Oncology clinicians are testing a new tool to help determine patients’ response to treatment, evaluate prognosis and make better-informed decisions — The CellSearch Circulating Tumor Cell Test.
“The value of counting circulating tumor cells is emerging, and its benefit is that it, hopefully, will be a biomarker for metastatic prostate cancer,” said Anthony DeLaCruz, NP, MSN, OCN, a research nurse on the CTC numeration trial team at Memorial Sloan-Kettering Cancer Center in New York City. “The data to date that’s been presented indicates changes in CTC count can predict overall survival and the patient’s response to a particular treatment.”
CellSearch CTC from Veridex, a Johnson & Johnson Co., is a blood test that captures and counts circulating tumor cells, which are cells that have detached from the tumor and are traveling in the bloodstream. It is the only CTC test cleared by the U.S. Food and Drug Administration for use with breast, prostate and colorectal cancers.
Fran Fanning, RN, OCN, a nurse at Florida Cancer Specialists in Clearwater, which orders the test for patients with biopsy-proven breast, prostate or colon cancer, said she believes counting circulating tumor cells can improve patient care.
“You now have a greater picture,” said Fanning, explaining that while traditional biomarkers for tumor activity or hormonal levels can indicate the cancer is back, the CTC test can show efficacy of the chemotherapy.
“It has great promise in terms of technology as a cancer monitoring test,” said Michele Myers, RN, BSN, OCN, an access nurse at the Center for Thoracic Cancers at Massachusetts General Hospital in Boston, which is using CellSearch in clinical trials to develop and commercialize the next-generation CTC test. Trial physicians are not using results from CTC testing to make treatment decisions, she said.
RN roleMichele Myers, RN
Nurses explain the test to patients and how providers will use the results for their treatment during testing.
“As the role of oncology nurses and nurse practitioners evolve, one of our central roles is educating the patient,” DeLaCruz said. “When these new diagnostic tests become available, it’s imperative nurses have the knowledge to discuss these tests with colleagues and their patients. It’s important to understand the technology.”
The CellSearch assay detects certain cell markers expressed by tumors of epithelial cell origin, called adenocarcinomas. A peripheral blood sample drawn from the patient is treated in the laboratory with a CellSearch kit. Tiny, protein-coated magnetic balls mark the cancer cells, which are then stained with fluorescent markers. A magnetic field is applied, forcing magnetically marked cells to move to the surface where they are analyzed, counted and verified by a pathologist.
The test is capable of detecting one circulating tumor cell among approximately 40 billion blood cells, said Robert McCormack, PhD, head of technology, innovation and strategy at Veridex.
The greater number of cells present, the worse the prognosis. In metastatic breast or prostate cancer, fewer than five circulating cancer cells predicts better survival than a count of five or more. In colorectal cancer, three is the cutoff point.
“As nurses, we explain what the counts mean, definitive to their cancer and relating it all together,” Fanning said.
Using the results
Physicians may use the CellSearch CTC test as an independent predictor of survival. The test also may be used as an adjunct to other tests and imaging studies. CTC counts can predict treatment response earlier than imaging studies or prostate-specific antigen levels. Providers may begin checking for CTC at diagnosis and retest as early as following the first round of chemotherapy to monitor changes in prognosis.
“In the beginning, we were utilizing it for patients who were on chemotherapy for a while, through a second or possibly a third regimen, to see the effectiveness of the [therapy],” Fanning said. “Now we are using it on just about everybody from the beginning, patients who have never been treated, to see where the circulating tumor cells are.”
When oncologists at Florida Cancer Specialists start noting higher levels of circulating tumor cells, they may re-evaluate the therapeutic regimen and try a different approach. On the other hand, if the circulating tumor cell counts are declining, it indicates the therapy is effective.
“It’s another test to reconfirm [to the patient] that their treatment is working or why the doctor is switching [to a different therapy],” Fanning said.
While some providers use CTC to monitor breast, prostate and colorectal cancer patients’ progress and as a prognostic indicator, clinical research sites are investigating using the test in patients with other solid tumors, such as those in the lung, and as a diagnostic tool for personalizing patient care.
“I see this as a test that probably all cancer [patients] will benefit from,” Fanning said. “This is going to be one of these for all cancer types across the board.”
McCormack explains that the next generation of CellSearch aims to further automate the characterization of tumor cells in hopes the information will allow physicians to deliver more targeted therapies and monitor how patients are responding. The platform being developed at Massachusetts General will isolate and explore the biology of rare cells at the protein, RNA and DNA levels.
Thomas P. Baker, MD, a physician at Walter Reed Army Medical Center in Washington, D.C., and colleagues are attempting to validate use of the circulating tumor cell technology as a breast cancer screening tool.
“It can potentially be used for detection, but they are in the beginning stages of developing this,” Myers said. “The hope is for it to become a cancer screening tool.”