Prediction of clinically insignificant prostate cancer by detection of allelic imbalance at 6q, 8p and 13q

The criterion tumor volume (TV) for clinically insignificant prostate cancer has been reported, but it differs from study to study: some have reported TV < 200 mm³; others, < 500 mm³. The aim of the present study was to distinguish clinically insignificant cancers from significant ones using molecular biological methods. A total of 184 microscopic cancers (MC) defined as limited within a 3 mm circle and 82 main tumor (MT) nodules were selected. Thirteen microsatellite loci at 6q22, 8p23.2–23, 13q14 and 13q33 were evaluated for loss of heterozygosity (LOH). MT were subgrouped as TV ≥ 500 mm³ or <500 mm³; TV ≥ 200 mm³ or < 200 mm³; and TV < 200 mm³, 200 mm³ ≤ TV < 500 mm³ or TV ≥ 500 mm³; and frequencies of LOH were compared between these three groups. Frequencies of LOH at 6q16–21, 6q22, 8p23.1, 8p23.2, 13q14 were significantly lower in MC (1.0%, 2.7%, 1.9%, 1.1% and 5.4%) than in MT (30.9%, 40.4%, 12%, 8.7% and 20.6%), but no significant differences in LOH frequency were found within each of the three TV groups, between each cut-off. When insignificant tumor is defined as TV < 200 mm³ or < 500 mm³, it should include tumors with malignant potential equivalent to larger tumors. It is suggested that in order to identify insignificant tumor within a strict safety range, TV should be set lower.