**4. Risk factors and benefit factors of colorectal cancer in Vietnam**

### **4.1 Performing case-control study on colorectal cancers**

A case-control study was performed for colorectal cancers admitted to Hanoi Cancer Hospital, Viet Duc Surgery Hospital, and Bach Mai General Hospital located in Hanoi. The ratio of case-control is 1:1 with the standards for matching are gender and age (±5). Cases and controls were interviewed to collect data in using demographic and lifestyle questionnaire and semiquantitative food frequency questionnaire. Blood samples were collected in the early morning on the day of operation [23, 24]. Most patients came from the provinces near Hanoi within the Red Delta River. They will be represented as Vietnamese in the north.

### **4.2 Host factors related to colorectal cancer**

### *4.2.1 Blood ABO group and risk of colorectal cancer*

Distribution of blood ABO group in Vietnamese is 45.00, 21.20, 28.30, and 5.50% for types O, A, B, and AB, respectively [49]. In our study, the distribution is different, with 42.97, 23.67, 27.95, and 5.42% for types O, A, B, and AB, respectively [50]. The proportion of type A plus AB is 26.70% while type O plus B is 73.30% in Vietnamese. However, in our study, it is 29.10% and 70.90%, respectively. Distribution of blood ABO group in our study population is similar to that in Vietnamese. Blood ABO group was observed to be associated with cancer risk, whereas blood A was seen to increase the risk of stomach cancer in many studies [51]. Blood A, AB, and B have also increased the risk of pancreatic cancer [52].

In our study, blood type A plus AB was seen to increase the risk of colorectal cancer, with OR = 1.58, 95% CI = 1.05–2.38 [50] (**Table 6**). The mechanism of developing colorectal cancer in patients with blood types A and AB is unknown.

When we separated colon and rectal cancer, the estimated risk was significantly increased for colon cancer, with OR = 3.36, 95% CI = 1.91–5.92, but not significantly increased for rectal cancer, with OR = 0.84, 95% CI = 0.54–1.32.

### *4.2.2 CYP1A1 genotypes risk of colorectal cancer*

The function of CYP1A1 is recognized to be a major chemical carcinogeninduced cancer, in general, and colorectal cancer, in particular, in humans. We found that CYP1A1 (A/G and G/G genotypes) increased the risk of colorectal cancer, with OR = 1.86, 95% CI = 1.16–2.98 (**Table 7**) [50].

### *4.2.3 Family and personal history of health and risk of colorectal cancer*

When parents and close relatives suffered from cancer, the patients are at a higher risk of colorectal cancer, with OR = 3.00, 95% CI = 1.29–6.99, and OR = 3.63,


**Table 6.**

*Blood ABO group and risk of colorectal cancer.*


### **Table 7.**

*CYP1A1 genotypes and the risk of colorectal cancer.*

95% CI = 1.31–10.01, respectively. Patients with a past history of colorectal pain and inflammation are also at a higher risk of cancer, with OR = 3.68, 95% CI = 2.01–6.75. Regarding body mass index (BMI), three levels were categorized, including <18.5; 18.5- < 25, and 25- < 30. Patients with body mass index of 25- < 30 are also at a higher risk of cancer, with OR = 2.09, 95% CI = 0.79–5.51, and *p* for trend <0.05 (**Table 8**) [50]. The Vietnamese households traditionally follow the multigenerational pattern and, therefore, members share living environments as well as similar dietary habits. As a result, all family members might be exposed to the risk of cancer, in general, and the risk of colorectal cancer, in particular. Regarding the body mass index, the mechanism of developing colorectal cancer among the group of obesity was unknown.
