Pi-Rads 4 indicates a high likelihood of prostate cancer. The lesion size is big enough to warrant a biopsy for sure. I wouldn't freak out about this, talk to your doctor first and he might want to follow up with a biopsy to see if it's worth addressing (if he does, ask for a Decipher as well).

Many prostate cancers don't need treated as they are very slow growing, just because you have it doesn't mean you are in for trouble. The saying that always goes around for many men: more likely to die WITH prostate cancer than FROM it.