In the near future, a vial of blood may be all that’s needed to track cancers and make important decisions about chemotherapy and other treatments—without the need for risky and potentially uncomfortable biopsies.
Latest development: Blood tests known as “liquid biopsies” are already used routinely for certain lung cancer patients. The genetic information of other cancers, including melanoma and malignancies of the breast and pancreas, can also be found in a vial of blood.
What you need to know about this new type of biopsy…
Traditional biopsies, known as tissue biopsies, are a standard part of cancer care. They are done to confirm or rule out a cancer diagnosis…to identify and characterize different types of cancer…and to track cancer changes over time.
With tissue biopsies, small portions of tissue are surgically removed or extracted with a needle and sent to a laboratory for analysis. The procedure comes with the risk for tissue damage, infection or other complications. It’s also highly stressful for patients who are already dealing with the challenges of having cancer.
Another drawback: Up to 20% of tumors can’t be biopsied at all. They may be located in an inaccessible part of the body or too close to a vital structure (such as an important blood vessel). Or the procedure might be too risky for a patient who’s already seriously ill.
With liquid biopsies, all the doctor needs is a blood sample. What information can be gleaned from a vial of blood? When tumor cells die, they cast off small amounts of DNA into the bloodstream. A blood test can analyze the DNA and map genetic abnormalities that may affect subsequent treatments. The tests can also detect whole tumor cells that malignancies sometimes shed. The cancer cells themselves can be analyzed for important abnormalities that may guide treatment decisions.
The genetic information provided by image-guided tissue biopsies and liquid biopsies can be used to tailor treatments for specific cancer patients. Genetic alterations that drive certain cancers can be detected before cancer treatment begins, or they can emerge during therapy or at some time in the future. Examples of genes that could be detected with either a liquid or tissue biopsy and potentially affect cancer care for certain malignancies…
• Breast cancer. About 20% of breast cancer patients have genetic factors that cause them to produce high levels of the HER2 protein. Standard chemotherapy drugs don’t work well for these patients, but they often respond to targeted therapy drugs such as trastuzumab (Herceptin).
• Melanoma. For the 40% to 60% of melanoma patients with a specific mutation of the BRAF gene, targeted therapy drugs such as vemurafenib (Zelboraf) are a good choice.
• Lung cancer. About 5% of lung cancer patients have a mutation in the ALK gene and may not respond (or may stop responding) to standard chemotherapy. However, these patients often do respond when they are given targeted drugs such as ceritinib (Zykadia).
Promising research: Scientists recently used liquid biopsies to identify genetic mutations in patients with colorectal, biliary (related to the bile duct) and other gastrointestinal cancers. They found that nearly 80% of patients who had become resistant to drug therapy had a specific genetic alteration…and about half had multiple genetic mutations. With this information, oncologists will know what treatments to start—or when it’s time to switch treatment strategies.
Liquid biopsies are still so new that there’s no definitive research on their reliability.
The largest study done so far: Research presented at the 2016 annual meeting of the American Society of Clinical Oncology looked at 15,000 blood samples taken from patients with a variety of cancers. For several hundred of the patients, tissue biopsies were also available. In a head-to-head comparison, the same genetic mutations that appeared in tissue biopsies were also found to be present in the liquid biopsies between 94% and 100% of the time.
More good news: In the same study, the genetic changes were detected in nearly two-thirds of patients and provided critical information for oncologists—when to choose certain drugs, for example, or when to encourage patients to enroll in a genetic abnormality-directed clinical trial.
It is too soon to conclude that liquid biopsies will become the new gold standard for identifying and tracking cancer-related gene abnormalities.
The current tests have inherent limitations. Some cancers, particularly those that are small and early stage, don’t shed detectable levels of DNA into the blood. A blood test would miss these cancers, but an image-guided tissue biopsy may not.
Expense is another factor. A liquid biopsy can cost more than $5,000. It’s covered by some, but not all, insurers. While the test isn’t cheap, it might be a bargain compared with some traditional biopsies. A lung cancer tissue biopsy usually costs about $14,000 and has a known rate of complications, including pneumothorax (air in the chest cavity), bleeding and infection. A blood “stick” is much easier—and safer.
The Guardant360, one of the most widely used “liquid biopsies,” looks at 73 different genes that could be tied to melanoma as well as lung, breast, colorectal and pancreatic cancers. Since the testing can be done with a routine blood sample, there are no additional risks—and you will be spared the discomfort of a traditional biopsy.
