Platelet Indices in Colorectal Cancer Patients with Synchronous Liver Metastases

Aims Liver metastases occur in approximately 25% of colorectal cancer (CRC) patients and cause more than 90% of deaths in CRC. Platelets play a crucial role in cancer progression and metastases. We aimed to investigate the relationship between platelet indices and CRC with synchronous liver metastases. Methods We conducted a retrospective clinical study including 206 CRC patients without metastases and 200 CRC patients with synchronous liver metastases from January 1, 2015, to December 31, 2017. Data of the patients' clinicopathological characteristics were collected. Results Platelet distribution width (PDW) was decreased in CRC patients with liver metastases compared with CRC patients without liver metastases. In addition, the prevalence of liver metastases reduced as PDW quartiles increased. After adjusting for other risk factors, the odds ratios (95% confidence intervals) for CRC liver metastases according to PDW quartiles were 1.000, 0.289 (0.156-0.535), 0.482 (0.271-0.860), and 0.190 (0.101-0.358). Conclusions Compared with CRC patients without metastases, PDW is reduced in CRC patients with liver metastases. Moreover, PDW was independently associated with the presence of CRC liver metastases.


Introduction
Liver metastases occur in approximately 25% of colorectal cancer (CRC) patients and cause more than 90% of deaths in CRC [1]. CRC patients with liver metastases have an estimated 5-year survival of 38% [2]. Therefore, identification of novel serum biomarkers for CRC with liver metastases is urgently needed.
Platelets act as a crucial role in tumor growth and metastasis [3,4]. Mean platelet volume (MPV) reflects platelet size and indicates platelet activation in clinical practice [5]. Platelet distribution width (PDW) reflects variation in platelet size and differentiates thrombocytopenia [6]. MPV was found to be altered in numerous tumors, such as lung, breast, gastric, ovarian, and colorectal cancers [7][8][9][10][11]. Our previous study also revealed that elevated MPV predicts a worse prognosis in CRC patients [12]. However, there is no study investigating the clinical implications of platelet indices in metastatic CRC patients.
We aimed to evaluate the relationship between platelet indices and CRC with liver metastases.

Study population.
From January 2015 to December 2017, 200 CRC patients with synchronous liver metastases and 206 CRC patients without metastases at the Harbin Medical University Cancer Hospital were included in this study. CRC was histologically diagnosed. CRC synchronous liver metastases were defined as liver metastases detected at or before diagnosis of CRC [13]. Liver metastases were assessed with liver magnetic resonance imaging (MRI). All patients received MRI scanning of the head, CT lung screening, liver MRI, and 99m Tc-MDP bone scan. The exclusion criteria were the following: (1) underwent radiotherapy or chemotherapy prior to the enrolment, (2) had hematological disorders, (3) administration of acetylic salicylic acid, and (4) had other organ metastasis besides the liver.
The study was approved by the institutional review boards of Harbin Medical University Cancer Hospital. The informed consent was waived because this was a retrospective study.

Statistical
Analysis. Student's t-test (for continuous variables with normal distribution), Mann-Whitney U test (for continuous variables with nonnormal distribution), and χ 2 test (for categorical variables) were used to analyze the differences between two groups. Multivariate logistic regression analysis was used to calculate the odds ratios and 95% confidence intervals for liver metastasis adjusting for other confounding factors. P < 0:05 was considered statistically significant. All analyses were performed by using SPSS Statistics version 22.0 (SPSS Inc., Chicago, IL, USA). Table 1 summarizes the clinicopathological characteristics of CRC patients. Of the 406 CRC patients enrolled, 236 (58.1%) were men and 170 (41.9%) were women. The patients with liver metastasis had a lower albumin, haemoglobin, and PDW and higher white blood cell counts. The number of patients with poor differentiation was 48 and 56 in the metastasis and nonmetastasis groups, respectively. However, statistical significances were not found in age, gender, smoking status, drinking status, fasting plasma glucose, platelet count, and MPV levels between two groups.

Results
The platelet indices in CRC patients were shown in Table 2 and Table 3. In the group of nonliver metastasis, platelet count was significantly associated with T stage. MPV was associated with tumor size and PDW with lymph node metastasis. In the group with liver metastasis, we failed to observe the associations between platelet indices and primary tumor location, tumor size, differentiation, T classification, lymph node metastasis, metastatic tumor size, and metastatic tumor nodules. The ROC curve for metastasis was used to verify the optimum cutoff points for PDW. A PDW ≤ 16:5% was shown to be predictive for CRC liver metastasis, with a sensitivity of 51.0% and a specificity of 85.2% (area under the curve 0.712; 95% confidence interval 0.659-0.766; P < 0:001).
The risks of liver metastasis according to PDW quartiles are analyzed and shown in Table 4. After adjusting for age, gender, BMI, smoking status, drinking status, WBC, haemoglobin, albumin, and fasting plasma glucose, the prevalence

Discussion
Our study demonstrated that the CRC patients with liver metastases have lower PDW levels compared to those without metastases and PDW was independently associated with the presence of liver metastases. The interaction of tumor cells with platelets leads to platelet activation, which in turn promotes tumor progression and metastasis [14]. Elevated platelet-derived growth factor D promotes CRC cell proliferation and invasion by upregulating the expression of Notch1 and matrix metalloproteinase 9 [15]. Moreover, platelet-derived endothelial cell growth factor levels were increased in CRC patients and were associated with poor prognosis [16,17]. A recent study confirmed that serum platelet-derived growth factor AA is an independent predictor for CRC liver metastasis [18]. In addition, the use of low-dose aspirin could restore antitumor activity by inhibiting platelet COX-1 [19]. Our study confirmed the important role of platelet activation in CRC. Moreover, our results provide the basis for applying antiplatelet therapy in CRC patients with liver metastases.
The mechanisms underlying the association between reduced PDW and CRC liver metastases remain unclear. The interaction between platelets and tumor cells induces cell plasticity and promotes cancer metastasis by enhancing circulating tumor cell survival and extravasation [20]. PDW is an indicator of the average change in platelet volume. Platelet volume is determined both during megakaryopoiesis and thrombopoiesis. The decrease of PDW reflects the failure of heterogenic megakaryocytic maturation [21]. The thrombocytopoiesis is regulated by many factors, among which the key factor has been attributed to thrombopoietin (TPO) [22]. Elevated plasma TPO levels have been observed in cancer patients with advanced stage [23]. Recent study found that PDW was a better indicator to reflect the characteristics of activated platelets [24]. The secretory factors released by activated platelets promote the expression of cytokines, proteolytic enzymes, and chemokines within the microenvironment and accelerate cancer invasion [25]. Overexpression of platelet-derived growth factor (PDGF) was related to uncontrolled angiogenesis in CRC patients with liver metastases and was found to be a new prognostic indicator for a worse prognosis in CRC [18,26]. In addition, overexpression of PDGF receptor is associated with advanced stage disease in stromal cells of human colon carcinomas [27]. In addition, recent studies revealed that dual antiplatelet therapy (aspirin and clopidogrel) inhibits the expression of α-granule-stored proteins and decreases the heterotypic interactions between platelets/leukocytes and the endothelium [28].
Our current study bears several limitations. Firstly, it was a retrospective and single center study. Secondly, the mechanisms underlying the association are needed to clarify. Thirdly, the conclusion could not be applied to other ethnic groups because the cohorts in our study were composed of Chinese patients.
In summary, compared with CRC patients without metastases, PDW is reduced in CRC patients with liver metastases. Moreover, PDW was independently associated with the presence of CRC liver metastases.

Data Availability
The data used to support the findings of this study are available from the corresponding authors upon request.

Ethical Approval
The study was approved by the institutional review boards of Harbin Medical University Cancer Hospital.

Conflicts of Interest
The authors declare that they have no conflicts of interest.