Examining responses that were not guideline concordant, we found that the errors made by the RAG-LLM arose from (1) the rule-based nature of the CCI calculator, which precluded a patient aged 72 years from PSA screening despite strong risk factors for prostate cancer and (2) erroneous interpretation of a normal PSA result as “moderately elevated,” triggering a reactive repeat PSA test, which in actuality was unnecessary. This evidence concerns the gene KLK3 and prostate cancer.