**Core Concept**
Early gastric cancer refers to a type of gastric cancer where the tumor is limited to the mucosa or submucosa, without lymph node metastasis. This distinction is crucial in determining the prognosis and treatment approach for gastric cancer patients.

**Why the Correct Answer is Right**
The correct answer is related to the definition and classification of gastric cancer. Gastric cancer is typically staged based on the depth of tumor invasion and the presence of lymph node metastasis. Early gastric cancer is diagnosed when the tumor is confined to the mucosa or submucosa, with no lymph node involvement. This is often associated with a better prognosis compared to more advanced stages of gastric cancer.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the characteristics of early gastric cancer. While tumor size can be an important factor in staging, it is not the defining feature of early gastric cancer.

**Option B:** This option is incorrect because it implies that early gastric cancer is characterized by the presence of lymph node metastasis, which is actually a feature of more advanced stages of gastric cancer.

**Option C:** This option is incorrect because it suggests that early gastric cancer is always associated with a good prognosis, which is not necessarily true. While early gastric cancer has a better prognosis compared to more advanced stages, individual patient outcomes can vary depending on various factors.

**Clinical Pearl / High-Yield Fact**
It is essential for clinicians to accurately diagnose and stage gastric cancer to determine the most appropriate treatment approach. Early gastric cancer may be treated with endoscopic resection or surgery, whereas more advanced stages may require more aggressive treatments such as chemotherapy or radiation therapy.

**Correct Answer:** A.