Retrospective study of 238 intermediate-risk prostate cancer (IR-PCa) patients treated with definitive radiotherapy, evaluating whether pretreatment tumor ADC (from multiparametric MRI) predicted biochemical failure (BF) and distant metastasis (DM) beyond standard favorable/unfavorable risk classification, over a median follow-up of 10.3 years.
Low ADC (≤ 0.668 × 10⁻³ mm²/s) was independently associated with worse freedom from distant metastasis (HR 3.94, 95% CI 1.14–13.62; p = 0.03); combining ADC with clinical risk subgroup further stratified outcomes for both FFDM and FFBF (both p = 0.02), though only 22 BF events and 12 DM events occurred across 238 patients.
- ADC cutoff was data-derived, not pre-specified, increasing risk of overfitting. - Very few events (12 DMs, 22 BFs) limit statistical power and reliability of subgroup analyses. - The favorable intermediate-risk/low-ADC subgroup had only 7 patients, making those findings highly exploratory.
Do not yet use ADC values to change treatment selection in intermediate-risk prostate cancer — the data-derived cutoff and low event count require external validation first. However, tracking pretreatment ADC on mpMRI may be worth incorporating into prospective studies as a candidate prognostic biomarker.
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