The study population consisted of patients undergoing surgery for colorectal carcinoma at the Division of General Surgery A, University of Verona Hospital Trust, between January 2005 and December 2012. The inclusion criteria were age of 18 years or older, histological diagnosis of cancer, elective or urgent colorectal resection with absence of peritonitis or other acute infectious diseases, no pre-operative chemotherapy or radiotherapy, follow-up available for a minimum period of 30 mo, as well as preoperative assessment of fibrinogen levels. Informed consent was obtained from all the patients, and the study was approved by the local Ethics Committee with ID number: 42763 (CRINF-1034 CESC).

Between January 2005 and December 2012, 969 patients underwent surgery for colorectal carcinoma at the Division of General Surgery A, University of Verona Hospital Trust. Among them, 652 patients met the inclusion criteria and were enrolled in the study.

Before surgery, all elective patients underwent preoperative staging by means of colonoscopy, thoracoabdominal CT scan and tumour markers (CEA, CA 19-9). Abdominal US was performed in selected cases when a CT scan was deemed unnecessary, whilst additional imaging modalities (e.g., MRI, PET-CT, endoluminal US, etc.) were used when indicated (e.g., rectal cancer or liver metastases). The preoperative assessment of urgent cases varied depending on clinical necessities.

All patients underwent preoperative routine laboratory tests, including coagulation profiles with assessment of plasma fibrinogen levels within two weeks of surgery.

The resected specimens were examined using routine histopathological analysis. Tumour staging was assessed according to the criteria established by the 7^th Edition of the American Joint Committee on Cancer and the Union International Contre Le Cancer. Tumour differentiation; lymphatic, vascular and neural invasion; and inflammatory reactions were generally reported.

Blood samples were drawn by an expert phlebotomist in evacuated blood tubes containing 0.109 mol/L buffered sodium citrate (Terumo Europe NV, Leuven, Belgium). The blood tubes were left in an upright position at room temperature to allow complete blood stability and then centrifuged at 1500 ×g for 15 min. A second centrifugation was performed to obtain platelet-poor plasma, which was stored in aliquots at -70 °C until measurement. At the time of measurement, the plasma aliquots were thawed in a water bath at 37 °C and then left at room temperature for 1 hour. Fibrinogen was measured on an ACL TOP instrument (Instrumentation Laboratory, Milan, Italy) with the Clauss method and using proprietary reagents (HemosIL^® Fibrinogen-C, Instrumentation Laboratory). The reference range of fibrinogen was 200-400 mg/dL

The main goal of the surgery was the complete removal of the tumour (R0 resection), although palliative surgery was carried out in select cases to treat tumour-related complications. The extent of surgery was assessed considering the patient’s performance status, tumour location and stage. Standard colorectal resection (i.e., right hemicolectomy, extended right hemicolectomy, left hemicolectomy, anterior resection, low anterior resection, or abdominoperineal resection) with ligation of vessels at their origin was usually carried out to obtain the optimal management of nodal disease[17], whereas limited colonic resection or stoma formation was performed in select cases (i.e., palliative surgery, high-risk patients).

All clinical and pathological data were retrospectively collected and stored in a digital dataset. The analysed variables included demographic, clinical, surgical and pathological characteristics. Survival and follow-up data were obtained by collecting outpatient clinical records or by contacting the patient or the family physician.

In the preliminary analysis, preoperative fibrinogen levels were normally distributed in the patient cohort. Different cut-off levels were considered to study the potential correlation with clinicopathological factors and survival. The upper limit of the reference range (i.e., 400 mg/dL) was used as the predictive threshold.

To evaluate the significance of difference between cases with values above or below 400 mg/dL, a chi-square test or Fisher’s exact test were used for categorical data and Student’s t-test was used for continuous variables. Survival analysis was computed using the Kaplan-Meier method and compared by the log-rank test, with time of survival measured from the date of surgery to the date of death or most recent follow-up. Multivariate analysis was performed with the Cox regression model by taking into account the following risk factors: age (higher than median vs median or below), gender (male vs female), tumour location (rectum vs colon), type of surgery (urgent vs. elective), presence of residual tumour (R1, R2 vs R0), presence of systemic metastasis (M1a, M1b vs M0), pT category (pT2, pT3, pT4a, pT4b vs pT1), pN category (pN1, pN2 vs pN0), histological type (mucinous vs non-mucinous) and pre-operative fibrinogen plasma levels (fibrinogen value higher than 400 mg/dL vs fibrinogen value lower than this threshold). Statistical analysis was performed using SPSS software version 21.0 (IBM Corporation, Armonk, NY, United States), and the level of statistical significance was set at P < 0.05.

The preoperative mean ± SD of fibrinogen was 426.2 ± 23.2 mg/dL (median: 409 mg/dL; range: 143-1045 mg/dL). Among the 652 patients, the fibrinogen value was higher than the threshold of 400 mg/dL in 345 patients (53%).

Mean ± SD preoperative fibrinogen plasma levels for the 652 patients under study according to their clinicopathological variables are reported in Table 1. Fibrinogen value correlated with age (P = 0.003), type of resection (potentially curative vs palliative) (P < 0.001), presence of systemic metastasis (P < 0.001), CEA serum level (P < 0.001) as well as the pT (P < 0.001) and pN categories (P = 0.001).

Considering histological characteristics, patients with a mucinous histological type (n = 113) displayed higher fibrinogen values compared to non-mucinous histological types (467.1 ± 135.9 vs 417.6 ± 118.7; P < 0.001). The mean ± SD was 395.6 ± 120.4 mg/dL in G1 tumours, 424.1 ± 121.4 mg/dL in G2 tumours and 453.4 ± 131.6 mg/dL in G3 tumours (P = 0.045). Conversely, vascular invasion (P = 0.204), lymphatic invasion (P = 0.940), neural invasion (P = 0.183) and presence of inflammatory reaction (P = 0.067) were not significantly associated with preoperative fibrinogen plasma levels.

Considering the fibrinogen cut-off value of 400 mg/dL, a significant association was found with age (P = 0.001), type of resection (P < 0.001), depth of tumour invasion (P < 0.001), the presence of systemic metastases (P = 0.001), histological type (P = 0.001) and CEA serum level (P < 0.001). Interestingly, fibrinogen values were found to be > 400 mg/dL in 74.2% of patients with macroscopic residual tumours after resection (R2) compared to 49.5% of potentially curative resections (R0) (P < 0.001). Similarly, fibrinogen values were found to be > 400 mg/dL in 71.4% of M1b patients compared to 65.2% of M1a patients and 49.6% of M0 patients (P = 0.001). Regarding the depth of tumour invasion, fibrinogen values were > 400 mg/dL in 32.6% of pT1 patients, 37.7% of pT2 patients, 54.8% of pT3 patients and 61.1% of pT4 patients (P < 0.001). Conversely, the extent of nodal involvement did not correlate with fibrinogen value. Fibrinogen plasma levels were found to be > 400 mg/dL in 50.3% of pN0 patients, 51.8% of pN1 patients and 61.8% of pN2 patients (P = 0.017).

The 5-year survival and 5-year tumour-related survival rates of the study population were 64.4% and 75.2%, respectively. Five-year survival and 5-year tumour-related survival rates according to preoperative fibrinogen plasma levels are shown in Figure 1A. The 5-year survival rate was 72.4% for patients with values ≤ 400 mg/dL and 58.1% for patients with values > 400 mg/dL (P < 0.001). When considering tumour-related mortality, the 5-year survival rate was 81.2% for patients with values ≤ 400 mg/dL and 69.6% for patients with values > 400 mg/dL (P < 0.001).

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Figure 1 Kaplan-Meier estimates. A: Kaplan-Meier estimates of overall survival according to fibrinogen plasma levels in the 652 patients enrolled in the study; B: Kaplan-Meier estimates of tumour-related survival according to fibrinogen plasma levels in the 652 patients enrolled in the study; C: Kaplan-Meier estimates of overall survival according to fibrinogen plasma levels in the 556 R0 patients enrolled in the study; D: Kaplan-Meier estimates of tumour-related survival according to fibrinogen plasma levels in the 556 R0 patients enrolled in the study.

Survival curves for patients undergoing potentially curative resection (R0) are shown in Figure 1B. Fibrinogen plasma levels were associated with overall survival (P = 0.010), whereas no significant difference was observed when tumour-related survival was considered (P = 0.604). In particular, 5-year tumour-related survival was 88.3% in patients with values ≤ 400 mg/dL and 88.7% for patients with values > 400 mg/dL.

Table 2 shows the multivariate analysis (Cox regression model) adjusted for multiple factors. Age, the presence of systemic metastasis, the presence of residual tumour, pT category and pN category were confirmed as independent predictors of survival, whereas the fibrinogen plasma level was not [hazard ratio (HR) for fibrinogen value > 400 mg/dL compared to ≤ 400 mg/dL: 1.15 (95%CI: 0.86-1.54), P = 0.355]. Similar results were found for tumour-related survival [HR for fibrinogen value > 400 mg/dL compared to ≤ 400 mg/dL: 0.82 (95%CI: 0.54-1.21), P = 0.313]. Table 3 shows 5-year survival and tumour-related survival rates for Stage I, Stage II, Stage III and Stage IV tumours treated by potentially curative resection (R0).

Fibrinogen is involved in tumourigenesis as well as tumour progression in several malignancies. Previous studies have shown hyperfibrinogenemia to be correlated with main clinicopathological characteristics and prognosis after colorectal cancer surgery. Nonetheless, the effective clinical significance of preoperative plasma fibrinogen levels as a prognostic marker after colorectal cancer surgery has not yet been determined.

This study represents the first analysis of the value of preoperative fibrinogen plasma level in a Western population and one of the largest cohort of patients.

This study based on a large Western cohort did not confirm hyperfibrinogenemia to be an independent prognostic factor in colorectal cancer patients.

Evaluation of fibrinogen plasma levels are routinely perform among preoperative blood tests. Its correlation with leading prognostic factors in patients undergoing surgery for colorectal cancer (CRC) is interesting and require further studies.

CRC is the third most common cancer worldwide. CRC is associated with a large range of fibrinolytic and procoagulant alterations and fibrinogen plasma levels could represent the expression of this relationship.

This paper tried to elucidate role of fibrinogen plasma level in the prediction of CRC prognosis. The manuscript is well written and the data and table are clear.