I was diagnosed with stage 4 melanoma in Feb 2017. At my fourth treatment (every three weeks) of pembrolizumab, my PET and CAT scans were clear. I continued treatment for 12 months, and still get scanned every four months. Still clear 3 weeks ago. My doctor says he now gets to use the c-word with cancer patients. Minimal side effects for me. I wish for my cohorts that more reliable treatments come soon.