Macrophages in a liquid biopsy

A physician typically turns to an invasive biopsy—the removal of tissue—to determine if a tumor is benign or malignant and, if the latter, to identify the stage of the disease. In many cancer patients, cells leave the tumor, enter the bloodstream, and sometimes engender a new tumor elsewhere. Those circulating tumor cells (CTCs) are showing potential for a so-called liquid biopsy in a routine blood draw, as detailed by Chwee Teck Lim and Dave Hoon in Physics Today, February 2014, page 26 . Now Daniel Adams of Creatv MicroTech in Rockville, Maryland, and colleagues at several medical centers report using a gentle, low-pressure filtration system that caught not only CTCs but, to their surprise, some previously unknown fellow travelers they dubbed circulating cancer-associated macrophage-like cells (CAMLs). A macrophage is a shape-shifting cell found in the immune system—and in tumors—that can either repair or destroy other cells depending on the biological context. The gelatinous and fragile CAMLs, like the four shown in the figure, are gargantuan compared with white blood cells (labeled W). Thus far, the researchers have seen CAMLs in the blood of almost all cancer patients and in none of the healthy individuals they have studied. Further, they find that CAMLs interact with CTCs and respond to chemotherapy. Those findings suggest the possible usefulness of CAMLs for monitoring cancer metastasis and tracking treatment. (D. L. Adams et al., Proc. Natl. Acad. Sci. USA 111, 3514, 2014 doi:10.1073/pnas.1320198111 .)