Personalizing Breast Cancer: How Liquid Biopsy Testing for ctDNA, CTCs Can Promote Preventive Care

Liquid biopsy testing served as the focus of 2 abstracts presented at the San Antonio Breast Cancer Symposium in San Antonio, Texas:

• Detection of ctDNA, tumor DNA derived from plasma, and circulating tumor cells (CTCs) after neoadjuvant chemotherapy was found to be significantly associated with disease recurrence in patients with early-stage triple-negative breast cancer (TNBC)¹
• Phenotypic profiling of CTCs in patients with metastatic breast cancer showed clinically relevant heterogeneity both between and within patients²

Analyzing ctDNA to Determine Risk of Breast Cancer Recurrence

Using FoundationOne Liquid, a novel liquid biopsy test providing targeted gene and microsatellite instability-high results, researchers sought to examine whether specific biomarkers contribute to TNBC, an aggressive type of cancer that lacks common traits used to diagnose and treat most other breast cancers.

As TNBC accounts for 15% to 20% of breast cancer cases, difficulty in diagnosing and treating this subtype leaves many patients at risk. Additionally, senior study author Bryan Schenider, MD, professor of Medicine and Medical and Molecular Genetics at Indiana University School of Medicine, stresses that for these patients who have TNBC with residual disease, the risk of recurrence is exceptionally high. “Novel therapies and technologies are critical, including those that can potentially predict the risk of relapse,” said Schneider.

As the researchers note, TNBC is more likely than other types of breast cancer to spread to other parts of the body and reoccur after treatment, leaving patients in constant fear of relapse. To address this issue, researchers sought to examine the use of ctDNA, an innovative approach that could help stratify patients for future post-neoadjuvant treatment and identify patients for whom more aggressive treatment might be appropriate.

Researchers analyzed plasma samples that had been collected from 196 patients enrolled in the BRE12-158 clinical trial, a study of genomic-directed therapy versus physician’s choice of treatment after preoperative chemotherapy to patients with TNBC:

• Of study cohort, ctDNA was sequenced in 142 patients using the FoundationOne Liquid Test
• Primary endpoint measured 2-year disease free survival (DFS)

In the study analysis, mutated ctDNA was detected in 90 patients (63%), with TP53 being the most commonly mutated gene. The detection of ctDNA was additionally shown in the data to be related to an inferior DDFS at 17.2 months of follow-up, where these patients had a median DDFS of 32.5 months while patients without ctDNA had not reached the median.

After 24 months, DDFS probability was shown to be 25% worse in patients with ctDNA (56%) as opposed to those without (81%). Additionally, inferior overall survival was exhibited in patients with ctDNA as they had a mortality risk 4.1 times that of patients who are ctDNA-negative.

Brian Alexander, MD, MPH, chief medical officer of Foundation Medicine, highlighted the study findings, which suggest the potential of the FoundationOne Liquid Biopsy Test in identifying ctDNA as a potential predictor of heightened recurrence risk of breast cancer. “In the future, pending additional research, use of liquid biopsy to detect circulating tumor DNA could potentially help more accurately predict which patients may experience disease recurrence, allowing their healthcare providers to more effectively determine the recommended path of treatment,” said Alexander.

The follow-up period of the analysis is still ongoing, which may change current statistics in the data. After confirmation, Alexander suggested study results could promote further innovation within comprehensive genomic profiling (CGP). “Only 15% of advanced cancer patients are receiving CGP, and more than 60% of patients aren’t getting any genomic testing at all. We’re working to change that and encourage CGP as standard of care for all advanced cancer patients,” said Alexander.

Phenotypic Profiling of CTCs in Patients With Metastatic Breast Cancer

Building upon the previous abstract, ctDNA along with CTCs have become potential indicators of recurrence for early-stage TNBC after neoadjuvant chemotherapy. The benefit of these liquid biopsy tests may be further expanded to patients already diagnosed with metastatic breast cancer as researchers associated with Epic Sciences sought to examine the efficacy of a CTC liquid biopsy test to assist in answering frequent questions related to treatment, such as the choice between hormonal therapies and chemotherapy.

In a previous risk adjusted analysis, researchers created quantitative measures of phenotypic CTC heterogeneity in metastatic prostate cancer and found that higher heterogeneity was linked with greater survival on chemotherapy versus targeted hormonal therapies.

This led researchers to expand testing to metastatic breast cancer, which Rick Wenstrup, MD, chief medical officer of Epic Sciences, describes is not all that different. “From a biological standpoint, the prostate organ and breast actually come from the same embryological homology and there’s biological similarities. They’re both secretory organs—they’re both hormone driven and so it would be likely that, like prostate cancer, breast cancer exhibits CTCs,” said Wenstrup.

Researchers examined the feasibility of measuring CTC heterogeneity in patients with metastatic breast cancer by collecting 295 blood samples from 165 patients (84 hormone receptor (HR)-positive, 19 HER2-positive, 8 HR-positive/HER2-positive, 54 TNBC) and conducting a CTC analysis using the Epic Sciences Functional Cell Profiling platform:

• After enumeration, multi-dimensional phenotypic characterization analysis performed using protein expression and digital pathology features
• Features from CTCs among entire study cohort (n = 3994) were then compared by unsupervised clustering to asses intra-patient CTC heterogeneity among metastatic breast cancer CTC phenotypes

From the study group, CTCs were detected in 76.9% of patients with metastatic breast cancer (med=2.4 CTC/mL, Range 0 - 747), with distinct CTC subtypes characterized by morphological and protein expression features being discovered to correlate within patients. CTC subtypes that were prominent among the study group were shown as either high cytokeratin (CK) expression or lower nuclear to cytoplasmic ration with lower CK expression.

The significant heterogeneity of individual CTCs both between and within patients was noted as being further studied. “Our analysis revealed significant heterogeneity between individual CTCs both between and within patients. Identification of patients with high heterogeneity may help to identify patients unlikely to respond to targeted therapies,” said the study authors.

Wenstrup spotlighted that the time taken to address the first signs of metastasis is where these liquid biopsy tests could prove vital, as various tests over a period of time could create a lag before treatment and generate unnecessary costs. “To go back and look at what the medical costs from the first time someone comes back with recurrent symptoms to an oncologist, to when they actually start treatment, I think it would be interesting to see how much all that costs,” said Wenstrup.

Reference

1. Radovich M, Jiang G, Chitamber C, et al. Detection of circulating tumor DNA (ctDNA) after neoadjuvant chemotherapy is significantly associated with disease recurrence in early-stage triple-negative breast cancer (TNBC): Preplanned correlative results from clinical trial BRE12-158. Presented at the San Antonio Breast Cancer Symposium, San Antonio, Texas; December 10-14. Abstract: GS5-02.
2. Pramparo T, Jendrisak A, Ontiveros P, et al. Phenotypic profiling of circulating tumor cells (CTCs) in patients with metastatic breast cancer reveals clinically-relevant heterogeneity in CTC morphology and marker expression. Presented at the San Antonio Breast Cancer Symposium, San Antonio, Texas; December 10-14. Abstract: P4-01-09.