New "Fluid Biopsy" Detects Cancer Without Surgery
The first step in treating cancer is characterizing an individual’s tumor, and for most cancers that means going under the surgeon’s knife and having the tumor or a piece of it removed and sent for examination by a pathologist. Because surgical biopsies are highly invasive, they are only very rarely repeated and so they only provide a single snapshot of a patient’s cancer at the moment that the tumor or piece of tissue is removed from the patient’s body for initial characterization. In addition, surgical biopsies can only be performed once a cancer has been detected by other means, which too often means the cancer is relatively far along in its development.
Enter the fluid biopsy, a method developed by researchers at The Scripps Research Institute Physical Sciences-Oncology Center (Scripps PS-OC) based on technology that captures from a patient’s blood the few circulating tumor cells (CTCs) that have broken away from even small tumors. The findings from this team of investigators show that this highly sensitive blood analysis technology provides information that may soon be comparable to that from some types of surgical biopsies. In addition, this technology provides a patient-specific means of monitoring, predicting, and understanding progression of cancer, including metastasis.
Physicist Peter Kuhn, of The Scripps Research Institute, and pathologist Kelly Bethel, of the Scripps Clinic, led the multidisciplinary team that developed the fluid biopsy or high-definition (HD)-CTC assay. Dr. Kuhn is the principal investigator of the Scripps PS-OC and Dr. Bethel is the senior scientific investigator. The team published five papers describing their work, along with an accompanying editorial, in the journal Physical Biology.
To identify CTCs, a patient’s blood sample is first cleared of red blood cells and then the remaining cells are fluorescently labeled in a way that distinguishes possible CTCs from ordinary white blood cells. It then uses a digital microscope and an image-processing algorithm to isolate the suspect cells with staining patterns, sizes, and shapes (“morphologies”) unlike those of healthy cells. Just as in a surgical biopsy, a pathologist can examine the images of the suspected CTCs to eliminate false positives and note their morphologies. Resulting CTCs that have been pathologist verified are called HD-CTCs. Dr. Kuhn emphasizes that this basic setup can be easily modified with different cell-labeling and image-processing techniques.
The five new studies not only demonstrate the accuracy and effectiveness of the new test for a number of different cancer types, but also begin to explore the utility of the technology for diagnosing and monitoring patients and improving cancer research in the lab. While other tests for CTCs typically use “enrichment” steps in which suspected CTCs are concentrated â€“ and these methods inadvertently exclude some types of CTCs â€“ the new studies show that the Scripps PS-OC fluid biopsy works well as a no-cell-left-behind process and enables a more complete analysis.
Also striking is the quality of the images. “The high definition method gives a detailed portrait of these elusive cells that are caught in the act of spreading around the body,” said Dr. Bethel. “It’s unprecedented â€“ we’ve never been able to see them routinely and in high definition like this before.”
In the first study, the research team examined 83 advanced cancer patients using HD-CTC to document the test’s sensitivity and accuracy for different cancer types. The scientists found that the test detected five or more CTCs per milliliter of blood in 80 percent of patients with metastatic prostate cancer, 70 percent of those with metastatic breast cancer, 50 percent of those with metastatic pancreatic cancer, 0 percent of healthy subjects. The current gold-standard CTC test, known as CellSearch, was notably less sensitive in detecting tumor cells in these samples.
Most patients whose CTC counts surpassed the detection threshold also showed small aggregates of CTCs, which cancer biologists term “microtumor emboli.” These are widely suspected to be incipient metastatic tumors, as well as triggers for the blood clots that often kill advanced cancer patients. In the second study, the scientists showed that HD-CTC could detect these aggregates in 43 percent of 71 patients with advanced prostate, lung, pancreas, and breast cancers, and in none of a group of 15 healthy subjects. “This tells us that HD-CTC could be helpful in studying the origins of cancer metastases and related blood clots, and for predicting them, too,” Dr. Kuhn said.
In the third study, the team used HD-CTC to compare circulating tumor cells from prostate cancer patients with cells from prostate cancer cell lines that researchers often use as convenient models for prostate cancer biology in the lab. The team found significant differences between the two classes of cells, in their cell morphology and in the way they were labeled by HD-CTC assay’s fluorescent markers. “This underscores the need for studying cancer cells from patients, not just model cancer cells that in some ways may be utterly different from the real thing,” Dr. Kuhn explained.
In the fourth study, the researchers performed HD-CTC assays on 28 patients with advanced non-small-cell lung cancer over periods of up to a year. The team was able to detect CTCs in 68 percent of samples, and found that the numbers of detected CTCs tended to go up as other measures showed cancer progression.
In the fifth and final paper of the series, the team tested the HD-CTC assay on 78 patients who had just been diagnosed with various stages of non-small-cell lung cancer. “We demonstrated that we could sensitively detect CTCs even in patients with early-stage cancer,” Dr. Kuhn said. This result points to the possibility of using the HD-CTC blood test not only to evaluate already-diagnosed cancer, but also to help detect cancer in people who are unaware they have it. “If HD-CTC works on the day after cancer diagnosis, as we’ve shown, then one can easily imagine that it would work the day before diagnosis, too,” Kuhn said. Kuhn and his colleagues now intend to study the use of HD-CTC as a potential screening test and to develop it further for use in clinical monitoring and cancer research.
The work detailed in the five papers was supported by the National Cancer Institute's Physical Sciences in Oncology initiative, a program that aims to foster the development of innovative ideas and new fields of study based on knowledge of the biological and physical laws and principles that define both normal and tumor systems. All five papers are available free of charge at the journal’s Web site.
- “Fluid biopsy in patients with metastatic prostate, pancreatic and breast cancer” View paper
- “Characterization of circulating tumor cell aggregates identified in patients with epithelial tumors” View paper
- “Cytometric comparisons between circulating tumor cells from prostate cancer patients and the prostate-tumor-derived LNCaP cell Line” View paper
- “High-definition imaging of circulating tumor cells and associated cellular events in non-small cell lung cancer patients: a longitudinal analysis” View paper
- “Fluid biopsy for circulating tumor cell identification in patients with early and late stage non-small cell lung cancer; a glimpse into lung cancer biology.” View paper
In addition, Drs. Kuhn and Bethel authored an editorial to accompany the papers. The editorial is also available at the journal’s Web site. View editorial