The values of applying classification and counts of white blood cells to the prognostic evaluation of resectable gastric cancers

Gastric cancer (GC) is the fourth most common cancer in the world and the second essential factor to death of cancers [1, 2]. According to the cancer statistics in 2017, new gastric cancer cases numbered almost 28,000, and more than 10,960 deaths were caused by gastric cancer in united states [2]. Although both the lethality and morbidity of GC have decreased in recent years, the 5-year survival rate remains quite low still [3]. Therefore, it is important to identify reliable predictive factors for the prognosis of GC patients.

Total white blood cell (WBC) count which is often elevated during infections, is one of the nonspecific markers of inflammation and can be linked with some particular kinds of cancers [4]. WBC can be divided into five types, including lymphocyte (LY), monocyte (MO), neutrophil (NE), eosinophil (EO), basophil (BA) [5]. LY can respond to the host’s immune response, and low level of LY has been reported in various cancers [6, 7]. MO is produced in the bone marrow and stored in bone marrow, liver, as well as lymph nodes. MO plays critical role in systemic inflammatory response and steady-state immune-surveillance [8]. NE responds to infection and injury [9]. In addition, an elevated count of blood NE has been shown to predict poor survival in advanced GC [10] and esophageal cancer [11]. Besides, Sam C. Wang et al. proved that pretreatment NE to LY ratio independently predicts disease-specific survival in patients with resectable gastroesophageal junction and gastric adenocarcinoma [12]. EO is uncommon in healthy individuals, however, it is associated with allergies, helminth infections and some inflammatory states. Moreover, previous studies have shown a close association between EO level and the prognosis of GC patients [13]. BA, derived from bone marrow, is the rarest granulocytes and occupied less than 1% of peripheral leukocytes [14]. BA is well recognized to play a crucial role in protection against infections with parasites, allergy and autoimmunity [15, 16].

The present study investigated whether the classification and counts of WBCs can be served as prognostic indicators in patients with the resectable GC.

To date, many studies have reported the relationship between the elevated total WBC count and cancer risks. Thomas P. Erlinger et al. proved that WBC is associated with total cancer mortality after adjustment for age, sex and race [17]. Yong-Jae Lee and colleagues identified that increased WBC count was associated with a higher mortality and incidence risk of colon cancer [18]. Masahiro Lida et al. found that the incidence of GC increased linearly with increasing count of total WBC [19]. Moreover, total WBC count was negatively related to the survival of GC, especially with H. pylori (HP) infection [19]. H. pylori infection has been shown to increase the production of reactive oxygen metabolites [20, 21], which often cause extensive tissue damage and DNA damage, leading to mutations of oncogenes and tumor suppressors [22, 23]. Therefore, the relationship between total WBC count and survival of GC could be a reflection of the extent of mucosal inflammation induced by H. pylori infection [24]. In our present study, we found that higher pre-treatment total WBC status was associated with worse OS, in consisting with previous studies. Univariate analysis demonstrated that higher pre-treatment total WBC count was a significant risk factors and multivariate analysis demonstrated that total WBC count was an independent prognostic marker for a poor prognosis. However, neither surgery nor adjuvant chemotherapy could affect total WBC count. Post/pre-treatment ratio of total WBC had no significant effects on OS either.

Previous studies have confirmed that peripheral blood LY count is an independent prognostic factor for multiple cancers, such as breast [25], pancreatic [26], lung [27], cervical [28] and gallbladder cancers [29]. In cell-mediated anti-tumor immune response, LY has a crucial role in many cancers [30, 31]. Tumor-infiltrating lymphocytes (TILs) have a positive effect on OS in colorectal and ovarian cancers [32, 33], which may due to the apoptosis induced by tumor cells and the activation of specific CD8+ T cells. In addition, CD4+ T lymphocytes play a key role by secreting cytokines such as IL-2, which is required for CD8+ T lymphocytes proliferation and growth. Previous studies indicated that, activation of CD4+ T cells are required for immunization of CD8+ T cells against cancer [34]. However, in the present study, we found that LY count was not associated with OS in resectable GC patients.

Inflammation-induced carcinogenesis is caused by several processes, including genotoxicity, aberrant tissue repair, proliferation, invasion and metastasis [35]. MO, as a marker of systemic inflammatory response, may thus be a predictive factor for various inflammation-related cancers. In many previous studies, MO has been proved to be negatively related to OS of tumor patients, such as pancreatic cancer and hepatocellular carcinoma [36, 37]. Multiple mechanisms might be involved in the relationship between MO and tumor prognosis. As mentioned above, the inflammatory response has laid an important foundation in the development of cancer. MO, as an important component of the adaptive and innate immune system, can both facilitate angiogenesis and tumorigenesis. MO can also secret soluble mediators and promote the growth of cancer [38]. In addition, Evani et al. found that MO can promote proliferation of breast cancer by improving adhesion of tumor cells [39]. Besides, MO can differentiate into tumor-associated macrophage (TAM), which plays a major part in tumor microenvironment through promoting tumor progression, metastasis, angiogenesis, migration and immune escape [40]. However, in our present study, neither surgery nor adjuvant chemotherapy had significant effects on MO count. In addition, pre-treatment or post/pre-treatment ratio of MO had no effects on OS, either.

Chronic inflammation is essential for cancer growth and metastasis. NE is one of the well-known marker of systemic inflammatory response. Increasing evidences show that it is also a predictor of poor prognosis in a variety of malignant tumors [10, 11, 41, 42]. It has been reported that activation of endogenous or exogenous pathways could mobilize transcription factors and inflammatory mediators, which may led to recruitment of inflammatory cells, including NE [43]. In our present study, we found that NE count could be down-regulated by surgery. In addition, pre-treatment NE count was negatively related to OS, and univariate analysis indicated that higher pre-treatment NE count was a significant risk factors for a poor prognosis. Basing on changes in individual NE count levels, post/pre-treatment ratio of NE had no significant effects on OS.

Higher EO count has been observed in several malignant tumors, such as colorectal [44], breast [45], cervical [46], oral squamous [47] and prostate cancers [48]. The relationship between EO and prognosis is still indefinite. In colorectal and prostate cancers, EO infiltration has been linked to a favourable prognosis [44, 48]. However, EO appears to be an independent and significant unfavorable prognostic factor in adult T cell leukaemia/lymphoma, chronic eosinophilic leukemia and Hodgkin’s lymphoma [49‐51]. The growth-promoting effect EO could be executed through secreting several pro-angiogenic factors, including VEGF, fibroblast growth factor-2, and IL-8 [52]. Our present study revealed that surgery increased the level of EO count. However, neither pre-treatment level nor post/pre-treatment ratio of EO count was related to the prognosis of resectable GC patients.

Researches on the functions of BA were hindered by their rarity, difficulty in identifying, and lack of useful analytical tools [14]. Existing researches have focused on the role of BA playing in parasite allergy, immediate hypersensitivity and autoimmunity [16]. Moreover, as a type of immune cells, BA is demonstrated to be negatively associated with outcomes of pancreatic cancer [53]. Additionally, in a mouse model of metastatic breast cancer by implanting 4 T1 cells into the mammary fat pads, some reseacheres identified that the presence of BA predicted tumor growth. In the present study, chemotherapy down-regulated BA status. While, pre-treatment level and post/pre-therapeutic ratio of BA had no significant effects on OS.Taken together, our present investigation showed that higher pre-treatment level of NE and total WBC counts were correlated with worse prognosis in resectable GC. These noninvasive, simple and low-cost biomarkers may be prognostic indicators. The limitations of our study may include its retrospective design, recruitment of patients from single center, and insufficiency of case number. To eliminate the differences in the general performance of patients, we studied each case thoroughly and excluded patients with chronic diseases such as inflammatory bowel diseases and rheumatic diseases, etc.al. Eventually, only a limited number of 104 cases were obtained. Likely, our results were consistent with the previous studies, and we believed our results were highly reliable. Of course, we would conduct a multi-center study and collect more cases data to further explore the conclusion in the future.

Our study demonstrated that pre-treatment NE and total WBC counts were negatively correlated with overall survival (OS). Surgery significantly decreased the level of NE count, and adjuvant chemotherapy significantly decreased the level of BA. Univariate analysis indicated that AJCC stage (III) and higher level of pre-treatment total WBC count were prognostic factors affecting OS. Multivariate Cox regression analysis revealed that AJCC stage (III) and higher level of pre-treatment total WBC count were independent prognostic factors. Therefore, we suggested that pre-treatment NE count and pre-treatment total WBC count may be potential prognostic factors for the prognostic evaluation of GCs.