Recently, the term “liquid biopsy” is being used with increased frequency within the context of cancer treatment.
What, exactly, is a liquid biopsy, and how is it different from other biopsies?
The National Cancer Institute defines a biopsy as “the removal of cells or tissue for examination by a pathologist.” In order to establish a true diagnosis of cancer, all patients must first undergo a biopsy. This is essentially the only way to truly distinguish whether a tumor or atypical cells are the result of a benign condition, or cancer.
Historically, biopsy procedures used to obtain a tissue or cell sample were either an incisional biopsy, in which a sample of suspicious tissue is removed; an excisional biopsy, in which the entire area of suspicion is removed; or a needle biopsy, in which a needle is used to remove fluid or a small sample of tissue. Needle biopsies can be performed with a thin needle, referred to as a fine-needle aspiration biopsy, or a wide needle, referred to as a core biopsy.
Although these are still standard ways in which to biopsy, liquid biopsies are an area of extensive research and are proving to have the potential in becoming a critical tool in the healthcare setting for patients with cancer.
How are liquid biopsies different?
Liquid biopsies include a sample of blood that is tested for the presence of cancer cells circulating in the blood (circulating tumor cells or CTCs). Perhaps more importantly, 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 the cancer cells into the patient’s bloodstream.
Since cancer cells are constantly “shedding” parts of their DNA, specific genetic mutations (alterations) within these pieces of DNA can provide invaluable information to healthcare providers, and ultimately help to guide optimal treatment options for each patient.
Importantly, the bits of cfDNA that are obtained from a liquid biopsy can provide information to healthcare providers in the following areas:
- If, or to what extent, the cancer is responding to treatment
- Optimal treatment options specific to the DNA mutations of the cancer cells
- Earlier detection of cancer compared to other standard screening measures
- Molecular and genetic real-time changes occurring in a patient’s cancer cells in response to treatment and growth
Liquid biopsy role in guiding treatment options
Treatment for cancer is rapidly becoming more individualized and targeted towards specific molecular characteristics and/or genetic mutations of a patient’s cancer cells. Since these individualized treatment approaches completely rely upon very specific characteristics of cancer cells, identification of these characteristics from liquid biopsy samples can be an important determinant in the choice of medication most likely to be effective for each individual. Furthermore, this information can possibly eliminate treatment choices to which the cancer cells will likely not respond.
Over time, cancer cells tend to develop different genetic mutations in response to treatment and/or as they spread and grow. Therefore, multiple samples obtained from liquid biopsies throughout the treatment period can help healthcare providers understand whether the patient’s cancer cells are continuing to respond to treatment, as well as the ways in which the patient’s cancer cells are changing. This allows for ongoing tailoring of treatment regimens based upon identified changes of the cancer cells. This is in contrast to other types of biopsies which are performed prior to initiation of treatment for a “one-time snapshot” of a cancer’s characteristics. These types of biopsies do not allow for continued monitoring of changes over time inherent within cancer cells’ DNA.
Liquid biopsies have the potential to detect cancer cells within a patient’s body at an earlier stage than many standard screening methods. This may play an important role in both initial screening measures for early detection of cancer, as well as early detection of a cancer recurrence.
It often takes far fewer cancer cells to produce the DNA detectable by a liquid biopsy than the number of cancer cells needed to be detected by a scan or other laboratory methods.
Since earlier cancer detection tends to be associated with improved patient outcomes, liquid biopsies may ultimately play a critical role in the way in which screening for cancer is performed.
Ease of liquid biopsies
Biopsies that require the removal of tissue samples are often associated with pain, potential for infection, potential for scarring, medication, anxiety over the procedure, extended periods of time in the clinic, and potential soreness following the procedure. Furthermore, scans used for detection of cancer recurrences sometimes require intravenous medication, dietary changes prior to the scan, significant time for the scanning process, and significant financial resources.
A liquid biopsy can circumvent many of these issues, as all that is required from the patient is a blood sample.
The cornerstone of treatment for cancer has undergone a rapid and monumental shift towards targeting very specific molecular and genetic characteristics of cancer cells. As such, methods for identification of these targets is imperative to determine agents most effective for an individual’s cancer. For this to be achieved, rapid identification of these targets and real-time monitoring of genetic changes that invariably occur over time in cancer cells is necessary. This will ensure timely implementation of effective treatment according to identified genetic characteristics, and avoidance of treatment that is not likely to be effective, or to which the cancer cells have developed resistance. Liquid biopsies allow for real-time monitoring of the genetic changes occurring in cancer cells; a necessity which cannot be achieved in a timely manner with historic biopsy procedures.
Furthermore, the use of liquid biopsies reduces burdensome time and financial commitments associated with scans, invasive biopsies, and other laboratory procedures; can potentially identify earlier-stages of initial cancers and sites of recurrences; and does not carry the risk of the pain, scarring, anxiety, additional medication and potential for infection associated with historic biopsies.
Research is continuing into the standardizing of liquid biopsies, as well as the understanding of how the information obtained from liquid biopsy samples can truly guide continuous treatment decisions for those affected by cancer.