I was diagnosed with prostate cancer in June this year and had a similar diagnosis to your relative i.e. category 2 (Gleason 3+4=7, with only 5% Gleason 4, the rest being Gleason 3). My PSA had increased from 3.58 in May 18, to 5.32 in March 21 and to 5.76 in April 21. This necessitated me having an MRI scan in May that found a lesion on my prostate and that resulted me in having a biopsy in June that confirmed the cancer. At that time the cancer was only found in 3 of the 13 cores that were taken, all on the right side of the prostate. Because of those findings I decided to go on Active Surveillance, subject to a further review in 3 months. Because a PSA test in September showed that my PSA had increased to 6.01, I underwent a general anaesthetic biopsy ( the earlier one in June was a local anaesthetic) and this found that 15 of the 19 core samples were cancerous - still the same grading but the cancer was throughout my prostate. It is very, very unlikely that the cancer had increased during the time between the biopsies, just that the second biopsy had found more. Because of the increase in my PSA and the volume of cancer present (though still low grade) I decided to come off Active Surveillance and opt for surgery. This took place at Addenbrookes on 21/12/21. If interested, my cancer journey can be found under my thread.
As mentioned by Chris, most men end up with prostate cancer and usually die of something else rather than of the cancer itself. It is reported that 1 in 5 men 40 and over have prostate cancer , that most men of 60 plus have it and that virtually all men over 80 have it. Another statistic is that a slow growing prostate cancer cell takes over 400 days to grow and that a 1 cm lesion could well be over 40 years old.
Finally, since being diagnosed I have found that several neighbours in my village and a number of ex-work colleagues have over the years been diagnosed with prostate cancer and all are still alive 10 years later (one is celebrating 22 years after being diagnosed at age 61). They all though did eventually opt for treatment.