Association between ABO blood type and type I endometrial cancer: a retrospective study

Abstract This study aimed to assess the association between ABO blood type and incident of type I endometrial cancer (EC), as well as the stage and differentiation. 213 patients with type I EC and 300 healthy controls were included. As a result, the frequencies of A, B, O, and AB blood types among patients with type I EC were 51 (23.9%), 59 (27.7%), 93 (43.7%) and 10 (4.7%), respectively. There were no significant differences in age, body mass index, and other baseline covariates between groups of ABO blood types (p > .05). Logistic regression model showed that women with blood type O was more likely to develop type I EC than those with type A (odds ratio (OR): 1.66, 95% confidence interval (CI): 1.05–2.63). However, there was no significant association of ABO blood type with stage and differentiation of type I EC (p > .05). In conclusion, blood type O was the most prevalent ABO blood type among patients with type I EC and was associated with increased risk of type I EC, while ABO blood type was not significantly associated with stage or differentiation of type I EC. IMPACT STATEMENT What is already known on this subject? Previous studies have produced inconsistent findings on association of ABO blood type with EC. Those studies also did not explore the relationship between ABO blood type and stage or differentiation of type I EC. What the results of this study add? The present study showed that women with blood type O was more likely to develop type I EC than those with type A and there was no significant association of ABO blood type with stage or differentiation of type I EC. What the implications are of these findings for clinical practice and/or further research? Gynaecologists should pay more attention to women with blood type O, who should undergo more active EC screening.


Introduction
Endometrial cancer (EC) is one of the common gynecological malignancies in both developed and developing countries (Lu and Broaddus 2020, Makker et al. 2021, Sung et al. 2021, Crosbie et al. 2022).There were 417,367 new EC cases and 97,370 cancer deaths worldwide in 2020 (Sung et al. 2021).The incidence and death rates of EC have increased dramatically in the past 20 years and it was diagnosed in about 58,500 women in the United States per year (Lu and Broaddus 2020).Several risk factors are involved in the incident of EC, including old age, obesity, diabetes mellitus, early menarche, and family history of endometrial, ovarian, or colon cancer (Sobel et al. 2021, Hazelwood et al. 2022, Lei et al. 2022).
The ABO gene is located on chromosome 9 (9q34), and contains seven exons that span more than 18 kb of genomic DNA (Hong et al. 2021).This gene encodes glycosyltransferases that catalyse the addition of a single sugar to the H antigen to form the A and B antigens.ABO blood type antigens are not only expressed on the surface of erythrocytes, but also on the surface of epithelial cells such as the digestive tract, skin and genitourinary tract (Abegaz 2021).Therefore, the distribution of blood groups in tumour patients and the normal population can be compared to assess the genetic tendency of tumour (Rummel and Ellsworth 2016).In recent years, many studies have shown that ABO blood types can affect the occurrence and development of various pathogenic processes and may be related to tumour susceptibility (Alexandra et al. 2022), and even Coronavirus Disease 2019 (COVID-19) (Zhao et al. 2021).In 1985, Aird et al. (Giannopoulos et al. 1985) first reported an association between blood type and renal cell carcinoma.Later studies reported the relationship between ABO blood type and various cancers, which suggested that human blood group antigens may affect the incident of cancer (Huang et al. 2017, Bothou et al. 2019, Mao et al. 2019, Song et al. 2019).Furthermore, a genome-wide study found that the ABO gene locus is significantly related to the development of pancreatic cancer (Amundadottir et al. 2009).
However, very limited number of epidemiological studies have examined the association between ABO blood type and EC (Xu et al. 2011, Yuzhalin and Kutikhin 2012, Nakashidze et al. 2014, Abu-Zaid et al. 2017, Gitas et al. 2020).Furthermore, these studies were produced inconsistent findings.To our knowledge, no study has yet investigated the potential contribution of ABO blood groups to the stage and differentiation of type I EC in developing country.Therefore, the aim of this study was to investigate the relationship between ABO blood types and the occurrence, staging, and differentiation of type I EC.

Study design, population and data source
This retrospective study was performed between 1 January 2015 and 31 November 2020 at the Department of Gynaecology of Guangdong Second Provincial General Hospital and included 213 adult patients with pathologically confirmed type I EC.The histopathological classification of all patients was endometrioid carcinoma.Patients with missing blood type (N ¼ 16) or pathological diagnosis (N ¼ 2); those with a history of gynaecologic malignancies, colon cancer, or polycystic ovarian syndrome (N ¼ 11); those undergoing concurrent tamoxifen therapy (N ¼ 3); those with endometrial thickness � 15 mm while on hormone replacement therapy (N ¼ 9), were excluded.Patient-level data were obtained from the electronic health record system, including demographic characteristics, histopathological data, laboratory data, image data and surgery information.We referred to Federation of International of Gynaecologists and Obstetricians (FIGO) 2009 and FIGO 2018 guidelines for surgical staging procedures (Pecorelli 2009, Amant et al. 2018).The recommended basic surgical procedures are extra-fascial total hysterectomy with bilateral salpingo-oophorectomy and laparoscopic procedures.lymphadenectomy is reserved for cases with high-risk features (Obesity, elderly, infertility, long-term application of oestrogen, menstruation, combined with hypertension or diabetes, family history of endometrial cancer, etc.).There were 300 healthy controls who were randomly selected from the Health Examination Centre and were age-and sex-matched to the type I EC cases during the same period.
The study protocol was approved by the Medical Ethics Committee of Guangdong Second Provincial General Hospital, which waived the requirement for patient informed consent due to the retrospective nature of the study.The study was conducted in accordance with the Declaration of Helsinki and was designed following the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement (Von Elm et al. 2007) and Enhancing the Quality and Transparency Of health Research (EQUATOR) reporting guidelines.

Clinical covariates
ABO blood groups were categorised as type A, B, AB, and O.Other clinical covariates included age, body mass index (BMI), platelets, menarche, menstrual cycle, number of childbirth, history of childbirth, hypertension, diabetes, family history of cancer, menopause, perimenopausal, myometrial infiltration, any invasion (including invasion of the cervix, lower uterus, vessels, lymph nodes, nerve and left or right side of the uterus), FIGO staging classification of type I EC (classified as I, II, III, or IV), and tumour differentiation (classified as welldifferentiated [G1, low-grade], moderately differentiated [G2, middle-grade], or poorly differentiated [G3, high-grade] according to FIGO classification) (Pecorelli 2009, Amant et al. 2018).FIGO stage was further divided into early stage (I&II) and advanced stage (III&IV), and tumour differentiation was divided into low-middle grade (G1-2) and high grade (G3) to explore the relationship between ABO blood type and stage or differentiation of type I EC.Because only one person reported a history of smoking and drinking, these two variables were not included in the final analysis.

Statistical analysis
Shapiro-Wilk's normality test and Bartlett test were used to detect the normal distribution and homogeneity of variance of continuous variables, respectively.Continuous variables were presented as the mean ± standard deviation (SD) for normally distributed data compared using One-Way ANOVA or median (interquartile range [IQR]) for data that were not normally distributed compared using Kruskal-Wallis test.Categorical data were presented as number (percentage) and compared using Pearson v 2 test.The risk of EC associated with blood types was estimated using a logistic regression model, which expressed as odds ratios (OR) and 95% confidence intervals (CI).Univariate and multivariate logistic regression models were used to explore the association between ABO blood type and stage or differentiation of EC.
All analyses were performed with a statistical programming language (R, version 4.0.2;R Development Core Team; https:// www.r-project.org/).Statistical significance was determined at the level of 0.05.All p-values were based on two-sided tests.

Characteristics of study population
Among the 213 patients with type I EC included in this study (Figure 1), the frequencies of A, B, O, and AB blood types were 51 (23.9%), 59 (27.7%), 93 (43.7%) and 10 (4.7%), respectively.The majority of type I EC patients had type O blood.The mean age and BMI of the study population were 53.1 ± 8.7 years (range: 27-79) and 24.8 ± 3.9 kg/m 2 (range: 16.8-38.1),respectively.Table 1 showed the demographic and clinical characteristics of the study population.There were no statistically significant differences in age, BMI, pathological type, clinical stage, differentiation degree, and other clinical covariates between groups of ABO blood type (p > .05).The distribution of ABO blood type stratified by EC and healthy controls was shown in Figure 2. Blood type B was the most frequent in the healthy control group, whereas blood type O was the most frequent in the EC patients.Figure 3 showed the distribution of ABO blood type in patients with type I EC stratified by age, BMI, stage and differentiation.The vast majority of patients were older (age >50 years: 60.6%), had BMI <28 kg/m 2 (81.7%), were diagnosed with early FIGO stage I-II (91.5%), and progressed to low-middle grade of differentiation (77.9%).

Surgery information
In our study, all participants with type I EC received a transabdominal or laparoscopic total uterus resection after diagnosis, which was performed laparoscopically in 113 (53.1%) patients and by transabdominal surgery in 100 (46.9%).Detailed surgery information was summarised in Supplemental Table 1.Bilateral adnexectomy was performed in 200 (93.9%)patients, 106 (49.8%) patients received pelvic lymphadenectomy, and only 31 (14.6%)patients received abdominal aorta lymphadenectomy.In addition, 64 (30.0%) patients underwent lysis of pelvic adhesions during surgery.

Association between ABO blood type and type I EC
The logistic regression model showed that women with blood type O had a higher risk of developing type I EC (OR, 1.66; 95% CI, 1.05-2.63)than those with blood type A (Table 2).

Association between ABO blood type and stage or differentiation of EC
ABO blood type was not significantly associated with stage or differentiation of EC in both the univariate and multivariate logistic regression models (Supplemental Tables 2 and 3).However, in the multivariate logistic regression model, we found that postmenopausal patients had a lower risk of advanced-stage EC (OR, 0.22; 95% CI, 0.01-0.33),and hypertension was a risk factor for low differentiation of type I EC (OR, 2.93; 95% CI, 1.18-7.58)(Supplemental Tables 2 and 3).

Discussion
This single-centre, retrospective study showed that type O was the most prevalent ABO blood type among patients with type I EC.Type O blood was associated with a 66% increased risk of type I EC (OR, 1.66).However, ABO blood type was not associated with stage or differentiation of type I EC.
The association between ABO blood type and the occurrence and progression of various malignancies has been reported extensively (Huang et al. 2017, Bothou et al. 2019, Mao et al. 2019, Song et al. 2019).However, few studies have examined the association between ABO blood type and the risk of type I EC.In addition, previous studies mainly focussed on the incidence of type I EC, and did not assess the relationship between ABO blood type and the stage or differentiation of tumours.One study showed that, compared with blood type O, the positive association of blood type A with EC risk was observed even after adjusting for menopausal status, BMI, oral contraceptive use, family history of cancer and other potential confounders (Xu et al. 2011).This study is inconsistent with the present results, which may be due to the use of different methods to confirm ABO blood type (self-reported vs laboratory testing which is more accurate) and differences in population characteristics or study sample size.Regional differences within China may also bring different results.Another study concluded that non-O blood groups have an increased risk of ovarian cancer, whereas no statistically significant differences were observed in patients with cervical cancer and EC (Yuzhalin and Kutikhin 2012).Similarly, a study showed that ABO blood type does not increase either the risk of recurrence or the risk of a dedifferentiated type of EC (Gitas et al. 2020).However, Abu-Zaid et al. (2017) reported that the blood type O was the most prevalent ABO blood type among Saudi Arabian patients with EC, which was consistent with our study.Nakashidze et al. (2014) also reported that the blood type O was the most frequent and was associated with a higher risk of EC in case of menopausal and postmenopausal women.In addition, many studies have also reported the positive association between blood type O and other tumours (Weisbrod et al. 2012(Weisbrod et al. , 2013)).
Although the mechanisms underlying the association between ABO blood type and cancer are not well documented, several possible mechanisms have been proposed, including inflammation, immune surveillance of malignant cells, intercellular adhesion, and membrane signalling (Wolpin et al. 2009, Zhou et al. 2015).The expression of ABO blood type antigens in cancer cells is modified by hypermethylation of the ABO gene promoter, which may be related to the invasion and metastasis of tumours (Zhou et al. 2015).Many previous studies suggested that ABO blood type is related to immune surveillance, intercellular cell adhesion molecule-1, tumour necrosis factor-alpha and E-selectin (Par� e et al. 2008, Zhang et al. 2016).These cytokines are related to cell adhesion and apoptosis, which further supports that the immune response is a bridge between blood type and cancer.In addition, tumour immune escape and linkage disequilibrium between the ABO gene and other genes may also underlie malignant tumours (Gates et al. 2011).
ABH and Lewis antigens were initially discovered on red cells, and subsequent studies found that those antigens were also expressed in other cells, including endometrial epithelial cells (Ravn et al. 1993).EC patients with blood type O, who do not have the A and B genes to encode  glycosyltransferase, express a fucosylated variant (Ley) of the precursor structure (Dabelsteen 2002).The loss of A and B antigens increases cellular motility, and the presence of H epitopes increases resistance to apoptosis (Le Pendu et al. 2001).Moreover, the Ley antigen has procoagulant and angiogenic activities (Le Pendu et al. 2001), which may promote tumour formation.Several studies have also reported that loss of A and B antigens was correlated with the incidence and prognosis in EC and other tumours (Gao et al. 2004, Hakomori 1999).Increasing evidence supports that hotspot mutations in genes, such as POLE, p53, PTEN, CTNNB1, PIK3CA, ARID1A, KRAS, b-catenin, L1CAM, ER, and PR, play an important role in the occurrence and prognosis of EC (Kandoth et al. 2013).Besides, a meta-analysis revealed a significant association between rs505922 C > T polymorphism on the ABO gene and cancer risk (Duan et al. 2015).Whether ABO gene polymorphisms, mutations or changes of ABO blood type antigens are associated with the occurrence of EC remains to be verified in large well-designed studies in the future.
The present results indicate that there is no association of ABO blood type with stage and differentiation of type I EC.This finding of our study is contrary to that of a study from Italy, which showed that patients with the A genotype have a lower risk of G3 type I EC (Mandato et al. 2017).This discrepancy may result from differences in the characteristics of the study populations, sample size or study design.The stage and differentiation of tumours are affected by many factors related to gene mutations, changes in the immune microenvironment, molecular signalling and different therapies (Enane et al. 2018).There are few studies on the association between ABO blood type and stage or differentiation of type I EC.The above single-centre, small sample study and the present study are the only ones examining this association.Thus, multi-centre, large-sample clinical research and rigorously designed basic research are needed.
In this study, we additionally found that patients undergoing menopause had a lower risk of advanced-stage EC.On the one hand, menopausal patients have low levels of oestrogen, and the endometrium is thus not easily affected by this hormone.On the other hand, these patients may have obvious clinical symptoms at an early stage and are more likely to undergo endometrial biopsy than premenopausal patients.We also found that hypertension was a risk factor for poorly differentiated (G3) type I EC.The exact mechanism underlying this effect remains unclear.Hamet (Hamet 1997) suggested that hypertension may increase cancer risk by blocking and subsequently modifying apoptosis, thereby affecting the regulation of cell turnover.Hypertension also related to insulin resistance and hence to insulin-like growth factor 1, which is involved in cell growth and neoplastic progression (Soler et al. 1999).Rodriguez et al. (2021) also reported that patients with hypertension have increased odds of endometrial hyperplasia symptoms.In addition, several literatures reported that hypertension was associated with an increased risk of EC (Weiderpass et al. 2000, Dana et al. 2020).By contrast, hypertension is the most common cardiovascular event among EC patients treated with vascular endothelial growth factor (VEGF) signalling pathway inhibitors, such as bevacizumab, brivanib and dovitinib (Konecny et al. 2015, Rubinstein et al. 2021).The causal relationship between hypertension and EC warrant further study.
Accumulating evidence (Benati et al. 2020, Casarin et al. 2020) suggested that the potential use of novel biomarkers for early diagnosis, management, and predicting the prognosis of EC patients, such as telomere length or presence of glandular cells.In addition, recent data support the feasibility of sentinel lymph node identification in case of EC, especially for early-stage disease, and stress the necessity of an appropriate pre-operative mapping (Casarin et al. 2020, Sozzi et al. 2020, Restaino et al. 2022).Early identification of predictive factors related to disease diagnosis or prognosis will help guide clinical practice.In the future, ABO blood type may be a marker of type I EC susceptibility.
One major strength is the availability of complete clinical and pathological data of patients, and these are reliable data from the real world.Another key advantage is that we not only focussed on the association between ABO blood type and the occurrence of type I EC, but also the stage and differentiation of type I EC.To the best of our knowledge, this is the first time to investigate the association between ABO blood type and the stage or differentiation of type I EC in developing country.In addition, this study included the strict study design and consideration of many confounding factors.However, this study has several limitations.First, this is a retrospective study, and the level of evidence may differ from that of prospective cohort studies.Second, this is a single-centre study that included a limited number of patients, which may result in population selection bias and may not be representative of all populations.We should realise that the rare blood types with cancer could have been referred to specific centres to facilitate and find blood products easily.Third, this was an association study and does not imply causation.Fourth, potential unrecognised confounders may exist, which is common in observational research.Further research are needed to investigate the association of ABO blood type with recurrence of tumour or long-term survival of patients.

Conclusion
In summary, we demonstrated that blood type O was the most prevalent ABO blood type among patients with type I EC and was associated with increased risk of type I EC.There was no significant association between ABO blood type and stage or differentiation of type I EC.However, patients undergoing menopause had a lower risk of advanced-stage type I EC, and hypertension was a risk factor for poorly differentiated type I EC.

Figure 2 .
Figure 2. Distribution of ABO blood type stratified by endometrial cancer and healthy controls.

Figure 3 .
Figure 3. Distribution of ABO blood type in patients with type I endometrial cancer stratified by age, BMI, stage and differentiation.

Table 1 .
Baseline characteristics of patients with type I endometrial cancer stratified by ABO blood type.
BMI: body mass index; PLT: Platelets; Any invasion, including invasion of cervix, lower uterus, vessel, lymph nodes, nerve and left or right side of uterus; FIGO:International Federation of Gynaecology and Obstetrics.SD: standard deviation; IQR: inter quartile range.

Table 2 .
Logistic regression model for the association between ABO blood type and type I endometrial cancer.