The pace of advancements in lung cancer diagnosis and treatment is encouraging for patients and the doctors who treat them. One such recent advancement is providing a new way for oncologists to learn more about individual tumors. Liquid biopsies — while still largely experimental and of limited clinical use today — may someday become an important part of cancer care.
[See: What Not to Say to Someone With Lung Cancer.]
What Is a Biopsy?
When you have an abnormality that might indicate cancer — such as a suspicious area on a CT scan of your lungs — your doctor needs to determine if it is in fact cancer and, if so, what stage it is. This information drives treatment decisions and prognosis. Usually, your doctor confirms a cancer diagnosis by extracting a small piece of tissue (a biopsy) from the abnormal area and having a pathologist examine the cells under a microscope.
Tissue biopsies are highly accurate for diagnosing and staging cancer. Pathologists also test lung cancer biopsies to see if they have any genetic mutations that might make you a good candidate for targeted therapies.
Never-smokers with lung cancer have a higher prevalence of several specific cancer driver mutations, says Dr. Leena Gandhi, director of thoracic medical oncology at the Perlmutter Cancer Center at NYU Langone Medical Center. The most common is epidermal growth factor receptor, or EGFR. “If we know a patient [with advanced disease] has this specific mutation, it can be [treated with EGFR targeted therapies].”
Sometimes, it’s difficult to get a big enough piece of tissue to both confirm a lung cancer diagnosis and look for these genetic mutations, say Dr. Geoffrey Oxnard, a medical oncologist at the Dana-Farber Cancer Institute and assistant professor of medicine at Harvard Medical School. Furthermore, some lung cancer patients are not good candidates for traditional tissue biopsies because of where their tumor is located or the risk of complications. This is one area where liquid biopsies currently play a role.
[See: 7 Things You Didn’t Know About Lung Cancer.]
Liquid Biopsies
A liquid biopsy looks for free-floating tumor DNA in a sample of blood, Oxnard says. Some tumors shed DNA into the blood stream. This is called circulating DNA. If a patient has one of these mutations, such as EGFR (as indicated by the tumor DNA), he or she may be a candidate for targeted therapy.
Currently, oncologists’ use of liquid biopsies is limited. Ghandi says there’s no way to distinguish cancer DNA in the blood from normal DNA unless you already know of a specific mutation (such as EGFR). In other words, it doesn’t help you identify new genetic abnormalities. For lung cancers in younger patients who’ve never smoked, liquid biopsies may be used in place of tissue biopsies. However, the test is only about 70 percent sensitive because not all tumor cells shed DNA, and sometimes there’s not enough measurable tumor DNA in the blood even if the tumor does shed. “It depends on the cancer’s unique characteristics,” Ghandi says. “Some [tumors] shed a lot, some not as much. If we detect an EGFR mutation through a liquid biopsy, we may not need a tissue biopsy.”
If your doctor doesn’t see tumor DNA in the blood, the cancer may just not be shedding it, Oxnard says. “We have to take a negative result with a grain of salt. If the test is negative, we have to fall back on a tissue sample.”
Of course, only 10 to 15 percent of non-small cell lung cancers have the EGFR mutation (and the other identified mutations occur in a very small percent of patients), so that limits the current usefulness of a liquid biopsy to a small portion of lung cancer patients.
There is a second use for liquid biopsies: They help identify mutations that develop during treatment but were not detected in the original biopsy. “We most often use liquid biopsies when patients develop resistance [new mutations] to targeted therapies,” Ghandi says. “Targeted therapies are not curative. They control the cancer for a time, but patients develop resistance [to treatments] in common and specific ways.” Once a patient develops resistance to a specific targeted therapy, it’s time to change to another medication (if one is available).
“Sixty percent of patients who develop resistance to EGFR do so in a very predictable way. Liquid biopsies are useful for detecting these changes,” Ghandi says.
Liquid biopsies may be a good way to monitor the effectiveness of treatment — and the development of resistance — in real time, a process called serial monitoring. Liquid biopsies may even detect mutations not found when you only take a biopsy of a single tumor lesion at a single time. For example, the genetic profile of a tissue biopsy from a different spot on the tumor, or from a metastasized tumor, may be different.
[See: 7 Innovations in Cancer Therapy.]
So far, the U.S. Food and Drug Administration has approved one liquid biopsy test that can detect EGFR mutations in non-small cell lung cancers. In clinical trials that matched results from tissue biopsy samples with liquid biopsies, the liquid biopsy results were comparable to the tissue sample most of the time (the accuracy results varied somewhat, depending on the trial).
Oncologists hope that someday liquid biopsies might help diagnose lung cancers early, when they’re easier to treat. For now, however, it’s just one more evolving tool to help better treat patients with lung (and other) cancers.
More from U.S. News
What Not to Say to Someone With Lung Cancer
7 Innovations in Cancer Therapy
7 Things You Didn’t Know About Lung Cancer
What Is a Liquid Biopsy for Lung Cancer? originally appeared on usnews.com
