ABO blood type correlates with survival in hepatocellular carcinoma following hepatectomy

ABO blood types are associated with the prognosis of several malignancies. However, the role of the ABO blood type in hepatocellular carcinoma (HCC) remains elusive. Here, we evaluated the prognostic role of the ABO blood group in 691 HCC patients after hepatectomy by Cox regression analysis. A prognostic nomogram was generated to predict the 3 and 5-year overall survival (OS). A total of 262 HCC patients (37.9%) had blood group O, 199 (28.8%) had blood group A, 165 (23.9%) had blood group B, and 65 (9.4%) had blood group AB. The median OS was 55 months in patients with blood group O, 39 months for blood group A, 34 months for blood group B, and 34 months for blood group AB patients (P = 0.001, log-rank test). There were significant differences in OS between patients with blood groups O and A [hazard ratio (HR) = 1.416; 95% CI, 1.101–1.820; P = 0.007], blood group B (HR = 1.736; 95% CI, 1.333–2.262; P < 0.001), blood group AB (HR = 1.739; 95% CI, 1.210–2.499; P = 0.003) and non-O blood groups (HR = 1.485; 95% CI, 1.204–1.830; P < 0.001). Our constructed nomogram (c-index = 0.687) predicted the prognosis more accurately than the TNM stage alone(c-index = 0.601). In conclusion, non-O blood groups are poor prognostic indicators for HCC following hepatectomy. Our findings justify further external validation in larger cohorts.

and AB in 65 (9.4%) patients. Patient baseline characteristics were similar across the blood groups except for the AFP level, which was higher in individuals with blood group O(P = 0.014).

Correlation of ABO blood type with survival.
Overall, 392 patients died and 299 survived after a median follow-up of 36 months (IQR, 25-75 months). As shown in Figure 1A, the blood group correlated significantly with OS (P = 0.001  Figure 1B and Table 2, OS was significantly higher in patients with blood type O blood compared with non-O blood types (P < 0.001). Our findings indicated that blood group AB correlated positively with AFP levels. Thus, we further examined the interaction between blood type and AFP level as a predictor of prognosis. As shown in Figure 2, OS differed between patients with non-O and O blood groups subdivided by AFP level. Of note, ABO blood group correlated significantly with OS in HCC patients with high AFP levels (AFP > 400 ng/ ml, P = 0.018), but not in HCC patients with low AFP levels (P = 0.072). Univariate analysis revealed that age (P = 0.044), serum AFP levels (P = 0.008), tumor size (P = 0.001), stage (P < 0.001), differentiation (P < 0.001), and ABO blood group (P = 0.001) were prognostic indicators for overall outcome. Further multivariate analysis identified age, tumor TNM stage and tumor differentiation as significant prognostic factors for OS. In particular, the ABO blood type was a prognostic indicator for OS. The hazard ratio (HR) of patients with blood type A was 1.416 (95% CI, 1.101-1.820, P = 0.007), the HR of patients with blood type B was 1.736 (95% CI, 1.333-2.262, P < 0.001), and the HR of patients with blood type AB was 1.739 (95% CI, 1.210-2.499, P = 0.006), when compared with blood group O. Patients with non-O blood groups had a worse survival (HR = 1.485; 95% CI, 1.204-1.830; P < 0.001). These analyses are presented in Table 3. Figure 3, we used a nomogram to predict the probability of death in individual HCC patients within 3 or 5 years after hepatectomy. Independent prognostic factors (age, tumor stage, differentiation and blood type) were incorporated into the nomogram. Calibration curves are shown in Figure 4, and these were similar to the ideal model. The Harrell's c-index for OS was 0.687, higher than that for the TMN stage alone (0.601), This indicated that the nomogram was able to predict the prognosis more accurately.

Discussion
ABO blood type was recently shown to affect the risk of multiple cancers 18,19 , including HCC 16,17 . Based on these reports, we hypothesized that the ABO blood group is associated with survival in HCC patients.
In the current study, ABO blood group was associated with OS in a large cohort of HCC patients following hepatectomy. The prognosis and overall outcome were worse in HCC patients with non-O blood type compared with blood group O. Interestingly, the ABO blood type did not correlate with OS in HCC patients with low AFP levels. The correlation between blood type and oncologic outcome of HCC has not been investigated so far. Our results are consistent with previous studies in patients with pancreatic cancer 20 , renal cancer and bladder cancer 21,22 . These studies indicated a better prognosis in patients with blood type O compared with non-O blood groups. Prognostic nomograms can evaluate the prognosis in individual patients 23 . In this study, we developed a novel nomogram incorporating ABO blood type and other prognostic factors. Our proposed nomogram was more discriminative than the TNM stage in predicting the prognosis of HCC after liver resection. In addition, our nomogram (model) might facilitate accurate prognostic stratification and the selection of optimal therapies. The serum blood type can easily be determined in all HCC patients and understanding the influence of blood group on tumor biology or therapeutic response may accelerate the development of individualized therapy for HCC.
The mechanisms by which ABO blood type influences HCC patient outcomes remains to be fully elucidated. However, several plausible hypotheses may explain the correlation. The ABO gene contains two alleles (A and B) that encode glycosyltransferases that catalyze the transfer of nucleotide donor sugars to the H antigen, which is then converted into ABO blood group antigens 24 . Aberrant glycosylation is a hallmark of cancer progression 25 . Terada and colleagues 26 reported that ABO antigens are usually expressed in HCC tissue but not in normal liver and chronic hepatitis tissue. This suggests that alterations in glycosyltransferase are involved in HCC carcinogenesis and may explained how blood group affects OS in HCC patients. A correlation has also been reported between ABO blood group and liver disease. Poujol-Robert et al. revealed that individuals with non-O blood groups had an increased risk of liver fibrosis following HCV infection 27 . Moreover, Li et al. reported that non-O blood groups may increase the risk of HCC. Furthermore, a link between ABO and important cytokines has been shown, which may promote the development of HCC 28 . Recent studies have revealed single nucleotide polymorphisms in the ABO locus that correlate with circulating levels of tumor necrosis factor-alpha (TNF-a) and intercellular adhesion molecule-1(ICAM-1) 29,30 . TNF-a is a multifunctional inflammatory cytokine involved in hepatocarcinogenesis. ICAM-1 regulates the immune response, which is implicated in the antigen-presenting mechanism 31 . Serum soluble ICAM-1(sICAM-1) has been associated with occurrence and prognosis of HCC 32 . Interestingly, a recent genomic study demonstrated that sICAM-1 levels are linked to ABO gene variants 33 . Patients with non-O blood groups express low levels of sICAM-1, compared with blood group O 34 , and reduced sICAM-1 levels may promote tumor metastasis in these patients 35 . These biological mechanisms may explain the favorable survival of HCC patients with blood type O. The mechanism underlying the interaction between blood type and AFP level is currently not well understood and should be further explored.
There were limitations to the present study. The major disadvantage of this analysis was its retrospective nature. The study was not representative of the general population and the possibility of selection bias cannot be ruled out. The ABO blood group was analyzed in relation to race, but all participants were Chinese; therefore these findings cannot reliably be extrapolated to other populations. The Eastern Cooperative Oncology Group scores were was not assessed because these data were not available. Furthermore, unidentified confounders may  Table 3. Prognostic factors for overall survival by multivariate analysis. have biased our results. All participants had received a hepatectomy. Therefore, the findings cannot be used to predict associations between blood group and survival of patients with advanced HCC.

Conclusions
In summary, we have shown that ABO blood type is associated with the prognosis of Chinese HCC patients after hepatic resection. OS is reduced in patients with non-O blood types (blood group A, B, and AB) compared with blood type O. Further studies are necessary to confirm these findings and to elucidate the underlying mechanisms.

Patients and Methods
Ethics statements and patients.  Study endpoints and survival data. Outcome data were collected by telephone survey until October 2014 or until patient death. Overall survival (OS) was defined as the time from start of surgery to death from any cause or the last follow-up date. Patients alive at the time of last follow-up were defined as censored data.
Statistical analysis. Categorical variables were compared using the Chi-square test or Fisher exact test.
The cumulative OS was estimated according to the Kaplan-Meier method and tested using the log-rank test. The prognostic value of each factor was determined according to the Cox proportional hazards regression model. Significant prognostic indicators of endpoints in univariate analysis were included in the multivariate analysis.
A nomogram was formulated based on the results of the multivariable analysis. Harrell's c-index and calibration curve were used to assess the performance of the nomogram 36 . These activities were calculated using bootstrapping with 1000 repetitions. The prognostic nomogram were constructed and analyzed by R 3.3.1 with rms packages (http://www.r-project.org). Other statistical analyses were performed using SPSS23.0 software (IBM Corporation, Armonk, NY, USA). Statistical significance was set at P < 0.05.