Cellular density of low-grade transition zone prostate cancer: A limiting factor to correlate restricted diffusion with tumor aggressiveness

Objective To compare the mean apparent diffusion coefficient (ADCmean) and glandular density of Gleason score (GS) 3 + 3 transition zone prostate cancers (TZ-PCa) with those of the peripheral zone (PZ-PCa). Material & methods Seventy-nine men (mean age: 65 ± 6 [SD] years; range: 52–81 years) with 37 TZ-PCa (37/79; 53 %) and 42 PZ-PCa (42/79; 47 %) had prostate MRI before radical prostatectomy. Glandular cell density was semi-quantitatively evaluated in all tumors. ADCmean and glandular cell density of GS3 + 3 TZ-PCa were compared to those of PZ-PCa. ADCmean was correlated to GS in each zone. Results ADCmean of GS 3 + 3 tumors was significantly lower in the TZ (728 × 10−6±52 [SD] mm²/s; range: 670−1060mm²/s) than in the PZ (865 × 10−6 ±121 [SD] mm²/s; range: 670−1120mm²/s) (p = 0.0007), related to a significantly higher glandular density involving more than 50 % of the tumor in 58 % (7/12) of patients in GS3 + 3 TZ-PCa versus 7.6 % (1/13) in PZ-PCa (p = 0.03). ADCmean of GS3 + 3 TZ-PCa was not significantly different from that of GS 3 + 4 (p = 0.14) or GS>3 + 4 Ca (p = 0.9), whatever the zone of origin. In the PZ, ADCmean of GS 3 + 3-PCa was higher than that of Gleason>3 + 4 PZ-PCa (p = 0.02) and similar to that of GS 3 + 4 PZ-PCa (p = 0.24). Correlation between ADCmean and GS was weak for TZ-PCa (ρ = 0.32; p = 0.04) and moderate for PZ-PCa (ρ = 0.45; p = 0.003). Conclusion ADCmean of GS 3 + 3 TZ-PCa is significantly lower than that of GS 3 + 3 PZ-PCa, related to a unique dense histological pattern and reaches that of higher-grade PCa, whatever the zone of origin.