Serum PSA levels are currently used as screening tools for detection of prostate cancer, however, there is a relative lack of specificity. The current study found the median serum PSA level in patients with prostate cancer was significantly higher than its patients without prostate cancer (14.00 ng/ml of serum PSA in patients with prostate cancer, and 9.30 ng/ml of patients without prostate cancer), p-value < 0.001. Furthermore, the median prostate volume in patients with prostate cancer was significantly lower than its patients without prostate cancer (46.99 ml of volume in patients with prostate cancer and 62.41 ml of volume in patients without prostate cancer), p-value = 0.016. These findings were concordant with previous studies that revealed benign prostate hypertrophy could elevate serum PSA levels. [3, 4, 7]
Many studies reported PSA density (PSAD) which calculated from the PSA level (ng/ml) divided by prostate volume (ml) had more accuracy and more specificity than PSA level alone for detection of prostate cancer [5,6,7,8,9]. Most studies used TRUS determined the prostate volume, which differed from MRI in our study. The previous studies suggested PSAD cut-off ranged from 0.15 to 0.2, our study suggested the optimal cut-off at 0.16 which was also within that range.
Previous studies reported the PSA level was different among Asians and Caucasians, therefore, the PSAD and cutoff points were also different. Saema et al. reported the optimal cutoff point was 0.15 (sensitivity 78%, specificity 43%) in the Thai population with PSA levels between 4 and 10 ng/ml [15]. Sathean et al. investigated the optimal cutoff point within the Thai population with different BMI and PSA levels between 4 and 10 ng/ml. This study reported the optimal cutoff points were 0.15 in normal weight patients (BMI < 23), and overweight patients (BMI 23–24.9), and 0.06 in obese patients (BMI ≥ 25) [16]. These studies, however, used the prostate volume by measuring transrectal ultrasonography (TRUS). Previous studies reported prostate volume measuring by MRI to be more accurate than measuring by TRUS [17,18,19,20,21].
In the current study, the optimal cutoff point of PSAD for discrimination of prostate cancer was 0.16 (81.40% sensitivity, 54.70% specificity, 52.70% positive predictive value, 82.50% negative predictive value), and the area under the curve was 0.680 (95%CI: 0.609–0.751). Although the PSAD level of 0.17 demonstrated no difference in terms of sensitivity and specificity, the lower the better, especially for decreasing the unnecessary biopsy. Thai ethnic may make these results different from a few previous studies that reported the optimal cutoff points of PSAD in Brazilian, Iranian, and Indonesian patients were 0.11, 0.11, and 0.70 [8,9,10] .
In subgroup analyses of patients with serum PSA < 4 ng/ml, 4–10 ng/ml, and > 10 ng/ml, it was found that none of patients with serum PSA < 4 ng/ml was diagnosed with prostate cancer. These results could be supported that the patients with serum PSA < 4 ng/ml were low risk groups for cancer. Thus, follow-up of these patients could be more beneficial than biopsies taken. This current study also reported optimal cutoff points of PSAD in patients with serum PSA 4–10 ng/ml, and > 10 ng/ml were 0.16 (61.10% sensitivity, 76.00% specificity) and 0.30 (68.30% sensitivity, 64.30% specificity). These results were similar to those in previous studies. Lin et al. reported the optimal cutoff points in patients with serum PSA 2.5–10 ng/ml, and 10–20 ng/ml were 0.15, and 0.33 [11].
Karademir et al. reported there was a significant relationship between the PSAD and the Gleason score in prostate cancer patients [14]. The current study also found statistically significant correlations between PSAD and Gleason scores (p-value 0.014) that supported their results. These findings would help to predict the prognosis of prostate cancer patients.
We had several limitations in this study. First, this was the retrospective study. Second, we tried our best to recruit all available prostate cancer patients examined by MRI during the study period; however, there were a small number.