Began AS in October 2023, after being diagnosed with low volume 3+4 and Decipher score of 0.22.

After an initial mpMRI showed PIRADS 3, 4 & 5 lesions, only one reduced T2 & DWI/ADC signal lesion (the original PIRADS 5) could be observed in my 12 month follow-up mpMRI.

So....yes...a 3+4 diagnosis (with low decipher score) can regress. I personally believe it may be due to my 90 minute/week vigorous aerobic exercise regiment, which I started upon PCa diagnosis...but who knows for sure...clinical studies & RCT's would suggest that could be the case.
https://jamanetwork.com/journals/jamaoncology/fullarticle/2783273#google_vignette
https://www.health.harvard.edu/mens-health/exercise-may-slow-prostate-cancer-growth
Recently, CoE institutions (UCSF & UCLA & John Hopkins) have all completed independent studies suggesting a healthy diet may also help slow PCa progression...but who knows for sure...

One thing I do know for sure is that my VO2 Max has increased from 40 to 47 and I have lost 25 lbs, since I was diagnosed.

- https://www.ucsf.edu/news/2024/05/427571/prostate-cancer-study-more-health-benefits-plant-based-diet

- https://www.uclahealth.org/news/release/low-omega-6-omega-3-rich-diet-and-fish-oil-may-slow-prostate

- https://www.hopkinsmedicine.org/news/newsroom/news-releases/2024/10/study-suggests-a-healthy-diet-may-help-keep-low-grade-prostate-cancer-from-progressing-to-more-dangerous-states-during-active-surveillance