Detection of clinically insignificant prostate cancer by allelic imbalance analysis

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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 mm^3 ; others, <500 mm^3. 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 mm^3 or > 500 mm^3 ; TV < 200 mm^3 or > 200 mm^3 ; and TV < 200 mm^3 or 200 mm^3 〓 TV < 500 mm^3 or〓500 mm^3 ; 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%). No significant differences in LOH frequencies were found at any of these TV settings. When insignificant tumor is defined as TV < 200 mm^3 or < 500 mm^3, 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.