**Core Concept**
A Sister Mary Joseph nodule refers to the presence of a palpable nodule bulging into the umbilicus, often indicating metastasis from an intra-abdominal malignancy. This clinical sign is associated with various cancers, particularly those originating in the abdominal cavity.

**Why the Correct Answer is Right**
The Sister Mary Joseph nodule is most commonly seen in gastric cancer. This is due to the direct spread of cancer cells from the stomach to the umbilicus through the peritoneal cavity. The peritoneum is a thin layer of tissue that lines the abdominal cavity and covers most of the abdominal organs. Cancer cells can easily invade this layer and spread to other parts of the abdomen, including the umbilicus.

**Why Each Wrong Option is Incorrect**
**Option A:** Ovarian cancer can cause ascites and umbilical metastases, but it is not the most common cause of Sister Mary Joseph nodule.
**Option B:** Colorectal cancer can also metastasize to the peritoneum, but it is less frequently associated with Sister Mary Joseph nodule compared to gastric cancer.
**Option D:** Hepatic cancer can cause umbilical metastases, but it is not the most common cause of Sister Mary Joseph nodule.

**Clinical Pearl / High-Yield Fact**
Sister Mary Joseph nodule is a classic example of a paraneoplastic syndrome, where a malignancy causes a distant clinical manifestation that is not directly related to the primary tumor site.

**Correct Answer:** C. Gastric cancer.