Patient characteristics
In the training cohort, 229 patients (153 male, 76 females; median age, 40 years [range 18-79]) met the inclusion criteria. Clinical features for all patients are summarized in Table 1. Fifty-seven patients (24.9%) presented with B symptoms. Most of the patients (132 cases, 57.6%) had advanced disease (Ann Arbor stages III-IV). A total of 107 patients had more than one extranodal involvement. According to the IPI score, a majority of the patients (137 cases, 59.8%) were classified as high/ high-intermediate/ low-intermediate risk (IPI=2-5), and 92 patients (40.2%) were categorized as low risk (IPI = 0-1). The number of patients with high-risk stratification (153 cases, 66.8%) was significantly higher than those with low-risk stratification (76 cases, 33.2%). A total of 152 patients (66.4%) received CODOX-M (cyclophosphamide, vincristine, doxorubicin, high-dose methotrexate) based first-line chemotherapy, and 25 patients (10.9%) had received EPOCH (etoposide, prednisolone, doxorubicin, cyclophosphamide and vincristine) chemotherapy. Twenty-eight patients (12.2%) were treated with CHOP (cyclophosphamide, vincristine, doxorubicin and prednisolone) and high dose methotrexate-based regimens, 17 patients (7.4%) received Hyper CVAD (cyclophosphamide, doxorubicin, vincristine and dexamethasone) as first line chemotherapy, and 7 patients (3.1%) were treated with miscellaneous anthracycline-based regimens. Twenty-nine patients (12.7%) and 9 patients (3.9%) had received radiation therapy and autologous hematopoietic stem cell transplantation (ASCT), respectively. Details are shown in Table 1.
Determination of cut-off values for serum markers
The ROC was used to identify optimal cut-off values for indexes. The area under the curve is presented in Table 2. The optimal cut-off values of CRP and albumin levels were 10mg/L and 40mg/L, respectively. By analyzing the specificity and sensitivity of each value, the optimal cutoff values of d-NLR, PLT and LDH were taken as 1.63, 254×109/L and 334 U/L, respectively. Thus, patients were dichotomized into 2 categories: less than, and greater than or equal to the cut-off values.
Univariate analysis and multivariate analysis
Table 3 shows the results of univariate analysis of clinical variables considered predictors of OS. The following clinical factors significantly predicted poor survival in univariate analysis: ECOG≥2, bone marrow involvement, more than two extranodal involvement sites, advanced Ann Arbor stage (III/IV), IPI score≥2, high risk stratification, without CRP≥10mg/L, ALB<40g/L, LDH≥334 U/L, PLT<254×109/L, and d-NLR<1.6. The univariate survival analysis for OS according to optimal cut-off values of ALB, LDH, PLT, d-NLR, CRP, IPI score, Ann Arbor stage, and risk stratification is shown in Figure 1. Multivariate analysis was performed on clinical parameters related to shorter OS. We found that three variables maintained a negative prognostic influence on OS by using forward conditional Cox regression: ALB<40g/L (P =0.041, hazard ratio(HR), 2.251; 95% CI, 1.034-4.902), LDH≥334 U/L (P <0.001, HR, 0.199; 95% CI, 0.081-0.488), and PLT<254×109/L (P =0.038, HR, 2.261; 95% CI, 1.047-4.886) (Table 3).
Prognostic modelconstruction and survival analysis
Consequently, based on these 3 independent prediction factors (ALB<40g/L, PLT<254×109/L, and LDH≥334 U/L) for OS in the multivariate analysis, a new prognostic model for all 229 patients was constructed by combining factors as follows: Group 1 (135 cases, 59%), no more than one adverse factor; Group 2 (60 cases, 26.2%) two adverse factors; and Group 3 (34 cases, 14.8%), three adverse factors. (Figure 2A). The new predictive model for BL effectively stratified patients by prognosis. The median OS of Group 1 and Group 2 was not reached, while the median OS in Group 3 was 17 months. The 5-year survival rates of Group 1, 2 and 3 were 88.1%, 72.4%, and 45%, respectively (P<0.0001). In the subgroup analysis for high-risk and low-risk patients (Figure 2B and 2C), our prognostic model results showed that the high-risk patients with no more than one adverse factor presented a 5-year survival rate of 85.9%, but patients with three adverse factors in high-risk group revealed a 5-year survival rate of 43.0% (P<0.0001). No significant difference was shown in low-risk patients (Figure 2C). The C-index is 0.768 (95%CI 0.705-0.830). According to the IPI score, low-and low-intermediate risk patients could not be distinguished (P=0.8889) (Figure 2D). Low-risk and intermediate-risk patients were also not distinguished based on BL-IPI score (P=0.5045) (Figure 2E).
External validation and survival prediction
To validate our novel prognostic model, 107 patients from another four cancer centers were included. The characteristics of these patients are shown in Table 1. There was good consistency between the validation cohort and the training cohort. Three risk groups could also be predicted using the nomogram, and the 5-year survival rates of Groups 1, 2 and 3 were 90.5%, 77.2%, and 42.9%, respectively (P<0.0001) (Figure 3A). In the subgroup analysis for high-risk patients (Figure 3B), our prognostic model showed that the high-risk patients with no more than one adverse factor presented a 5-year survival rate of 87.1%, but patients with three adverse factors in the high-risk group revealed a 5-year survival rate of 38.9% (P=0.0013). The C-index is 0.806 (95%CI 0.727-0.887).