ALEXANDRIA, Va. – An early study suggests that an experimental new blood test may help guide individualized decisions on the most appropriate treatments for patients with prostate cancer. The new non-invasive “liquid biopsy” scans the entire landscape of different kinds of cancer cells in blood and analyzes their appearance (e.g., shape and size) and genetic make-up to predict which patients will benefit from hormone therapies. The study will be presented at the upcoming 2016 Genitourinary Cancers Symposium in San Francisco.
“Not all men respond equally to either enzalutamide or abiraterone, and some men don’t respond at all. If the test is validated, it could be used to help select the treatment to which a patient is more likely to respond, sparing the toxicities that may result from one that is ineffective,” said lead study author Howard I. Scher, MD, a medical oncologist and chief of the Genitourinary Oncology Service at the Memorial Sloan-Kettering Cancer Center (MSKCC) in New York. “In addition, unlike a tissue biopsy, blood samples are easily obtained at any time so that treatment adjustments can be made sooner.”
Solid tumors shed malignant cells into the bloodstream, which are called circulating tumor cells (CTCs). In patients with advanced cancer, CTCs are released both from the site of the original tumor, as well as from areas where the cancer has spread (metastases). Prior research has shown that individual patients have a range of different kinds of CTCs.
The experimental test involves placing a blood specimen onto a glass slide and staining it with special dyes to distinguish normal blood cells from CTCs. A machine then scans the slide and analyzes the various features of the CTCs, such as size and shape. “This works very much like facial recognition software used at airport security. The software can quickly identify a cell by looking at its different features,” explained Dr. Scher. Researchers can then select individual cells of interest, pick them up from the slide and perform an analysis of genetic abnormalities.
A total of 221 blood specimens from 179 patients with metastatic prostate cancer were assessed in this early study. The patients were about to begin either hormonal therapies targeting the androgen receptor (enzalutamide or abiraterone) or taxane chemotherapy.
The researchers found that patients with more variation in CTC appearance and genetic make-up (i.e., higher “heterogeneity score”) did not respond well to hormone therapy. Compared to patients with a low heterogeneity score, patients with a high heterogeneity score experienced shorter median progression-free survival (5 months vs. 17 months) and overall survival (9 months vs. not reached). In contrast, heterogeneity scores did not appear to affect patients’ response to chemotherapy.
Before the test can be approved for use in routine practice, it needs to be thoroughly validated. Researchers will also need to determine in a clinical trial how well the test results predict patient outcomes.
This study received funding from the Prostate Cancer Foundation, MSKCC SPORE, and MSKCC Core Grant.