Following the Clues With Liquid Biopsies

A new role is emerging for liquid biopsies in the field of breast cancer: These tests may detect microscopic amounts of disease in the blood of a patient, even one who shows no other signs of illness, issuing an alert for therapeutic action.

These tests that can detect extremely low amounts of DNA, shed by the tumor, in the blood (circulating tumor DNA), seem poised for use in detecting recurrence in patients who have had potentially curative therapy for early-stage breast cancer. Even years after patients are deemed cancer-free, the tests can pick up minute amounts of tumor DNA in the blood that signal microscopic cancer — disease that is not yet visible on conventional scans but threatens to cause relapse. The tests could help determine not only who needs further treatment but also who does not, sparing the 20% to 30% of patients with early or locally advanced breast cancer who are essentially cured after chemotherapy from going under the knife or receiving additional therapy.

EXPANDING USEFULNESS

A new liquid biopsy assay called TARgeted DIgital Sequencing (TARDIS) has demonstrated possible utility in patients with early-stage breast cancer. This assay analyzes circulating tumor DNA to help identify the patients who have what is called a pathologic complete response, or the disappearance of tumor cells, after receiving chemotherapy prior to surgery for early-stage breast cancer. This type of response has long been associated with a higher chance of long-term cure, whereas patients who have visible tumor remaining in the breast or lymph nodes after presurgical chemotherapy are more likely to develop metastatic recurrence.

Another clinical trial investigating a different new liquid biopsy found that test capable of detecting breast cancer recurrence 11 months before patients had any symptoms or tumors that were visible via imaging. The researchers expressed hope that, in most patients, this early detection, coupled with additional therapy guided by the results, could prevent disease that spreads, which would be incurable.

Together, the findings from the two trials demonstrate the promise associated with liquid biopsies in the future of breast cancer treatment and prevention.

“Overall across oncology, liquid biopsy has application across the entire spectrum as far as diagnostic use for patients with cancer,” said Dr. Muhammed Murtaza, the TARDIS trial’s lead investigator and an assistant professor at the Translational Genomics Research Institute, an affiliate of the City of Hope in Duarte, California.

ACCUMULATING EVIDENCE

The personalized liquid biopsy that was used to detect cancer recurrence was developed by scientists at the Institute of Cancer Research and the Royal Marsden NHS Foundation Trust in London. Using the DNA found in a patient’s tumor before treatment as a reference, the test searches for miniscule amounts of that cancer-associated DNA.

The study was conducted at five U.K. medical centers from Nov. 4, 2011, through Oct. 18, 2016. Patients had breast cancer driven by hormones, overexpression of the protein HER2 or other factors and were receiving either chemotherapy followed by surgery or vice versa.

Each patient’s tumor was sequenced to identify mutations, and personalized tumor-specific digital polymerase chain reaction assays were then used to look for these mutations in blood samples taken every three months for the first year of follow-up and then about every six months. The median length of follow-up was 35.5 months. Detection of tumor DNA was associated with cancer relapse, as was the presence of tumor DNA in the blood at diagnosis, before any treatment.

“We hope that by identifying relapse much earlier, we will be able to treat it much more effectively than we can do now — perhaps even prevent some people from relapsing,” said professor Nicholas Turner, the study’s lead author.

TARDIS works in a similar way, simultaneously looking for multiple mutations in small quantities of blood. It has the ability to find trace amounts of circulating tumor DNA even in nonmetastatic cancer, in which levels are 20 to 100 times lower than in patients with advanced disease. In the study, TARDIS was used to analyze 80 blood samples taken from 33 women with nonmetastatic breast cancer at three cancer centers, two in the U.S. and one in the U.K. Their blood was tested before they got any treatment and then again after some of the patients had received presurgical therapy.

By analyzing eight to 16 known mutations in each sample, TARDIS detected 96% of circulating tumor DNA in one tube of blood in patients after treatment. The assay detected these fragments in amounts as tiny as two parts per 100,000.

The test was so sensitive it was able to find trace amounts of tumor DNA in each participant, but that didn’t mean all would relapse. Rather, the researchers found patients who had achieved pathologic complete response to preoperative chemotherapy had circulating tumor DNA levels sixfold lower than those with residual disease after presurgical therapy (0.003% versus 0.017%). Also, the patients who responded completely saw a larger drop in circulating tumor DNA during presurgical chemotherapy than their counterparts without a complete response.

“TARDIS has achieved up to 100-fold improvement beyond the current limit of circulating tumor DNA detection using clinically relevant blood volumes, demonstrating that personalized circulating tumor DNA tracking could enable individualized clinical management of patients with cancer treated with curative intent,” the researchers wrote.

PREVENTING UNNEEDED TREATMENT

This personalized approach could be used in the future to identify patients who are cured by their presurgical drug regimens and don’t need to move on to surgery or more chemotherapy, which is sometimes recommended for those who do not have a complete pathological response.

“The single most important finding is that there was a significant difference in circulating tumor DNA levels between patients who responded exceptionally well to neoadjuvant (presurgical) treatment compared with patients who still had residual disease at the time of surgery,” Murtaza said. “I think the implication of this is exciting in that ... we may be able to identify which patients are going to have residual disease at the time of surgery and who has responded completely. ... Then you could choose the extent, type of surgery and additional treatment based on this finding.”

Murtaza predicts that liquid biopsies will be an important tool in the breast cancer treatment landscape: “Liquid biopsies are likely to become more sensitive. We will likely see these blood tests being used to develop individualized treatment plans, together with imaging studies and other predictive biomarkers that are currently in use.”