Blocking a protein that protects tumor cells may shrink melanomas, according to results from an ongoing trial that were presented at the 10th International Congress of the Society for Melanoma Research in Philadelphia, Pennsylvania. Called PD-L1, the protein shields tumor cells from the immune system and it can be blocked by a drug called MPDL3280A. The phase I trial included 45 people with melanoma who were treated with the PD-L1 blocker, and tumors shrank in one-third of them. This PD-L1 blocker is also being tested in a phase I trial in combination with the BRAF inhibitor drug vemurafenib, as well as in several phase II trials against renal cell carcinoma and non-small-cell lung cancer (NSCLC). In addition, two drugs similar to this PD-L1 blocker (nivolumab and MK-3475) are being tested in phase III trials against melanoma.