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Curious Dr. George | Plumbing the Core and Nibbling at the Margins of Cancer

How Can Detection of Tumor DNA in the Blood Aid Advanced Cancer Treatment?

Curious Dr. George
Cancer Commons Contributing Editor George Lundberg, MD, is the face and curator of this invitation-only column.

Paul Billings, MD, PhD
Chief Medical Officer at Natera

Alexey Aleshin, MD, MBA
VP Medical Affairs, Oncology, at Natera

 

As a tumor grows, it may shed fragments of its DNA into the patient’s bloodstream. After treatment, if part of the tumor remains or it begins to grow again, more of this circulating tumor DNA (ctDNA) may enter the blood. That raises the possibility that detecting ctDNA could help clinicians monitor molecular or minimal residual disease—cancer that remains after treatment and cannot be detected by traditional imaging methods.

Here, our Curious Dr. George talks ctDNA with two leaders at Natera, a company that develops ctDNA tests: Chief Medical Officer Paul Billings, MD, PhD, and VP Medical Affairs, Oncology, Alexey Aleshin, MD, MBA.

Curious Dr. George: When initially diagnosed, potentially lethal cancers found at advanced stages can pose quandaries for treatment and management. Many advanced technologies are now being applied to address these challenges. How might the detection of ctDNA be used to assess molecular residual disease and assist in cancer monitoring and management?

Drs. Billings and Aleshin: Treating advanced-stage cancer is challenging. While treatments are available, they have toxicities and can impact patients’ quality of life. Moreover, as tumors evolve over time, they may become treatment resistant. Determining treatment resistance early can have significant clinical implications.

With the advent of next-generation sequencing, it is now possible to sequence the tumor tissue and identify a set of mutations that are specific to the patient’s tumor. These mutations, which are linked to early tumor development and are not related to specific response to treatment, can be tracked later by analyzing free-floating fragments of tumor DNA—circulating tumor DNA (ctDNA)—in the patient’s blood, without the need for any additional biopsy.

Moreover, the short half-life of ctDNA provides a real-time snapshot of subtle changes in the tumor burden, and is far more effective than a radiological scan that relies on detecting a visible lesion. Such a personalized and tumor-informed approach has emerged as a sensitive, non-invasive, and cost-effective tool for identifying tumor molecules (molecular residual disease) down to a single molecule in a tube of blood.

Immunotherapy has fundamentally changed how cancer is managed. However, only a fraction of patients respond to immunotherapy, while all patients are at risk of developing side effects from this treatment. An example of how ctDNA could address this issue is a hypothetical patient who was treated with pembrolizumab (Keytruda) for her non-small cell lung cancer. Initial imaging showed a mixed result that was difficult to interpret. However, ctDNA showed a markedly elevated ctDNA level suggestive of progression. This allowed the oncologist to reconcile ambiguous findings on imaging and alter the patient’s clinical course by switching to an alternative therapy.

Our recently published study, in Nature Cancer, highlights the advantage of monitoring ctDNA dynamics in a cohort of patients with 25 different types of histologies. The study showed significantly better outcomes for patients who cleared their ctDNA posttreatment, indicating exceptional response. The study also illustrated molecular progression as early as 6 weeks in a percentage of patients who received, on average, two cycles (six weeks) of additional treatment, which could have been avoided. This shows a clear utility of ctDNA that could have enabled an earlier switch to alternative treatment with a higher degree of efficacy and a lower financial burden.

More recently, the U.S. Food and Drug Administration (FDA) approved pembrolizumab as a first-line treatment for patients with unresectable or metastatic mismatch repair deficient/microsatellite instability status (dMMR/MSI-H) colorectal cancer (CRC), which constitutes 15 percent of metastatic CRC (mCRC) patients. The remaining have a microsatellite-stable status. Both of these subtypes have shown poor expression of CEA, which is a commonly used protein biomarker. Many studies have alluded to its poor sensitivity, specificity, and unreliability in predicting treatment response or risk of relapse. We recently presented a few case examples at the Society for Immunotherapy of Cancer (SITC) conference that highlight a physician’s experience in treating patients with mCRC and the value of ctDNA over conventional methodologies.

In summary, there is strong scientific evidence showing that the incorporation of ctDNA analysis into routine clinical practice can help physicians make better-informed decisions for patients battling an aggressive disease.

Drs. Billings and Aleshin can be reached at pbillings@natera.com.

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Copyright: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Curious Dr. George | Plumbing the Core and Nibbling at the Margins of Cancer

Just Diagnosed with Advanced Lung Cancer: What Now?

Curious Dr. George
Cancer Commons Contributing Editor George Lundberg, MD, is the face and curator of this invitation-only column.

Howard (Jack) West, MD
Associate Clinical Professor in Medical Oncology and Executive Director of Employer Services at City of Hope Comprehensive Cancer Center

A new cancer diagnosis is overwhelming. Patients often ask their doctors, “What would you do if you were me?” Here, our Curious Dr. George asks lung cancer expert Howard (Jack) West, MD, how he would handle his own diagnosis of advanced lung cancer. Dr. West is a Princeton- and Harvard-educated oncologist with additional training and experience in Boston and Seattle focusing on lung cancer. He is now an Associate Clinical Professor in Medical Oncology and Executive Director of Employer Services at City of Hope Comprehensive Cancer Center in Duarte, California.

Curious Dr. George: What would you do if you personally were discovered on a routine chest X-ray to have a unilateral pleural effusion which was found by cytopathology to contain mixed squamous and adenocarcinoma cells? How would you proceed?

Dr. West: Though I’m a never-smoker, we know that is no guarantee of immunity from lung cancer, the cancer type I’ve focused on for the past two decades. Perhaps I develop a persistent cough and worsening shortness of breath over a few months. I get a chest X-ray that shows a large right pleural effusion, and a same-day chest CT confirms this and bilateral lung nodules, perhaps along with several enlarged right hilar and mediastinal lymph nodes. The effusion is drained, and the pathologist gives my doctor and me the immediate feedback that this is a carcinoma, and we quickly learn that the immunohistochemistry profile is consistent with an adenocarcinoma. Where do we go from here?

My next step is to order broad next-generation sequencing, which may entail a new biopsy, either CT-guided or an endobronchial ultrasound and biopsy of whatever is accessible. We need sufficient tissue to send off for broad molecular testing that includes a look for all of the growing collection of lung cancer “driver mutations.” These include long-established markers like a mutation in the epidermal growth factor receptor (EGFR) gene or a rearrangement in the anaplastic lymphoma kinase (ALK) gene, but now also a rearrangement in ROS1, mutation of BRAF V600E, a MET exon 14 skipping mutation, RET fusion, or fusion in the TRK gene. These genetic alterations are found in approximately 0.5% to 10% each in patients with non-small cell lung cancer (NSCLC) and far more commonly in patients with a non-squamous NSCLC tumor. They all have FDA-approved oral targeted therapies with efficacy that generally exceeds what we could expect with our best standard non-targeted approaches involving immunotherapy with or without chemotherapy. Most of these targeted therapies also better tolerated and can work for a prolonged period that may reach the range of years.

This mutation testing typically takes at least 2 to 4 weeks, but the importance of identifying one of these mutations, when present, makes it critical to seek this information at the time of initial diagnosis. Moreover, in addition to the array of markers we currently have targeted therapies for, we expect an FDA approval for an inhibitor of KRAS G12C-mutated NSCLC, seen in about 12% to 13% of advanced NSCLC, in the coming months; all in all, comprehensive molecular testing guides us to an optimal targeted therapy for at least 20% of patients, and that proportion will continue to increase as new targets with effective therapies become available.

In the hypothetical scenario of my own diagnosis, as this testing is being done we’re also testing for tumor PD-L1 expression, which identifies tumors most likely to respond well to immune checkpoint inhibitors, potentially sparing patients first line chemotherapy if they don’t receive a targeted therapy. And I’d seek to complete imaging with a PET/CT and brain MRI, in order to identify whether the cancer has spread to other sites beyond those already identified.

Once these tests are completed, I’d prioritize a targeted therapy if my tumor harbors a driver mutation. If not, I’d generally favor pembrolizumab monotherapy if my cancer is among the approximately 28% to 30% that demonstrates high tumor PD-L1 expression (greater than 50%). Otherwise, if my cancer has neither a driver mutation nor high tumor PD-L1 expression, I’d generally favor a platinum-based chemotherapy doublet with pembrolizumab—an option I would also favor in a patient with a tumor that doesn’t harbor a driver mutation and with high tumor PD-L1 if that patient had many cancer-related symptoms or otherwise showed a pattern of rapid progression in the early weeks of the workup. Though I’d be happy to sequence the immunotherapy with subsequent chemotherapy in patients in whom I’m confident they will still have the performance status to tolerate platinum doublet chemotherapy after progressing on chemotherapy, I’d favor “front-loading” with chemo-immunotherapy together in patients in whom I’m concerned I may only have “one shot on goal.”

Dr. West can be reached at JackWestMD@gmail.com or on Twitter at @JackWestMD.

Related Links:

Molecular Testing Guides Treatment for Claudius’s Lung Cancer

What’s New in Immunotherapy for Non-Small Cell Lung Cancer?

Comprehensive Molecular Testing Needed for Stage IV Lung Cancer

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Copyright: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.