**Core Concept**
In ovarian cancer, lymph node involvement is a critical factor in staging. The FIGO (International Federation of Gynecology and Obstetrics) staging system for ovarian cancer categorizes the disease based on the extent of spread, including lymph node involvement.

**Why the Correct Answer is Right**
Inguinal lymph nodes are involved in ovarian cancer when the disease has spread beyond the pelvis and abdominal cavity, specifically to the lower limbs. This occurs in Stage IVb, which is characterized by distant metastasis, including to the inguinal lymph nodes. The involvement of inguinal lymph nodes indicates a more advanced stage of the disease, with a poorer prognosis.

**Why Each Wrong Option is Incorrect**
**Option A:** Stage II ovarian cancer is characterized by involvement of the pelvic or retroperitoneal lymph nodes, not inguinal lymph nodes.

**Option B:** Stage IIIa ovarian cancer involves the peritoneal surfaces and/or regional lymph nodes, but not inguinal lymph nodes.

**Option C:** Stage IIIc ovarian cancer involves distant metastasis, but not specifically to the inguinal lymph nodes.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that ovarian cancer staging is crucial for determining treatment options and predicting prognosis. Inguinal lymph node involvement is a red flag for distant metastasis and requires a more aggressive treatment approach.

**✓ Correct Answer: D. Stage IVb. Ovarian cancer spreads to inguinal lymph nodes in Stage IVb.**