Last month, the FDA gave breakthrough status to a drug, Lynparza (olaparib, AstraZeneca), for treating some forms of metastatic prostate cancer. This means the agency will expedite review and possible approval of this new kind of therapy, a PARP inhibitor for men with advanced, refractory prostate cancer.

Until recently, men with prostate cancer that spreads after surgical or chemical “castration,” or androgen deprivation therapy, had few options. Since 2012, the FDA has approved several agents including two innovative hormone modulators, Xtandi and Zytiga. Now, based on science and drugs in the pipeline, men with metastatic prostate cancer can expect to live longer. They and their oncologists will face a growing array of treatment choices.

The idea of a liquid biopsy is to evaluate malignant bits, cells, DNA or other material in an ordinary blood sample. The concept has been floating for a long time, and is feasible now. But apart from the research setting, few of these tests have entered clinics. None are FDA approved (yet).

What’s advantageous about a liquid biopsy--if it’s accurate--is that checking for cancer in blood is a lot easier, less risky and (maybe) less costly than undergoing a biopsy of, say, a malignant spot in the liver or lung or bone. From a laboratory doctor’s perspective, though, analyzing rare malignant cells in blood, cell-free DNA and other tumor bits can be tricky.

In 2016, several types of liquid biopsy tests are in the works, with two broad types nearing clinical readiness: Examination of genetic material (cell-free DNA or circulating tumor DNA, which are not quite the same) and of circulating tumor cells (CTCs).

Circulating tumor cells refer to malignant cells that have broken off from a tumor--like breast, kidney, lung, ovarian, pancreatic, prostate and other “solid” cancers--and entered the bloodstream, where they may be very rare and hard to spot, no less to capture and analyze. If found, CTCs provide a window into a cancer's growth, as its genetic, protein and other cellular aspects change over time within an individual, and vary.

A few months ago, I met with Murali Prahalad, CEO of Epic Sciences (San Diego). We discussed the company’s methods of processing blood samples to store, identify and examine circulating tumor cells (CTCs). Since then I’ve been following reports on Epic’s method and other, competing CTC platforms.

What distinguishes Epic Sciences’ method is, chiefly, the way it captures and processes CTCs. Most other systems “pull out” CTCs from blood samples using specific antibodies, affixed to a microfluidic chip or a magnetic bead, or based on the cells’ size.

A CTC positive for the androgen receptor (image courtesy of Epic Sciences, San Diego)
