What challenges did early RNA-based research face?

RNA is chemically unstable compared to DNA, posing significant technical hurdles in experiments to prevent degradation. Special laboratory methods, such as immediate sample preservation and cold room procedures, were necessary to maintain RNA integrity.

Why did Max Diehn choose radiation oncology?

He was drawn to radiation oncology because it allowed more time with patients, had significant technological aspects (imaging and precise radiation delivery), and presented an opportunity to make a difference in a field where molecular-level laboratory work was less prevalent compared to medical oncology.

How did the field of liquid biopsies become Max Diehn's focus?

Diehn initially saw an unmet clinical need in lung cancer patients—the inability to predict recurrence after treatment. He was inspired by prenatal diagnostics using cell-free DNA in pregnant women's blood and decided to pursue a similar approach for cancer detection.

What are the limitations of traditional imaging for detecting early cancer?

Traditional imaging methods like CT scans can generally detect tumors no smaller than 8-10mm, which already corresponds to about a billion cancer cells. This 'blind spot' between zero and a billion cells means early, microscopic metastatic disease is often undetectable, making treatment less effective.

Why are protein biomarkers like PSA, CEA, and CA19-9 limited for cancer screening?

These protein biomarkers lack specificity because normal cells can also produce them, albeit often at lower levels. This means it's hard to distinguish between low levels of cancer and normal physiological production, leading to many false positives and making them unsuitable for broad screening.

How do sensitivity and specificity impact cancer diagnostic tests?

Sensitivity (true positive rate) measures how often a test correctly identifies those with cancer, while specificity (true negative rate) measures how often it correctly identifies those without cancer. Achieving high levels in both is difficult, as pushing one often compromises the other, making a test with 100% sensitivity or specificity alone clinically useless.

What is the role of low-dose CT (LDCT) in lung cancer screening?

LDCT has been proven in the National Lung Screening Trial to significantly reduce lung cancer deaths. However, it's not perfect, can have false positives, and the absolute risk reduction is small (0.5-1%). Despite its benefits, many eligible patients still do not undergo screening.

How is cell-free DNA (cfDNA) used to detect cancer?

Cell-free DNA refers to short DNA fragments circulating in blood plasma. Cancer detection focuses on identifying specific mutations in these fragments (circulating tumor DNA or ctDNA) that are unique to cancer cells. These mutations serve as highly specific markers for the presence of cancer.

What is the difference between cell-free DNA (cfDNA) and circulating tumor DNA (ctDNA)?

Cell-free DNA (cfDNA) is the total DNA in circulation, encompassing DNA from both healthy and cancerous cells. Circulating tumor DNA (ctDNA) is a sub-fraction of cfDNA specifically derived from tumor cells, used as a specific cancer biomarker.

What is the utility of DNA methylation in liquid biopsies for cancer?

DNA methylation patterns refer to chemical modifications on DNA molecules that vary by tissue type and can influence gene activity. These patterns can help identify the tissue of origin for cancer DNA, which is particularly useful for initial screening to pinpoint the primary tumor location.

What are the limitations of pan-cancer screening tests like Grail for early detection?

Current pan-cancer screening tests have limited sensitivity for early-stage cancers (e.g., <5% for Stage 1 lung cancer in some data). Even with high specificity, in a low-prevalence population, the positive predictive value remains low, leading to a high rate of false positives and potential patient anxiety without clear clinical benefit.

How can liquid biopsies guide adjuvant therapy for minimal residual disease (MRD)?

Highly sensitive ctDNA tests can detect minimal residual disease (microscopic cancer cells remaining after initial treatment). If ctDNA is positive, indicating MRD, patients can immediately receive adjuvant therapies (like immunotherapy) at the point of lowest tumor burden and heterogeneity, significantly improving the chances of a cure.

What is the 'holy grail' for future liquid biopsy screening?

The ideal future is a blood test that, for every person, can detect any cancer (yes/no), identify its organ of origin, and enable early treatment, ideally months or years before it's clinically detectable by imaging. This will likely involve a combination of mutation analysis, methylation patterns, and fragmentomics, integrated with machine learning.

What is the current regulatory landscape for liquid biopsies in the US?

In the US, tests can be either FDA-approved or offered through CLIA-compliant labs. FDA approval is a rigorous process, while CLIA compliance regulates the lab itself, allowing companies to offer tests (like Grail) to patients and providers without specific FDA product approval, making it easier to bring new assays to market.

Key Moments

213 ‒ Liquid biopsies and cancer detection | Max Diehn, M.D. Ph.D.

Q: What is Max Diehn's background and how did he get into oncology research?

Max Diehn started in the MD PhD program at Stanford, doing his dissertation with Patrick Brown, inventor of DNA microarrays, focusing on immunology and oncology. His father's lymphoma diagnosis during college strongly influenced his decision to become a physician-scientist in oncology to improve treatments.

Peter Attia MD

Science & Technology3 min read147 min video

Jul 11, 2022|9,589 views|185|9

Save to Pod

Key Moments

TL;DR

Liquid biopsies using cell-free DNA show promise for early cancer detection and monitoring, but challenges remain.

Key Insights

Liquid biopsies detect circulating tumor DNA (ctDNA) in blood, offering a less invasive alternative to tissue biopsies.

Early research focused on protein biomarkers (like PSA) showed limited specificity, hindering clinical utility.

Circulating tumor cells (CTCs) were explored but faced challenges with abundance, specificity, and technical complexity.

Cell-free DNA (cfDNA) analysis, particularly by looking for cancer-specific mutations, shows significant potential for detection.

Next-generation sequencing (NGS) enables highly sensitive detection of cfDNA mutations, advancing liquid biopsy capabilities.

While promising, current liquid biopsy tests for early-stage cancer detection or screening have limitations in sensitivity and specificity compared to established methods.

FROM ACADEMIC ROOTS TO CLINICAL ASPIRATIONS

Dr. Max Diehn's journey into liquid biopsies began during his MD-PhD at Stanford, influenced by groundbreaking technologies like DNA microarrays from Pat Brown's lab. Initially exploring immunology and oncology, his dissertation work highlighted the challenges of RNA stability and the potential of cataloging gene expression. This foundational research, coupled with his later clinical focus on lung cancer, fueled a desire to address unmet clinical needs, particularly the inability to predict recurrence in early-stage lung cancer patients.

ADDRESSING THE DETECTION BLIND SPOT

A significant clinical frustration for Dr. Diehn was the limitation of traditional imaging (like CT scans) in detecting tumors smaller than 1 cm, representing billions of cells. This 'detection blind spot' extends to micrometastatic disease, which is undetectable yet can lead to recurrence and patient death. This gap motivated the exploration of blood-based biomarkers that could capture signals from widespread microscopic disease, providing a more sensitive and comprehensive view of cancer presence.

THE EVOLUTION OF LIQUID BIOPSY APPROACHES

The pursuit of liquid biopsies evolved through several stages. Early attempts focused on protein biomarkers like PSA, which suffered from low specificity due to normal cells also producing these proteins. Subsequently, circulating tumor cells (CTCs) were investigated but proved difficult to isolate in sufficient numbers and specificity, with healthy individuals sometimes yielding false-positive signals. These challenges paved the way for exploring cell-free DNA (cfDNA).

CELL-FREE DNA: A PROMISING NEW FRONTIER

Cell-free DNA (cfDNA), small DNA fragments found in blood plasma, emerged as a compelling biomarker. Inspired by its use in prenatal diagnostics, researchers hypothesized that cfDNA could carry tumor-derived DNA carrying cancer-specific mutations. This DNA, often around 170 base pairs and protected by histones, originates from various tissues, with a significant portion in healthy individuals derived from white blood cells. The key is identifying the subset of cfDNA that originates from cancer cells.

LEVERAGING GENETIC MUTATIONS FOR DETECTION

The core advantage of cfDNA in cancer detection lies in its mutations. Cancer arises and progresses through accumulated DNA mutations, which are generally absent in a patient's normal cells. By using highly sensitive next-generation sequencing (NGS), researchers can detect these specific tumor mutations within the cfDNA pool. Early strategies involved sequencing known tumor mutations, significantly increasing sensitivity and specificity compared to previous methods, addressing the challenge of low tumor DNA fractions.

ADVANCEMENTS AND FUTURE DIRECTIONS IN cfDNA ANALYSIS

The field has seen dramatic improvements, with techniques now achieving sensitivities of one in a million cfDNA molecules. Approaches are expanding beyond just mutations to include cfRNA and DNA methylation patterns, offering complementary information. While challenges remain in achieving high sensitivity and specificity for early-stage cancer screening, particularly for cancers like breast and prostate with lower cfDNA shedding, ongoing research into multi-analyte approaches and machine learning holds promise for improved diagnostic capabilities and eventual clinical utility, especially in guiding adjuvant therapy decisions and monitoring for minimal residual disease.

Mentioned in This Episode

●Software & Apps

●Companies

●Organizations

●Studies Cited

●Concepts

●People Referenced

Common Questions

Max Diehn started in the MD PhD program at Stanford, doing his dissertation with Patrick Brown, inventor of DNA microarrays, focusing on immunology and oncology. His father's lymphoma diagnosis during college strongly influenced his decision to become a physician-scientist in oncology to improve treatments.

Topics

Technology & Innovation Science & Mathematics Liquid Biopsies Cancer Detection Early Cancer Screening Medicine & Clinical Precision Oncology Molecular Diagnostics Radiation Oncology

Mentioned in this video

Concepts

MD PhD Program

A program for aspiring physician-scientists to combine medical and doctoral training.

p53

A tumor suppressor gene, often mutated in various cancers, but not always a 'driver' mutation.

PD-L1

A marker expressed in tumor cells that can hide cancer from the immune system, important for immunotherapy, measurable via RNA expression not DNA mutation.

Lung-CLiP

A mutation-based lung cancer screening method developed by Max Diehn's lab using ctDNA, integrating features like mutation type, fragment length, and smoking status with machine learning.

T-cell

A type of white blood cell, lymphocyte, critical for the adaptive immune system, studied by Diehn for gene expression changes upon activation.

Endoplasmic reticulum

An organelle inside cells where RNAs for secreted and surface proteins go, which Max Diehn developed a method to isolate.

Medical oncology

A medical specialty focused on the systemic treatment of cancer with drugs, initially considered by Max Diehn due to his father's experience.

Thy-1

Max Diehn's wife's name is Jenny.

Hodgkin's disease

A type of lymphoma that Henry Kaplan played a major role in curing with radiotherapy in the 1950s.

Prostate-specific antigen

A protein biomarker historically used for prostate cancer screening and follow-up, but with limitations in specificity.

Carcinoembryonic antigen

A protein biomarker historically used in cancer, sometimes elevated in lung cancer but with specificity issues.

CA 19-9

A protein biomarker historically used in cancer, noted for limitations in specificity.

Circulating tumor cell

Intact cancer cells that circulate in the blood, an early focus of liquid biopsy, but difficult to measure reliably due to low abundance and processing challenges.

Software & Apps

Low-dose computed tomography

A screening technique for lung cancer that has been shown to reduce mortality, but has limitations in resolution and potential for false positives.

DNA microarray

A revolutionary technology invented by Patrick Brown for measuring the expression of thousands of genes simultaneously.

Quantitative polymerase chain reaction

An enzymatic method used to amplify and quantify DNA, more complex than simple dye-based methods but used in specific situations.

Next-generation sequencing

High-throughput molecular methods for sequencing DNA, used to identify exact base sequences of millions of molecules in parallel.

Products

Grail

A diagnostic company using methylation patterns of cell-free DNA for pan-cancer screening, still in the CLIA environment and not FDA approved for screening.

Companies

Natera

A company with Medicare-approved ctDNA tests for colorectal cancer, used for minimal residual disease detection.

Impossible Foods

A company founded by Patrick Brown, Max Diehn's former PhD advisor.

Guardant Health

One of the first companies in the liquid biopsy field, with an FDA-approved test used for genotyping advanced metastatic cancer patients to guide treatment decisions.

Organizations

Stanford University

Max Diehn and Peter Attia attended medical school at Stanford University, and Diehn also did his PhD and residency training there, eventually joining the faculty.

Food and Drug Administration

The US agency that approves diagnostic tests and drugs, with a more rigorous approval process than CLIA compliance.

National Cancer Institute

A component of the NIH, showing significant interest and increased funding for liquid biopsy research.

National Institutes of Health

The primary federal agency for biomedical research, funding a significant and increasing amount of liquid biopsy research.

People

Patrick Brown

Max Diehn's PhD advisor at Stanford, known for inventing DNA microarrays. He later founded Impossible Foods.

Howard Chang

A former postdoc in Pat Brown's lab who led early work on long non-coding RNAs, now a professor at Stanford.

Henry Kaplan

The first chairman of radiation oncology at Stanford, a famous radiation oncologist and physician-scientist who cured Hodgkin's disease with radiotherapy.

Dennis Lo

A researcher in Hong Kong who led early work on prenatal diagnostics using cell-free DNA.

Stephen Quake

A researcher at Stanford who led early work on prenatal diagnostics using cell-free DNA.

Studies & Research

National Lung Screening Trial

A landmark study that proved low-dose CT scans could significantly reduce lung cancer deaths in high-risk individuals.

DNA methylation

A chemical modification of DNA molecules that can influence gene expression and serve as exquisite marks of tissue origin, used in some liquid biopsies.

Legislation & Policy

Clinical Laboratory Improvement Amendments

An act of Congress that regulates laboratories performing diagnostic tests, allowing assays to be used on patients without full FDA approval if the lab is compliant.