by C. H. Weaver M. D., Medical Editor, updated 12/2020
Precision cancer medicine is an evolving concept in cancer care that aims to leverage new genomic information about a specific cancer to more precisely target treatment. Precision medicine seeks to define the genomic alterations that are driving the growth of a specific cancer, rather than relying on a simple broad classification of cancer solely based on its site of origin.
The rate of overall cancer mortality dropped by 29% between 1991 and 2017 in the United States, with a 2.2% drop between 2016 and 2017, according to data from Cancer Statistics 2020, American Cancer Society’s annual report on cancer rates and trends.
This progress is largely attributed to breakthroughs with checkpoint inhibitors, and other precision cancer medicines and is most notable for declines in lung cancer and melanoma mortality rates. (1)
The idea of matching a particular treatment to a particular patient is not a new one. It has long been recognized, for example, that hormonal therapy for breast cancer is most likely to be effective when the breast cancer contains receptors for estrogen and/or progesterone. Testing for these receptors is part of the standard clinical work-up of breast cancer. What is new, however, is the pace at which researchers are identifying new tumor markers, new tests, and new and more targeted drugs that individualize cancer treatment. The purpose of precision cancer medicine is not to categorize or classify cancers solely by site of origin, but to define the genomic alterations in the cancers DNA that are driving that specific cancer.
Precision cancer medicine utilizes molecular diagnostic testing, including DNA sequencing, to identify cancer-driving abnormalities in a cancer’s genome. Once a genetic abnormality is identified, a specific targeted therapy can be designed to attack a specific mutation or other cancer-related change in the DNA programming of the cancer cells. Precision cancer medicine uses targeted drugs and immunotherapies engineered to directly attack the cancer cells with specific abnormalities, leaving normal cells largely unharmed.
Not all cancer cells are alike
Cancer cells may differ from one another based on what genes have mutations. Precision cancer medicine utilizes molecular diagnostic testing, including DNA sequencing, to identify cancer-driving abnormalities in a cancer’s genome. This “genomic testing” is performed on a biopsy sample of the cancer and increasingly in the blood using a “liquid biopsy”.
Genomic tests are used to identify the specific genes in a cancer that are abnormal or are not working properly. In essence, this is like identifying the genetic signature or fingerprint of a particular cancer. Genomic testing is different from genetic testing. Genetic tests are typically used to determine whether a healthy individual has an inherited trait (gene) that predisposes them to developing cancer. Genomic tests evaluate the genes in a sample of diseased tissue from a patient who has already been diagnosed with cancer. In this way, genes that have mutated, or have developed abnormal functions, are identified in addition to those that may have been inherited.
Once a genetic abnormality is identified, a specific precision cancer medicine or targeted therapy can be designed to attack a specific mutation or other cancer-related change in the DNA programming of the cancer cells.
Precision cancer medicine uses targeted drugs and immunotherapies engineered to directly attack the cancer cells with specific abnormalities, leaving normal cells largely unharmed.
Precision cancer medicines can be used both instead of and in addition to chemotherapy to improve treatment outcomes.
Most or all cancers result from abnormal genes or gene regulation. The cause of these changes can be environmental, spontaneous, or inherited. By identifying the genomic changes and knowing which genes are altered in a patient, cancer drugs that specifically attack that gene (or the later consequences of that gene) can be used to target the cancer and avoid the more general side effects of chemotherapy.
Cancer occurs when good cells go bad. Normal cells in the body have complex control systems that allow them to replicate when the body is growing, or to replace damaged cells. When the damage to a cell cannot be fixed or when a cell reaches the end of its useful life span, the cell is programmed to die. This programmed cell death is a process called apoptosis. Cancer occurs when cells don’t follow this orderly, regulated process of growth, repair, and apoptosis.
Disruptions in orderly cell growth and repair may be caused by genetic mutations and chromosome alterations that regulate a cell’s behavior. Often there are several of these genomic abnormalities driving the cancer, but these can be different in cancers that otherwise seem to be the same. Two people with the same type of breast cancer, for example, may not respond to treatment in the same way if their cancers are caused by different combinations of mutations. Because the development and spread of every cancer is driven by a unique set of abnormalities in that individual cancer’s genetic makeup, the genetic makeup of each breast cancer may be unique and vary from patient to patient. In other words, all breast cancers are not the same, and they cannot be optimally treated using the same drug.
Answers to Frequently Asked Questions About Genomic Testing & Precision Cancer Medicine –What You Need to Know
Q: What is comprehensive genomic profiling?
A: Comprehensive genomic profiling is a testing method that can be performed on issue and blood, that uses next-generation sequencing (NGS) technology to detect the alterations known to drive cancer growth, and to identify genomic signatures and alterations to help determine if precision cancer medicines can be used to treat a specific cancer. Comprehensive genomic profiling enables the practice of precision medicine by facilitating individualized treatment decisions for the management cancer with targeted drugs and immunotherapies.
Q: How does genomic testing differ from genetic testing?
Genetic testing detects hereditary (inherited from parents) alterations in DNA while genomic testing detects acquired (over the course of a lifetime) alterations in DNA. Acquired alterations or “mutations” are responsible for the development of the majority of cancers.
Q: What role does genomic testing play in a cancer diagnosis?
A: Genomic testing can provide information about a patient’s prognosis based on the gene expression within an individual’s cancer tissue and can be used to predict if certain therapy (chemotherapy, immunotherapy, or precision cancer medicines) will be of benefit.
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Q: When should a patient with cancer get tested?
Genomic testing can occur at any time after a tissue sample (biopsy or resection) of cancer has been acquired. For some cancer types like colon cancer, patients should be tested at the time of diagnosis as there are proven precision cancer medicines that can be used. For other cancers testing at the time of recurrence may make more sense. When to test is rapidly evolving and patients should just ensure they discuss the role of genomic testing with their doctor at the time of diagnosis for optimal treatment planning.
Q: Who is eligible for the tests?
A: Any patient with a solid tumor, hematologic malignancy, or sarcoma is eligible for testing.
Q: What if tissue is not available to perform genomic testing?
A: There are two options: an additional biopsy can be performed if feasible or an individual can consider a “liquid biopsy” A liquid biopsy is performed by testing a sample of blood for the presence of circulating cancer cells, known as circulating tumor cells. Samples of blood obtained from a liquid biopsy can also be tested for cell-free tumor DNA (cfDNA), which are fragments of DNA shed by cancer cells into a patient’s bloodstream.
Q:What questions should I ask my healthcare team about genomic testing?
A: The following are the primary questions to ask your healthcare provider.
- Is genomic testing available for the type of cancer I have, to aid in determining my overall prognosis?
- Will the results of this testing have the potential to change your management of the cancer? Specifically: Will the test be able to tell me if certain therapies will be of benefit in my treatment?
- Have you had positive outcomes in using this testing with other patients?
- Is this testing covered by my insurance plan? (This type of testing can run in the thousands of dollars, though many plans cover the tests without an out-of-pocket expense.)
Q: For which specific cancer types is the role of genomic testing especially significant?
A: Genomic testing is developing at a rapid pace. Established testing is particularly advanced in colon, lung and breast cancer where several precision cancer medicines have already been developed. Genomic testing is also increasingly playing an important role in individuals with rare cancers, cancer of unknown primary and those with widely metastatic disease.
Undergoing genomic testing that looks at expression across a wide variety of genes may identify certain genes that could potentially be a target for therapy that is otherwise not considered. A change to a precision cancer medicine would have the potential to markedly improve survival.
Q: What is tissue agnostic treatment?
A: In 2020 The US Food and Drug Administration granted approval to Rozlytrek (entrectinib) for treatment of adults and pediatric patients with solid tumors that have a neurotrophic tyrosine receptor kinase (NTRK) gene fusion, Vitrakvi (larotrectinib) for the treatment of tumors that have a NTRK gene fusion, and Keytruda (pembrolizumab) for patients with unresectable or metastatic, microsatellite instability-high (MSI-H) or mismatch repair deficient (dMMR) solid tumors that have progressed following prior treatment.
These "tissue agnostic" approvals represents a major paradigm shift in how doctors and their patients will need to think about cancer treatment. Until recently we thought of breast cancer cells as having a unique biomarker target that could be treated with a precision cancer medicine. Now, in effect, the biomarker defines the cancer rather than the organ where the cancer began. These approvals were based on a biomarker frequently found across different tumor types versus the location in the body where the tumor originated.
According to the FDA Commissioner Dr. Scott Gottlieb, M.D. "These approvals mark another step in an important shift toward treating cancers based on their tumor genetics rather than their site of origin in the body.” The shift away from organ specific treatments creates some unique challenges for cancer patients and their doctors and provides hope to many individuals with hard to treat cancers who can now look to genomic testing as another way to identify their available treatment options.
Q: Do test results always lead to actionable treatment options?
A: Each individual cancer is unique and test results vary depending on the tumor type. Genomic profiling will not always identify an actionable target that can be treated with a precision cancer medicine.
Q: Do the tests apply to all types of cancer?
A: Comprehensive genomic profiling assays can help deliver meaningful molecular insights across all cancer types.
Q: What is the Impact of Precision Medicine on Clinical Trial Design?
Historically, clinical trials enrolled patients with a single type of cancer, such as lung cancer. The treatment was administered to that group of patients, and the response to therapy was measured without assessing the genomic makeup of the cancer. Now, to evaluate precision medicine, clinical trial models are being revised because evaluating precision medicine requires measuring the genetic makeup of the cancer before beginning treatment. The new model, a so-called “basket” trial, enrolls patients with similar mutations, rather than simply the same type of cancer. Patients must be evaluated and enrolled early so that genotyping studies can be performed.
Further Reading and Other Resources
- What Is a Liquid Biopsy?
- Outsmarting Lung Cancer
- Liquid Biopsy Can Help Predict Outcomes in Metastatic Triple-Negative Breast Cancer
- FDA Grants First “Tissue Agnostic” Accelerated Approval to Keytruda
- Precision Cancer Medicine Offers Hope for Treating Rare Cancers
- CancerConnect News: Advances in the management of cancer reported daily.