Clinicopathological characteristics
Demographic and clinicopathological features of all the EOC patients, including the training group (n=88) and validated group (n=30), were listed in Table 1 and Table 2. Patients with FIGO stage I, II, III and IV accounted for 14(11.86%), 29(24.58%), 38(32.20%), and 37(31.36%), respectively. Patients diagnosed as low pathological grade (G1-G2) and high pathological grade (G3) accounted for 26 (13.56%) and 92 (86.44%) of all patients involved. There were 44 (37.29%) patients with histology-proved lymph node metastasis, and 36 (30.51%) presented with ascites. The mean value (± SD) of CTC counts, M-CTC percentage and CA-125 was 8.70 ± 5.69, 0.24 ± 0.35, and 890.71 ± 365.41 (U/mL), respectively. The median time of follow-up was 30 months (range, 24-35 months). The investigated clinical data of patients from both groups were analyzed and no significant difference were found, indicating no selection bias ( p-value >= 0.05).
Univariable and multivariate regression analysis of training group
Figure 3 showed that patients suffered cancer recurrence had higher CTC counts and M-CTC percentage (p-value < 0.05). To further determine the independent predictive indexes, univariate and multivariate analyses were performed (Table 3). In the univariable COX regression analysis, parameters including age, tumor size, menopausal status, pathological grade, FIGO stage, lymph node metastasis, ascites, CTC counts, M-CTC percentage, albumin level, CA-125 and HE4 were significantly associated with ovarian cancer recurrence. Then, these indicators were included into the multivariate Cox hazards model for further analysis. The results demonstrated that pathological grade (HR, 1.382; 95% CI, 1.104-3.965; p = 0.041), FIGO stage (HR, 2.391; 95% CI, 1.230-4.377; p = 0.011), lymph node metastasis (HR, 1.312; 95% CI, 1.029-2.975; p = 0.039), ascites (HR, 1.215; 95% CI, 1.067-1.806; p = 0.026), CTC counts (HR, 1.187; 95% CI, 1.098-1.752; p = 0.012), M-CTC percentage (HR, 1.098; 95% CI, 1.047-1.320; p = 0.009) and CA-125 (HR, 1.097; 95% CI, 1.021-1.373; p = 0.028) were independent prognostic factors for OS of EOC patients (Table 3).
Construction of EOC recurrence nomogram
The clinicopathological parameters (FIGO stage, pathological grade, lymph node metastasis, ascites, CTC counts, M-CTC percentage and CA-125) were selected by both univariable and multivariate Cox logistic regression were channeled into construction of the nomogram (Figure. 4A), while a nomogram without CTC counts and M-CTC percentage were also constructed for comparation (Figure. 4B). In the training group, the C-index of 1000 sample bootstrap was 0.913 and 0.832 for the nomogram with and without CTCs. When applied to the validation cohort, the C- index was 0.874 and 0.782, respectively, which showed significant prognosis value of discrimination in both cohorts for the nomogram with CTC counts and M-CTC percentage.
Further risk stratification in EOC patients calibration curves manifested that the probability of predicted 1-year and 2-year recurrence rate in nomogram were well consistent between the predicted outcome of cancer recurrence and actual observation in the training group (Figure. 5A and 5B). Moreover, in the external validation group, the calibration curves also illustrated good validation between predicted and observed 1- and 2-year recurrence proportions (Figure. 5C and 5D). The discrimination and calibration validation of external group definitely certificated that nomogram models in this study is comparatively accurate enough to predict the recurrence probability of patients with EOC.
Risk stratification in EOC patients
According to the ROC curve, the AUC values of CTC counts, M-CTC percentage and CA-125 were 0.8073, 0.8262 and 0.7735, respectively (Figure. 6A). For the nomogram with/without CTC counts and M-CTC percentage, the AUC were 0.8705 and 0.8097 (Figure. 6B). Meanwhile, as illustrated in Figure. 6C and 6D, the discriminatory value of CTC counts and M-CTC percentage was significant among ovarian cancer patients, with the log-rank P value of 0.0241 and 0.0107, respectively. When stratified by CTC counts, patients with CTCs >= 9 and 5<=CTCs<9 were associated with a 1.98-fold increase (95% CI, 1.04-2.47) and 1.24-fold increase (95% CI, 1.07-2.29) of recurrence rate, comparing to those with CTCs < 5, while patients with M-CTC percentage >= 0.3 and 0.1 <= M-CTC < 0.3 were associated with a 2.10-fold increase (95% CI, 1.54-2.66) and 1.43-fold increase (95% CI, 1.14-2.53) of recurrence rate, comparing to those with M-CTC < 0.1.
Moreover, the patients were then divided into three risk groups (low-, intermediate- and high-risk groups) based on the nomogram-predicted recurrence probabilities. For the nomogram without CTCs, when compared with the low-risk group, the high-risk and intermediate-risk groups were associated with a 2.37-fold increase (95% CI, 1.28-4.83) and 1.48-fold increase (95% CI, 1.17-2.64) in the risk of recurrence, with the p value of 0.0010 (Figure. 6E). Meanwhile, in the CTCs based nomogram, the high-risk and intermediate-risk groups were associated with a 3.14-fold increase (95% CI, 1.16-4.50) and 1.86-fold increase (95% CI, 1.70-3.96) in the risk of recurrence, with the p value of 0.0002 (Figure. 6F).