while being fully aware of the "price" (side effects) you have to pay.

The researchers are essentially saying: "We have better weapons now, but we must be smarter about which one we choose for which battle."

Technical Summary: Efficacy, Safety, and Certainty of Evidence for Systemic Antineoplastic Therapies in Treatment-Resistant Adult Malignancies

Problem Statement
Therapeutic resistance remains a primary driver of treatment failure, disease progression, and reduced survival in oncology. While systemic antineoplastic therapies have expanded significantly, the magnitude and certainty of their benefits in resistant, refractory, relapsed, or previously treated adult malignancies vary widely across tumor types and therapeutic classes. Resistance is a heterogeneous process involving clonal evolution, genomic instability, and microenvironmental interactions, yet it is not consistently defined or measured across randomized clinical trials (RCTs). Consequently, there is a need to synthesize contemporary evidence to determine which interventions provide clinically meaningful benefits with acceptable toxicity, moving beyond statistical significance to assess the actual certainty of the evidence.

Methodology
This study is a prospective systematic review, exploratory meta-analysis, and GRADE assessment registered in PROSPERO (CRD420261386007) and conducted according to PRISMA 2020 guidelines.

Search Strategy: A systematic search of PubMed/MEDLINE, Cochrane CENTRAL, SciELO, and Google Scholar was performed for RCTs published between 2021 and 2026.
Eligibility: The review included adult patients (≥18 years) with malignant tumors treated with systemic antineoplastic therapies (chemotherapy, immunotherapy, targeted therapy, antibody–drug conjugates, cellular therapy, etc.) in settings of treatment resistance, refractoriness, relapse, recurrence, or prior treatment failure.
Exclusion: Non-randomized studies, phase I trials, pediatric populations, and studies lacking sufficient outcome data were excluded.
Analysis:
- Risk of Bias: Assessed using the Cochrane RoB 2 tool.
- Certainty of Evidence: Evaluated using the GRADE approach (considering risk of bias, inconsistency, indirectness, imprecision, and publication bias).
- Meta-analysis: Exploratory random-effects meta-analyses were performed for time-to-event outcomes (Overall Survival [OS], Progression-Free Survival [PFS], Event-Free Survival [EFS]) where sufficient data existed. Heterogeneity was assessed using $I^2$ , $\tau^2$ , and the chi-square test.

Key Contributions

Synthesis of Contemporary Evidence: The review synthesizes data from 18 RCTs published between 2021 and 2026, covering a broad spectrum of solid and hematologic malignancies including breast cancer, urothelial carcinoma, thyroid cancer, lymphoma, multiple myeloma, and colorectal cancer.
GRADE Assessment: It provides a rigorous evaluation of the certainty of evidence, identifying 19 high-certainty outcomes. This distinguishes between interventions supported by robust phase III data and those relying on exploratory or indirect evidence.
Differentiation of Benefit and Harm: The study explicitly highlights that high-certainty evidence applies to both efficacy benefits and toxicity signals, emphasizing that certainty of evidence is not synonymous with certainty of benefit.
Contextualized Meta-analysis: Rather than presenting pooled estimates as uniform class effects, the authors interpret meta-analytic results cautiously, acknowledging substantial clinical and statistical heterogeneity across tumor types and therapeutic mechanisms.

Results

Included Studies: 18 RCTs were analyzed, evaluating therapies such as cabozantinib, ciltacabtagene autoleucel, axicabtagene ciloleucel, sacituzumab govitecan, palbociclib, and enfortumab vedotin.
Efficacy Findings:
- Strongest Evidence: The most robust efficacy signals were observed for:
  - Cabozantinib: Significant PFS benefit in radioiodine-refractory differentiated thyroid cancer (HR 0.22).
  - Ciltacabtagene autoleucel: Substantial PFS and response benefits in lenalidomide-refractory multiple myeloma (HR 0.26).
  - Axicabtagene ciloleucel: Improved EFS, PFS, and response in early relapsed/refractory large B-cell lymphoma (HR 0.40).
  - Sacituzumab govitecan: Improved PFS and OS in metastatic triple-negative breast cancer (PFS HR 0.41; OS HR 0.48).
  - Enfortumab vedotin: Improved OS and PFS in previously treated urothelial carcinoma (OS HR 0.70).
  - Palbociclib: Improved PFS in hormone receptor-positive/HER2-positive advanced breast cancer, though with increased toxicity.
- Modest/Null Findings: Several interventions showed modest, mixed, or absent efficacy, including ripretinib in gastrointestinal stromal tumors, tumor treating fields in ovarian cancer, and tisagenlecleucel in aggressive B-cell lymphoma compared to standard salvage therapy.
Meta-analysis:
- PFS: The pooled HR was 0.56 (95% CI 0.37–0.83), indicating a statistically significant improvement. However, heterogeneity was very high ( $I^2 = 94\%$ ).
- OS: The pooled HR was 0.72 (95% CI 0.62–0.84), also statistically significant, with moderate to substantial heterogeneity ( $I^2 = 55\%$ ).
- Interpretation: Due to high heterogeneity, these pooled estimates are considered exploratory and hypothesis-generating rather than evidence of a uniform class effect.
Safety: Significant toxicity was associated with several high-efficacy therapies. CAR-T therapies (axi-cel, cilta-cel) showed high rates of immune-mediated toxicities (cytokine release syndrome, neurotoxicity). Sacituzumab govitecan and palbociclib were associated with increased hematologic and gastrointestinal toxicities. Cabozantinib increased grade 3/4 adverse events significantly.
Certainty of Evidence: 19 outcomes were rated as high certainty, concentrated in the six therapeutic contexts mentioned above. These included PFS, OS, objective response, and specific toxicity profiles (e.g., grade 3 diarrhea, hematologic toxicity).

Significance and Claims
The paper claims that selected systemic antineoplastic therapies can provide clinically meaningful benefits in treatment-resistant adult malignancies, but these benefits are not uniformly distributed. The primary significance lies in the identification of specific therapeutic contexts where high-certainty evidence supports the use of these agents (e.g., cabozantinib in thyroid cancer, CAR-T in specific lymphomas/myeloma).

The authors emphasize that:

Resistance is not futility: Biologically rational strategies can overcome resistance in specific settings, but therapeutic innovation alone does not guarantee benefit.
Heterogeneity is critical: Broad pooled estimates across resistant malignancies are useful only as exploratory summaries; clinical decisions must be grounded in disease-specific and therapy-specific evidence.
Certainty includes harm: High-certainty evidence regarding toxicity is as crucial for decision-making as evidence of survival benefit.
Decision-making framework: Treatment decisions should integrate survival benefit, tumor response, adverse events, risk of bias, and the certainty of evidence, rather than relying solely on statistical significance or the presence of an experimental therapy.

The study concludes that while systemic therapies can meaningfully improve outcomes in resistant settings, the most reliable evidence is concentrated in specific contexts, and future research requires clearer definitions of resistance and biomarker-driven analyses to better identify patient populations likely to benefit.