Novel Diagnostic Test Uses CTCs in Blood to Guide Treatment Decisions for Patients With Prostate Cancer

SAN FRANCISCO, CA—An experimental liquid biopsy using a blood sample may determine which patients with prostate cancer will benefit from hormone therapies, according to early study findings. The findings were reported at the 2016 Genitourinary Cancers Symposium.

The test scans the entire landscape of different kinds of cancer cells in blood, which are known as circulating tumor cells (CTCs), and analyzes their genetic make-up and their morphology. The hope is that this blood test may help guide individualized decisions on the most appropriate treatments for patients with prostate cancer.

“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 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, New York, and lead author of the study.

“In addition, unlike a tissue biopsy, blood samples are easily obtained at any time so that treatment adjustments can be made sooner.”

CTCs are malignant cells shed into the bloodstream by solid tumors. These cells can be released both from the site of the original tumor and from metastases in cases of advanced cancer. Individual patients have a range of different kinds of CTCs.

Tumor heterogeneity is a likely driver of disease resistance, according to the study's findings. Therefore, single-cell characterization has potential value in identifying rare somatic subclonal alterations, since knowledge of those alterations can help researchers rationally develop therapeutic trials.

The study assessed 221 blood specimens from 179 patients with metastatic prostate cancer who were going to begin either hormonal therapy targeting the androgen receptor (enzalutamide or abiraterone) or taxane chemotherapy.

Patients whose higher heterogeneity scores indicated greater variation in CTC appearance and genetic make-up did not respond well to hormonal therapy. These patients had a shorter median progression-free survival compared with patients whose heterogeneity scores were lower (5 months vs 17 months, respectively). In addition, overall survival was 9 months among for patients with higher heterogeneity scores compared with not reached for patients with lower heterogeneity scores.

Heterogeneity scores did not appear to affect patients' response to chemotherapy.

The test still needs additional study and further clinical trials before it can be approved for use in routine clinical practice.

This study was funded by the Prostate Cancer Foundation, MSKCC SPORE, and MSKCC Core Grant.

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