PSA 4.0ng/ml以下の前立腺生検の検討 : PSA フリー/トータル比の有用性

Abstract

PSA4.0ng/ml以下の前立腺生検の経験から, PSA, PSAフリー/トータル比(PSAf/t), 直腸診(DRE)を用い, 検出率を維持しながら不必要な生検を減少させる方法を検討した。対象はPSA 4.0ng/ml以下でも癌が存在することを理解して生検を希望した症例や, 直腸診陽性の症例等232例で, 方法は一般的なPSAの感度といわれている0.80を維持しつつ, ROC曲線を用いてPSA, PSAf/t, DREを組み合わせ, PSA4.0ng/ml以下における生検の条件を導き出した。その結果, PSA4.0ng/ml以下の前立腺生検の条件をPSA 3.1ng/ml以上で, PSAf/tが27%以下, または直腸診陽性とすると, 感度0.919, 特異度0.436, 癌検出率23.2%となり, 232例でいえば3例の癌を見逃すが, 85例の不要な生検を回避できることになった。

The low specificity of the prostate specific antigen (PSA) test is considered to be a problem when PSA measurement alone is performed to detect cancer. Therefore, we examined a method to decrease the number of unnecessary biopsies while maintaining the power of the test by using PSA, PSA free/total ratio (PSAf/t), and digital rectal examination (DRE). The subjects were 232 patients with PSA levels of 4.0 ng/ml or less who underwent biopsy for prostate cancer. An endorectal ultrasound perineal biopsy was conducted, and the average biopsy core number was 21. Cancer was detected in 37 of the 232 subjects. Receiver operating characteristic curves of PSA and PSAf/t were subsequently determined. Although the area under the curve (AUC) was 0.56 for PSA alone, the AUC increased to 0.75 when the factor of positive data in DRE was taken into account. Although the AUC was 0.62 for PSAf/t alone, when the factor of positive data in DRE was added as for PSA, the AUC increased to 0.79. In addition, as a result of examining the combination of PSA, PSAf/t and DRE, the condition of the biopsy for prostate cancer in the cases with PSA of 4.0 ng/ml was determined as follows: PSA should be 3.1 ng/ml or more and PSAf/t 27% or less, or the result of DRE should be positive. Based on these criteria, the sensitivity, specificity and detection rate of cancer increased to 0.919, 0.436 and 23.2%, respectively. We consider that this approach will be useful.