**Core Concept**
Metastasis to the ovary is a relatively rare phenomenon, but certain cancers have a propensity to spread to this site. The ovary's rich vascular supply and the presence of peritoneal surfaces create a potential route for metastatic cells to implant and grow.

**Why the Correct Answer is Right**
Metastasis to the ovary is often seen in cancers of the abdominal or pelvic organs, which drain into the peritoneal cavity. The most common tumours to metastasize to the ovary include gastrointestinal cancers, such as gastric and colorectal cancer. These cancers can spread through the peritoneal fluid, leading to implantation on the ovarian surface.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because breast cancer is not commonly associated with ovarian metastasis. While it is possible for breast cancer to spread to the ovaries, it is not a characteristic feature of this disease.
**Option B:** This option is incorrect because endometrial cancer is not typically known to metastasize to the ovaries. While endometrial cancer can spread to the pelvic lymph nodes, ovarian metastasis is not a common occurrence.
**Option C:** This option is incorrect because ovarian cancer itself is not a good example of a tumour metastasizing to the ovary. While ovarian cancer can spread to other parts of the body, metastasis to the ovary is not a characteristic feature of this disease.

**Clinical Pearl / High-Yield Fact**
When considering metastasis to the ovary, it's essential to remember that the ovary's location and vascular supply make it a potential site for implantation of metastatic cells from abdominal or pelvic cancers.

**Correct Answer:** D.