Characteristics of patients
A total of 580 consecutive CRLM patients at two Chinese medical centers were enrolled. 434 patients were from cohort 1, and 146 patients were from cohort 2. Clinicopathology and treatment characteristics were listed in Table 1. All enrolled patients were Chinese individuals, the average age at diagnosis was 59. The median follow-up time was 60.5 months, whereas median OS was 59.5 months (95% CI, 58.4-70.6) in the pooled cohort, 58.9 months (95% CI, 46.2-71.6) in cohort 1 and 63.3 months (95% CI, 61.3-67.8) in cohort 2, respectively (Supplementary Table 1).
Overall, clinical features were well balanced between the two cohorts, except that patients in cohort 1 had a higher proportion of synchronous CRLM (95.2% vs. 69.4%), T4 stage of primary tumor (83.2% vs. 64%), well to moderately differentiated pathology (87.7% vs. 76.3%), and LDH levels above ULN (23.3% vs. 13.6%) than patients in cohort 2 (Supplementary table 1).
LDH levels and correlations with clinical characteristics
The relationship between serum LDH and clinicopathological parameters was detailed in Table 2. In summary, serum LDH levels showed no statistical difference when stratified by demography characteristics (age, gender), primary tumor characteristics (tumor location, pathology differentiation, T and N stage, KRAS and BRAF mutation), and metastatic site characteristics (presence of extrahepatic disease, number of CRLM, perioperative chemotherapy).
However, we observed patients with a maximum diameter of CRLM ≤ 2.5cm (the median diameter) had a higher proportion of elevated LDH levels than patients with a maximum diameter of CRLM > median (24.2% vs. 9.7%, P < .001). Patients with elevated CEA also had a greater possibility of having elevated LDH than those with normal CEA levels (18.9% vs. 10.7%, P = 0.011). A similar trend was observed for CA19-9 levels (P = 0.006). Patients with synchronous CRLM had a higher proportion of elevated LDH than those with metachronous CRLM (17.9% vs. 10.1%, P = 0.033). In addition, patients with CRS of 4-5 had higher proportion of elevated LDH than patients with CRS 2-3 or CRS 0-1 (51.2% vs. 14.2% vs. 8.7%; P < .001).
Cox regression analysis of relapse-free survival and overall survival
Due to some missing data for the baseline variables (details in Table 1), 490 patients were finally included in the multivariable model. Elevated preoperative LDH levels (defined as LDH > ULN) was found to be the strongest prognostic factor for OS (Table 3).
In the univariate analysis, age, pathology differentiation, T stage of the primary tumor, lymph node metastases of the primary tumor, preoperative CEA and CA19-9 level, number of CRLM, maximum diameter of CRLM, presence of extrahepatic metastases, preoperative chemotherapy, R0 resection margin, and LDH levels were significant predictors for OS.
After adjusted for the above clinicopathologic parameters, eight factors were ultimately identified as independent prognostic makers for OS in the multivariate analysis: age (HR, 1.03; 95% CI, 1.01-1.04; P < .001), lymph node metastasis of the primary tumor (HR, 1.70; 95% CI, 1.27-2.27; P < .001), preoperative CA19-9 (HR, 1.47; 95% CI, 1.09-1.98; P = 0.012), the number of CRLM (HR, 1.13; 95% CI, 1.07-1.20; P < .001), the maximum diameter of CRLM (HR, 1.07; 95% CI, 1.01-1.13; P < .001), extrahepatic disease (HR, 1.61; 95% CI, 1.03-2.54; P = 0.039), R0 resection margin (HR, 0.56; 95% CI, 0.37-0.84; P = 0.006), and elevated preoperative LDH levels (HR, 1.73; 95% CI, 1.22-2.44; P < .00781).
In the stratified analyses for each cohort, LDH remained its independent prognostic value for OS in the multivariate analysis, both in cohort 1 (HR, 1.77; 95% CI, 1.17-2.69; P < .001; Supplementary Table 2) and cohort 2 (HR, 3.71; 95% CI, 1.75-7.89; P = 0.001; Supplementary Table 3)
In terms of RFS, LDH remained an independent predictor in the multivariate analysis (HR, 1.53; 95% CI, 1.01-2.03; P = 0.042), along with lymph node metastases of primary tumor, number of CRLM, and maximum diameter of CRLM (supplementary Table 4).
Additionally, in the sensitivity analysis in cases with available data of KRAS mutation status, only number and size of CRLM were independent predictors for OS in multivariable models, probably due to the limitation of sample size (Supplementary Table 5).
Survival outcomes according to LDH levels and subgroups analysis
In the pooled cohort, patients with elevated LDH showed impaired OS compared with patients with normal LDH levels (27.6 months vs. 68.8 months; HR, 2.51, 95% CI, 1.88-3.36; P < .001). Survival rates at 5 years in the LDH-normal and LDH-high group were 53.7% and 22.5%, respectively. In the stratified analysis, cohort 1 (25.0 months vs. 63.6 months; HR, 2.41, 95% CI, 1.72-3.39; P < .001) and cohort 2 (27.8 months vs. not reached; HR, 3.16, 95% CI, 1.75-5.70; P < .001) demonstrated similar results as the pooled cohort (Fig. 1).
On the other hand, patients with elevated LDH had significantly shorter RFS (8.5 months vs. 22.0 months; HR, 2.11, 95% CI, 1.54-2.89; P < .001) than patients with normal LDH levels in cohort 1 (Supplementary Fig. 1).
Subgroup analyses revealed that LDH produced consistent prognostic value across patient subgroups stratified by age, sex, primary tumor characteristics (location, T and N stage), liver metastases characteristics (number, maximum diameter, surgical margin, disease-free interval from primary tumor, extrahepatic disease), perioperative chemotherapy, preoperative CEA and CA19-9 levels, even by Fong score. The forest plots provided a clear trend that patients with lower LDH levels obtained better survival benefit from hepatectomy for OS (Fig. 2).
Survival outcomes assessed by CRS, LDH-CRS and mCRS
OS stratified by different risk scores as defined by CRS and LDH-CRS were demonstrated by Kaplan-Meier curves in the pooled cohort. Median OS of the risk scores 0-5 in the CRS model was not reached, not reached, 64.5 months, 41.8 months, 27.6 months, 44.8 months, respectively. Median OS of risk scores 0-6 in the LDH-CRS model were not reached, not reached, 77.6 months, 41.6 months, 41.8 months, 24.2 months, 27.5 months, respectively. While median OS of the risk scores 0-5 in the mCRS model were not reached, not reached, 77.6 months, 39.5 months, 24.2 months, 27.5 months, respectively.
Particularly, LDH-CRS and mCRS identified a relatively higher proportion of patients in the high-risk group (score of 4-6) than CRS (13.2% [67/506] vs. 12.0% [63/526] vs. 8.5% [43/506]). Moreover, the median OS of patients in the high-risk group was numerically shorter in mCRS than in LDH-CRS and CRS (21.8 months vs. 27.8 months vs. 27.8 months) (Fig. 3).
Receiver operating characteristic (ROC) analysis for the comparison of CRS and LDH-CRS in prediction ability
Time-dependent ROC analysis displayed that LDH-CRS and mCRS exhibited a better predictive value than CRS in the pooled cohort for OS (P = 0.016). In the CRS model, the C-index of the 5-year OS probability forecast was 0.653±0.029, the c-index of the LDH-CRS model was 0.674±0.029, while the c-index of the mCRS model was 0.681±0.028 (Fig. 4). These results suggest that adding LDH to the CRS scoring system demonstrated a better accuracy.
Association of LDH levels and immune/inflammation‑related indexes
In an exploratory analysis, it is interesting to note that LDH levels varied with a set of immune/inflammatory factors (Fig. 5). Specifically, patients with elevated LDH had higher preoperative neutrophil counts (P = 0.031), higher C-reaction protein (CRP) levels (P < .001), and lower lymphocyte counts (P = 0.022) than patients with normal LDH levels. Consequently, patients with elevated LDH also had a lower lymphocyte-to-monocyte ratio (LMR; P < .001) and lymphocyte-to-neutrophil ratio (LNR; P < .001). On the contrary, LDH levels were not associated with preoperative total white blood cell counts or monocyte counts.