In the present study, we investigated the impact of chemotherapy-associated neutrophil/lymphocyte counts on prognosis of CRC receiving adjuvant chemotherapy. We found chemotherapy-associated lymphopenia, but not neutropenia to be associated with CRC recurrence, death after adjuvant chemotherapy. The best lymphopenic cut-off affecting CRC recurrence was 0.66 × 109/L, and that affecting CRC death was 0.91 × 109/L. Chemotherapy-associated lymphopenia <0.66 × 109/L/0.91 × 109/L was the independent prognostic factor for worse DFS/OS, respectively, in stage II and III CRC receiving adjuvant chemotherapy. Pretreatment CEA ≥10 ng ml-1 was the independent risk factor for chemotherapy-associated lymphopenia <0.66 × 109/L, and age >60 years was the independent risk factor for chemotherapy-associated lymphopenia <0.91 × 109/L in CRC receiving adjuvant chemotherapy.
It is reported that circulating lymphocytes play a central role in anti-tumor effect. Lymphodepletion due to the altered bone marrow microenvironment was observed in the ApcMin/+ mouse model of intestinal tumorigenesis , which indicates the lymphodepletion may contribute to the drop of anti-tumor immune and tumorigenesis. Due to interplay between soluble factors such as cytokines, chemokines, surface receptors and adhesion molecules, progression and invasion occur in a dynamic microenvironment involving the complex communications between tumor cells and many types of immune cells including the various types of lymphocytes . Thus,lymphopenia is supposed to account for the adverse anti-tumor microenvironment. Moreover, lymphopenia is associated with increased circulating levels of IL-7 [17, 18]. IL-7 plays an oncogenic role promoting proliferation, lymphangiogenesis and metastasis in neoplasm [19–23]. That may partly explain the clinical outcome of chemotherapy-associated lymphopenia in colorectal cancer in our study. Recently, pretreatment peripheral blood lymphocytes have been found to show a significant impact on the complete response rate in response to preoperative radiotherapy in locally advanced rectal cancer (RC) patients and lymphocyte-mediated immune reactions are supposed to have positive roles in radiosensitivity for RC . Likewise, pretreatment lymphopenia is an independent risk factor for shorter survival of palliative chemotherapy in colorectal cancer . Moreover, pretreatment lymphopenia has been found to be the independent risk factor for Peripheral T-cell lymphoma, not otherwise specified (PTCL-NOS) , metastatic breast carcinoma , advanced soft tissue sarcoma  and non-Hodgkin's lymphoma . Lymphopenia is a common adverse event during chemotherapy with the incidence >25% [28, 29]. However, the clinical significance of chemotherapy-associated lymphocyte drop in the adjuvant chemotherapy of CRC is unclear. That indicated lymphopenia, which is the common chemotherapy-induced toxity, may be the possible mechanism for the failure of adjuvant chemotherapy in CRC. Our study also showed chemotherapy-associated neutropenia had no impact on DFS, OS of CRC, suggesting lymphopenia rather than neutropenia may play an important role in the variation of anti-tumor immune reaction during adjuvant chemotherapy in CRC. Chemotherapy-associated lymphopenia is reported rarely in clinical trials. To the best of our knowledge, our study demonstrated the impact of chemotherapy-associated lymphopenia on the clinical outcome of adjuvant chemotherapy in CRC for the first time.
The cut-off of lymphopenia is different in previous studies. Some reports defined lymphopenia as a lymphocyte count of less than 1.5 × 109/L [30–32], while some other reports chose the threshold level of 1.0 × 109/L [25, 27]. However, when we chose the threshold level of 1.0 × 109/L in the present study, lymphopenia <1.0 × 109/L was not the independent risk factor for worse DFS,OS in stage II and III CRC receiving adjuvant chemotherapy(data not shown). Therefore, the cut-offs mentioned above may not be suitable for the evaluation of lymphocyte counts on prognosis of CRC receiving adjuvant chemotherapy. ROC analysis showed the best cut-off of lymphopenia was 0.66 × 109/L for CRC recurrence, <0.91 × 109/L for CRC death in this study and Cox regression model as well as Kaplan–Meier method confirmed the prognostic value of lymphopenia <0.66 × 109/L for DFS,lymphopenia <0.91 × 109/L for OS. Thus, it is reasonable that chemotherapy-associated lymphopenia <0.66 × 109/L/0.91 × 109/L is a simple biomarker affecting worse DFS/OS,respectively, for stage II and III CRC receiving adjuvant chemotherapy. Lymphopenia <0.66 × 109/L/0.91 × 109/L can be the cut-offs to guide the individualized medicine in adjuvant chemotherapy of colorectal cancer.
Moreover, though chemotherapy associated lymphopenia <0.66 × 109/L/0.91 × 109/L showed a longer duration of duration of lymphopenia <1.0 × 109 L compared with lymphopenia ≥0.66 × 109/L/0.91 × 109/L (80.76 ± 49.64 days vs 7.43 ± 12.38 days, 51.84 ± 43.79 days vs 1.43 ± 5.01 days, respectively, data not shown), cox regression model showed lymphopenia <0.66 × 109/L/0.91 × 109/L, but not duration of lymphopenia <1.0 × 109 L, was the independent prognostic factor. That suggest chemotherapy-associated lymphopenia level, rather than duration of lymphopenia <1.0 × 109/L, may play an important role in the prognosis of CRC receiving adjuvant chemotherapy.
The previous studies reported lymphopenia could be affected by various factors including vitamin D deficiency , weight loss , variation of circulating metal ions levels , malnutrition . However, our study showed pretreatment CEA ≥10 ng ml-1 was the only independent risk factor for chemotherapy-associated lymphopenia <0.66 × 109/L, and age >60 years was the only independent risk factor for chemotherapy-associated lymphopenia <0.91 × 109/L in colorectal cancer, suggesting those who have a pretreatment CEA ≥10 ng ml-1 are predispose to lymphopenia <0.66 × 109/L, meanwhile those >60 years old are predispose to lymphopenia <0.91 × 109/L during adjuvant chemotherapy. Thus, pretreatment CEA ≥10 ng ml-1 and age > 60 years should be taken into account in the individualized medicine in adjuvant chemotherapy of CRC to reduce the risk of chemotherapy-associated lymphopenia and improve survival. The rate of grade 3/4 neutropenia in our study was lower than that in the MOSAIC study (41.1%) . In MOSAIC study, FOLFOX was administered to those who have neutrophil counts >1.5 × 109/L, while those with baseline neutrophil counts ≥ 2.0 × 109 cells/L were included in our study. That may contribute to the difference in the severity of neutropenia.
However, there are some limitations in the present study. The sample size was relatively small. Therefore the conclusions, such as the cut-offs of lymphopenia, should be proven by the larger, multicenter study. We also await the further functional analyses of circulating lymphocyte subpopulations that contribute to prognosis of CRC receiving adjuvant chemotherapy.