I'm not a medical professional so take my layman comment with a grain of salt. First, getting a second read on the MRI is a good idea. But if it's still a PI-RADS 4 the doctor is probably still going to want a biopsy. If the second MRI read is PI-RADS 3 you might consider a PSE test as well for an additional indication as to whether or not it's cancer. But if the PSE indicates cancer or the 2nd MRI opinion is also PI-RADS 4, then in my layman's opinion you're going to need a biopsy (tissue sample) to confirm if it's cancer and gauge it's aggressiveness. But a trans-perineal biopsy is usually well tolerated by the patient. I had one at age 70 and it wasn't a big deal at all. In fact, the next day got in my car for a 10 day road trip and was just fine. If it comes to a biopsy, I'd try to have a fusion biopsy if at all possible so you have better assurance they sampled the lesion. But as @mjp0512 said, if you have prostate cancer and it's aggressive, you really want to catch it early as you'll have a much better prognosis and more treatment options as compared to catching it later. As far as I know the only way to measure its aggressiveness is to look at the cells to determine the Gleason score and a test like the decipher, both of which require a tissue sample (hence biopsy). But as I said, I'm not a medical professional so this is just my laymans opinion. Best wishes.