Dabrafenib + Trametinib + PDR001 In Colorectal Cancer

* This research study is a Phase II clinical trial. Phase II clinical trials test the safety and effectiveness of an investigational drug combination to learn whether the drug combination works in treating a specific disease. "Investigational" means that the drug combination is being studied. * The FDA (the U.S. Food and Drug Administration) has not approved PDR001 as a treatment for any disease. * The FDA has not approved dabrafenib and trametinib for your specific disease but it has been approved for other uses, whether alone as single agents, or given together as in this study. * This research study is studying a combination of drugs as a possible treatment for metastatic colorectal cancer characterized by BRAF V600E mutation. * All humans have a gene called BRAF which is responsible for sending signals to proteins called B-Raf inside of cells that help them grow. In some metastatic colorectal patients, this gene mutates and causes cancer cells to grow in uncontrolled ways. \--- Dabrafenib is a drug that is thought to inhibit the mutant BRAF activity, which may serve to slow or stop cell growth of metastatic colon cancer. * Mitogen-activated protein kinase (MAPK) is a pathway that helps to activate the BRAF mutated genes. The MAPK pathway is commonly found to be overactivated in BRAF mutated tumor cells. MEK (which refers to MAPK/ERK Kinase) enzymes are essential to the activity of the MAPK pathway. * Trametinib inhibits the MEK enzymes in order to shut down the MAPK pathway, thus blocking the pathway that helps the cancer cells grow uncontrollably. * PDR001 is a drug which binds to PD1 on immune cells and is believed to block binding of PD-L1 and PD-L2. PD-L1/PDL1 and PD-L2/PDL2 are often used by cancer cells and to escape the power of the body's immune system so that they cannot be fought. By blocking that binding of the molecules, the body's immune system may reach and fight the cancer cells. Researchers are hoping that administration of all three of these drugs may help anti-cancer activities work together to slow or stop the cancer growth and may help your own immune system damage or destroy the existing cancer cells.