**Core Concept**
Paraneoplastic cerebellar ataxia (PCA) is a rare and severe neurological disorder characterized by progressive cerebellar degeneration, often associated with various types of cancer. The presence of specific autoantibodies, such as anti-Yo, helps identify the underlying cause and guides treatment.

**Why the Correct Answer is Right**
Anti-Yo antibodies are a type of onconeural antibody, which are directed against proteins expressed by neurons. In the case of anti-Yo antibodies, they target the cerebellar Purkinje cells, leading to cell death and ataxia. This antibody is commonly found in patients with breast and ovarian cancer, particularly in those with poorly differentiated tumors. The presence of anti-Yo antibodies in PCA patients suggests a paraneoplastic origin, indicating that the immune response is triggered by the tumor.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because anti-Hu antibodies are associated with small cell lung cancer, which typically presents with a different clinical syndrome, such as encephalitis or myelopathy.
**Option B:** This option is incorrect because anti-Ri antibodies are linked to breast and lung cancer, but they are more commonly associated with opsoclonus-myoclonus syndrome.
**Option C:** This option is incorrect because anti-Tr antibodies are associated with paraneoplastic cerebellar degeneration, but they are more commonly linked to Hodgkin lymphoma.

**Clinical Pearl / High-Yield Fact**
When encountering a patient with PCA and anti-Yo antibody positivity, it is essential to investigate for the presence of underlying cancer, particularly breast and ovarian cancer, and to initiate appropriate treatment, including immunotherapy and tumor removal.

**Correct Answer: D. Ovarian cancer**