**Core Concept**
Gastric cancer is a malignancy of the stomach that has been associated with various risk factors, including genetic predisposition, dietary habits, and environmental factors. The relationship between blood groups and gastric cancer has been studied extensively, with some studies suggesting a link between certain blood groups and an increased risk of developing gastric cancer.

**Why the Correct Answer is Right**
The correct answer is linked to the ABO blood group system, specifically the A blood group. Studies have consistently shown that individuals with blood group A have a higher risk of developing gastric cancer compared to those with other blood groups. This association is thought to be due to the higher prevalence of Helicobacter pylori infection in individuals with blood group A, which is a known risk factor for gastric cancer.

**Why Each Wrong Option is Incorrect**
**Option B:** Individuals with blood group O have been shown to have a lower risk of gastric cancer, not a higher risk.
**Option C:** There is no established link between blood group B and gastric cancer.
**Option D:** Blood group AB is not associated with an increased risk of gastric cancer.

**Clinical Pearl / High-Yield Fact**
Individuals with blood group A should be aware of their increased risk of gastric cancer and maintain regular screening and surveillance to detect any potential malignancies early.

**Correct Answer: C. Blood group A.**