3.1 Basic characteristics of the enrolled patients
In this study, a total of 24 and 126 specimens were included in the lPCa and cPCa group separately. The median (IQR) age for lPCa group was 74 (53-80) years old; and the median (IQR) age for cPCa group was 71 (52-80) years old. There was no significant difference in median age between the two groups. Patient characteristics are displayed in Table 1.
According to Table 1, compared with lPCa, the tumor malignancy was significantly higher in cPCa group, cPCa had a significantly higher probability of having ISUP grade ≥ 2, tumor volume ≥ 0.5ml or EPE, with the odds ratio (OR) = 10.39 (95% confidence interval [CI]: 3.64-29.69), 32.68 (95%CI: 8.95-119.36) and 6.54 (95%CI: 2.11-20.33) respectively. The quantity of clinically significant tumors in cPCa group was significantly higher than that in lPCa group (P<0.001)
3.2 Tumor malignancy of latent prostate cancer and clinical prostate cancer
The basic characteristics of lPCa are shown in Table 2A. In lPCa group, there were a total of 45 tumor lesions from 24 lPCa cases. The median prostate volume and tumor volume were 29.4ml and 0.009ml respectively, with median ITV = 0.032ml. As for the csPCa analysis based on index tumor lesion, 3 cases were ≥ 0.5ml, accounting for 12.5% of the total. 54.2% of the lPCa cases had ISUP grade ≥ 2, and 11 (45.8%), 8 (33.3%), 0 (0%), 1 (4.2%) and 4 (16.7%) were ISUP grades 1-5 respectively. Concurrently, in total 45 tumor lesions, 21 of them were ISUP grade ≥ 2, and among which 9.5% were ≥ 0.5ml, 23.8% had EPE. Among 16 ISUP grade ≥ 2 tumor lesions meeting the condition of tumor volume < 0.5 ml and confined to the prostate, 12 of them (75.0%) were ISUP grade 2.
The basic characteristics of cPCa are shown in Table 2B. In cPCa group, there were a total of 429 tumor lesions in 126 cases with the median prostate volume = 34.5ml. The median tumor volume was 0.044ml (0.006-0.461ml), with the median ITV = 1.545ml. As for the csPCa analysis according to index tumor lesion, the tumor volume of 104 cases were ≥ 0.5ml, accounting for 82.5% of the total. The ISUP grade of 92.1% cases were ≥ 2, and 10 (7.9%), 59 (46.8%), 33 (26.2%), 10 (7.9%) and 14 (11.1%) were ISUP grade 1-5 respectively. In total 429 tumor lesions, 359 of them were ISUP grade ≥ 2, among which 28.1% were ≥ 0.5 ml, 22.6% had EPE. Among 242 ISUP grade ≥ 2 tumor lesions meeting the condition of tumor volume < 0.5 ml and confined to the prostate, 205 of them (84.7%) were ISUP grade 2.
3.3 Tumor spatial distribution of latent prostate cancer and clinical prostate cancer
As shown in Table 3, the intra-group analysis demonstrated that the index tumors were more likely to occur in PZ than TZ, the quantity of tumors involving the apical 1/3 and middle 1/3 were significantly higher than that of the basal 1/3 for both lPCa and cPCa groups. (P=0.040) Whereas there was no statistical difference in the distribution of lesions between the anterior and posterior zones.
As for the total tumor aspect, intra-group analysis verified that tumor lesions were more prone to occur in PZ than TZ, and no significant difference was detected in tumor distribution between the anterior and posterior zones for both two groups. As for the vertical direction, in lPCa group, the tumors involving basal 1/3 were significantly less than those involving apical 1/3 and middle 1/3. Moreover, in cPCa group, tumor lesions were more likely to occur at the apical 1/3 when compared with the middle 1/3 (P=0.025), while that difference was not detected in lPCa group. (P=0.396).
In addition, we further compared the spatial distribution of tumor lesions between lPCa and cPCa. Our results in Table 3 indicated that for both index and total tumor lesion, there was no significant difference in spatial distribution between the two groups in horizontal direction (anterior and posterior), vertical direction (apical 1/3 middle 1/3 and basal 1/3) and morphology aspect (peripheral and transitional zone). The spatial distribution of the two groups has the same characteristics: the majority of lesions are located at PZ, with roughly equal distribution in the anterior and posterior zones. Lesions located at the apical 1/3 and middle 1/3 are more common than those located at the basal 1/3.