Liquid biopsy: A shortcut to Precision Medicine
Precision medicine has such promise. The concept of the right drug for the right patient at the right time is especially exciting because much of precision medicine relies on choosing a drug based on the patient’s own DNA. Unfortunately, obtaining the right DNA and sequencing it is not nearly as quick and easy as an episode of CSI would have you believe. If the biopsy sample is too small, the tumor is inaccessible, or the patient is too sick to be biopsied, DNA can’t be sequenced at all. Many metastatic patients have multiple lesions throughout their body, and since they are not all sampled, it is possible that actionable mutations are missed. Not all hospitals are equipped with staff or facilities to do such sophisticated analyses, so some patients don’t even know that looking for DNA mutations is an option for them. And unlike your favorite crime drama where DNA results can be delivered within an hour if the scientist is appropriately bribed or pleaded with, looking for DNA mutations in the context of a traditional biopsy takes time. Because of all the steps involved, patients may wait a month for DNA results, even in the best circumstances.
Even with all those hindrances, a lot of patients are benefitting from the DNA analysis of their biopsied tumor. Yet it is clear that we need more options. Luckily, I met some crazy smart people at a recent meeting sponsored by the FDA and AACR (American Association of Cancer Research). They know all these issues are problems, and they’ve got a good jump on how to solve at least some of them. If the main problem is that the tumor is inaccessible or the sample is too small, then we should find an accessible, renewable resource. One of our body’s most accessible and renewable resources? Blood. Many researchers have been searching the blood of cancer patients for tumor cells or DNA that could give clues about the tumor from which they came, and there is increasing evidence that in at least some cases, these “liquid biopsies” can be a valuable tool. Regardless of the tumor’s location, it is possible for cells or DNA shed by the tumor to circulate throughout a patient’s bloodstream. Even the sickest patients can usually tolerate a blood draw, and sending a blood sample to a specialty lab for analysis levels the playing field, making precision medicine available to patients treated in settings that lack sophisticated pathology laboratories. Because a blood draw doesn’t require coordinating schedules of the patient and multiple doctors or waiting for results of additional pathology tests, the turnaround time is much quicker. In the case of some metastatic patients, shortening the wait time from 28 days to 3 days can literally mean the difference between life and death.
The Promise of Liquid Biopsies
So why aren’t all doctors using liquid biopsies? Why would anyone agree to a traditional, invasive, surgical procedure? We’re not quite there yet. First, it seems that not all tumors “shed” cells or DNA, and so nothing’s going to show up in the blood of some patients. More than that, though, there still needs to be a lot of validation done showing that what you find in the liquid biopsy is the same as what you’d find with a traditional biopsy. A traditional biopsy can tell a pathologist a lot about a tumor and from that, an oncologist knows a lot about how to treat it. We wouldn’t want to take any steps back in our ability to treat cancer just because we want to make biopsies easier. Plus, we need to know that the test that is being done is reliable, repeatable, and safe. So far, only one test has been FDA approved to look for solid tumor mutations in a patient’s blood. The cobas test, manufactured by Roche, gained FDA approval to look for specific EGFR mutations in tumor DNA in the blood of patients with non-small cell lung cancer. While this represents a huge step forward for liquid biopsies, even in this case, the blood test is only being used as a screening test, as a negative (no mutation) result means that a traditional tissue sample should also be analyzed.
As a patient, I love the idea of a liquid biopsy. But as a scientist, I know that it is only useful if it is done well and fully validated. All those smart people I talked about before– they know that, too, and are working hard to get good technology to the patients. The promise of liquid biopsies for precision medicine is huge– it can get the best “right” treatment to the patient quickly, no matter where that patient is treated. Beyond that, liquid biopsies could be used to monitor a patient’s response to treatment instead of frequent scans, they could monitor the frequently unmonitored NED (no evidence of disease) population (like me!) for recurrence, and they could provide much more data in clinical trials where multiple biopsies, while preferable from a scientific standpoint, pose an unrealistic burden on patients. And so all those smart people keep working, knowing that they are providing so much hope for people like you and me.
Jamie Holloway is a both a scientist and a survivor, earning her PhD in tumor biology from Georgetown University a few years before her own breast cancer diagnosis. Now living with no evidence of disease after treatment for early stage triple negative breast cancer, she bridges the gap between scientists and researchers as a Precision Medicine Advocate for Cure Forward and as the Patient Advocate for the Metastatic Breast Cancer Project at the Broad Institute. She works with researchers as part of the Georgetown Breast Cancer Advocates and writes about her personal experience with cancer on her blog, Run Lipstick Chemo, and as a contributor to the Cure Magazine community.