Gina Kolata in The New York Times:
In a surprise discovery, researchers found that cells from some types of cancers escaped destruction by the immune system by hiding inside other cancer cells. The finding, they suggested in an article published this month in the journal eLife, may explain why some cancers can be resistant to treatments that should have destroyed them. The research began when Yaron Carmi, an assistant professor at Tel Aviv University, and Amit Gutwillig, then a doctoral student studying in his lab, were studying which T cells of the immune system might be the most potent in killing cancers. They started with laboratory experiments that examined treatment-resistant melanoma and breast cancers in mice, studying why an attack by T cells that were engineered to destroy those tumors did not obliterate them.
…Every time, though, he saw some giant cells that remained after the T cells had done their job. “I wasn’t sure what it was, so I thought I would take a closer look,” he said. The giant cells turned out to be cancer cells that were harboring other cancer cells, protecting them from destruction. Once the cancer cells escaped to their hiding places, T cells could not get to them, even if the immune system killed the cancer cells that were serving as cellular bunkers. “It was like seeing the devil,” Dr. Carmi said. Cancer cells, he added, can remain in hiding “for weeks or months.”
More here.