Seems like your medical team did some additional testing of the prostate tissue from your biopsy..

Immunohistochemical tumor markers are proteins that help doctors tell the difference between different types of cancer.

Here's a link to the three your medical team tested for in trying to determine your diagnosis given the GS 3+3 and low volume in the biopsy samples.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6753827/
Key note from this link - "In recent period, basal cell markers high molecular weight cytokeratin (HMWCK), P63 and prostate biomarker AMACR have been used as adjuvant to morphology in diagnostically challenging cases with a very high sensitivity and specificity."

Again, just my layman thoughts. It would seem another clinical data point leading to a discussion with your medical team about active surveillance vs treatment.

Kevin