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#181 - Robert Gatenby, M.D.: Viewing cancer through an evolutionary lens and why this offers a radically different approach to treatment

Oct 25, 2021 1h 59m 32 insights
<p><span style="color: #000000;">Robert (Bob) Gatenby is a radiologist who specializes in exploring theoretical and experimental models of evolutionary dynamics in cancer and cancer drug resistance. He has developed an adaptive therapy approach for treating cancer which has shown promise in improving survival times with less cumulative drug use. In this episode, Bob explains what brought him into medicine, his search for organizing principles from which to understand cancer, and the mathematical modeling of other complex systems that led him to model the dynamics of tumor cell changes in cancer. He discusses his pilot clinical trial treating metastatic prostate cancer, in which he used an evolutionary game theory model to analyze patient-specific tumor dynamics and determine the on/off cycling of treatment. He describes how altering chemotherapy to maximize the fitness ratio between drug-sensitive and drug-resistant cancer cells can increase patient survival and explains how treatment of metastatic cancer may be improved using adaptive therapy and strategic sequencing of different chemotherapy drugs.</span><span style="color: #333333;"><br /> <br /></span><span style="color: #000000;">We discuss:</span><span style="color: #333333;"><br /></span></p> <ul> <li><span style="color: #000000;">Bob's unlikely path to medicine and disappointment with his medical school experience [1:45];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Rethinking the approach to cancer: using first principles and applying mathematical models [12:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Relating predator-prey models to cancer [26:30];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Insights into cancer gathered from ecological models of pests and pesticides [32:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Bob's pilot clinical trial: the advantages of adaptive therapy compared to standard prostate cancer treatment [41:45];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">New avenues of cancer therapy: utilizing drug-sensitive cancer cells to control drug-resistant cancer cells [48:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">The vulnerability of small populations of cancer cells and the problem with a "single strike" treatment approach [56:00];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Using a sequence of therapies to make cancer cells more susceptible to targeted treatment [1:05:00];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">How immunotherapy fits into the cancer treatment toolkit [1:15:30];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Why cancer spreads, where it metastasizes, and the source-sync trade off [1:20:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Defining Eco- and Evo-indices and how they can be used to make better clinical decisions [1:29:45];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Advantages of early screening for cancer [1:40:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Bob's goals for follow-ups after the success of his prostate cancer trial [1:42:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">Treatment options for cancer patients who have "failed therapy" [1:51:15];</span><span style="color: #333333;"><br /></span></li> <li><span style="color: #000000;">More.</span><span style="color: #333333;"><br /></span></li> </ul> <p>Learn more: https://peterattiamd.com/</p> <p>Show notes page for this episode: <span style="color: #333333;"><a href="https://peterattiamd.com/RobertGatenby">https://peterattiamd.com/RobertGatenby</a></span></p> <p>Subscribe to receive exclusive subscriber-only content: https://peterattiamd.com/subscribe/</p> <p>Sign up to receive Peter's email newsletter: https://peterattiamd.com/newsletter/</p> <p>Connect with Peter on Facebook | Twitter | Instagram.</p>
Actionable Insights

1. Adaptive Cancer Therapy

Instead of continuous maximum tolerated dose, apply just enough therapy to reduce the cancer population to a manageable level, then reduce or withdraw treatment to allow sensitive cells to outcompete resistant ones, preventing the selection and proliferation of highly resistant strains.

2. Post-Remission Extinction Strategy

After initial effective therapy reduces cancer to very small or undetectable levels, do not continue the same treatment. Instead, apply a sequence of different, smaller perturbations to exploit the vulnerability of the remaining small, resistant population and drive it to extinction.

3. Leverage Sensitive Cells

Recognize that sensitive cancer cells, when therapy is withdrawn, can actively outcompete and even destroy resistant cancer cells due to their fitness advantage, rather than merely controlling them.

4. Sequence Therapies Strategically

Sequence different therapies rather than administering them all at once, as this allows you to exploit the fitness cost of resistance mechanisms. As the tumor population shrinks and fragments, it becomes more vulnerable to subsequent, subtle perturbations.

5. Target Fragmented Tumors

When therapies reduce large cancers to small, fragmented, and undetectable populations (e.g., after neoadjuvant therapy), this is the optimal time to intensify treatment and aim for eradication, as these small, isolated groups are highly vulnerable due to stochasticity and Allee effects.

6. Immunotherapy as Closer

Consider immunotherapy as a ‘closer’ in cancer treatment, most effectively deployed when the tumor population is already small and fragmented (e.g., after initial debulking therapies), as Allee effects make small populations more vulnerable to immune response.

7. Optimize Existing Cancer Drugs

Instead of solely focusing on developing new cancer drugs, prioritize rethinking and optimizing the strategic use of existing, older drugs, as current approaches often fail to leverage their full potential in an evolutionarily informed manner.

8. Avoid Continuous ADT

For metastatic prostate cancer, once PSA normalizes or becomes undetectable with androgen deprivation therapy (ADT), avoid continuous ADT due to its severe metabolic side effects. Instead, apply additional, different therapies to prevent resistance and aim for extinction.

9. Prostate Cancer Adaptive Protocol

For prostate cancer, administer treatment until the tumor shrinks to 50% of its pre-treatment value, then withdraw the drug. Allow the tumor to grow back, leveraging the fitness advantage of sensitive cells in the absence of treatment to outcompete resistant cells.

10. Pediatric Oncology Multi-Drug Strategy

Emulate pediatric oncology’s successful leukemia treatment strategy: follow initial induction therapy with immediate, sequential application of different drug groups, even when no apparent tumor remains, to prevent relapse and achieve cure.

11. Optimize Antibiotic Use

Question the practice of prolonged antibiotic courses (e.g., 10 days when symptoms resolve in 3) as this may contribute to antibiotic resistance by selecting for resistant bacteria; consider adaptive approaches to keep resistant populations low.

12. Challenge Medical Dogma

Be willing to question established medical dogma and consider alternative approaches, especially in areas where current methods have shown limited success, as the medical community can be very conservative and resistant to change.

13. Recognize Non-Linearity

When dealing with complex systems, recognize that human intuition often struggles with non-linear dynamics and feedback loops. Seek to understand first principles and underlying mathematics rather than relying solely on intuition.

14. Embrace Humility

When facing complex problems, especially in fields like medicine, cultivate humility and be willing to consult mathematical models and computer simulations, as human intuition and confidence can be insufficient without them.

15. Iterative Problem Solving

For highly complex and chaotic systems like cancer, focus on short-term predictions and interventions (e.g., next 3 months), gathering new data, and recalibrating models for subsequent steps, rather than attempting to predict the entire long-term course.

16. Prioritize Early Cancer Screening

Given that smaller cancer populations are more vulnerable to extinction and have less genetic diversity, prioritize early cancer screening to detect tumors when they are most susceptible to treatment.

17. Gather Cancer Ecological Data

To better understand and treat cancer, collect fundamental eco-evolutionary data such as birth rates, death rates, and nutrient cycles (carbon, iron, nitrogen) of cancer cell populations, similar to how ecologists study ecosystems.

18. Require Cancer Drug Resistance Plans

Advocate for cancer drug development and approval processes to include mandatory resistance management plans, requiring identification of resistance mechanisms and strategies to prevent them, similar to regulations for pesticide manufacturers.

19. Target Resistance’s Weakness

Design therapy sequences to anticipate how cancer will evolve resistance, then attack the specific ‘Achilles heel’ or vulnerability that is exposed by that particular resistance strategy.

20. Chemo-Immuno Sequence

Explore sequencing chemotherapy before immunotherapy, as evidence suggests that cancer cells surviving chemotherapy may become more vulnerable to immune-based treatments.

21. Add Environmental Perturbations

Beyond drugs, consider adding environmental or metabolic perturbations (e.g., anti-angiogenics to reduce blood flow, antacids, or other metabolic interventions) in combination with drug therapies to create a more difficult environment for cancer cells.

22. Prioritize Phenotype-Environment

When studying cancer evolution, prioritize understanding the morphological matching of cell phenotype to its environment and the environmental selection forces, rather than solely focusing on genetic mutations, as genes are often consequences, not causes, of evolution.

23. Utilize Imaging for Evolution

Employ non-destructive imaging techniques (radiologic studies) to monitor intratumoral evolution over time, aiming to bridge macroscopic images with microscopic cellular and molecular changes to understand how cancer adapts during therapy.

24. Landscape Ecology for Cancer

Adapt landscape ecology techniques to cancer imaging by identifying distinct ‘habitats’ within tumors from macroscopic images, then extrapolating cellular and molecular dynamics from these defined areas to understand intratumoral evolution.

25. Interpret Liquid Biopsy Carefully

When using circulating tumor DNA or cells, carefully consider their origin and representativeness of the entire tumor population, as they may primarily reflect less fit, dying cells (losers in the evolutionary game) rather than the most aggressive, resistant ones.

26. Caution with In Vitro Data

Exercise caution when extrapolating results from in vitro cancer studies (e.g., cells grown in a dish) to in vivo patient outcomes, as the environmental selection forces and evolutionary pressures are vastly different in a lab setting.

27. Find Open-Minded Oncologists

If considering adaptive or evolution-based cancer therapies, seek out oncologists who are brave and willing to go against conventional dogma, as these approaches require swimming against the mainstream medical current.

28. Discuss Adaptive Therapy

If you or a loved one are facing limited cancer treatment options, discuss the possibility of adaptive or evolution-based therapies with your oncologist, recognizing that finding a willing physician may be challenging due to non-standard practice concerns.

29. Adaptive Therapy for Cancers

Consider applying adaptive and extinction-based therapies to cancers that respond extremely well to initial treatment, such as ovarian cancer, small cell lung cancer, and initial metastatic prostate cancer, as these are ’low-hanging fruit’ for potential eradication.

30. Novel GBM Treatment Sequences

Consider exploring unconventional treatment sequences for glioblastoma, such as radiation therapy before surgery, to study how cells evolve resistance during radiation and potentially inform more effective strategies, despite current medical reluctance.

31. Rethink Pancreatic Fibrosis

Re-evaluate the role of fibrosis in pancreatic cancer; if it’s a host response rather than a tumor adaptive strategy, promoting fibroblasts might be beneficial by increasing competition for space and potentially killing off tumor cells, contrary to current approaches.

32. Deepen Health Knowledge

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