## **Core Concept**
The staging of ovarian cancer is primarily based on the International Federation of Gynecology and Obstetrics (FIGO) staging system, which classifies the extent of spread of the tumor. The staging is crucial for determining prognosis and treatment.

## **Why the Correct Answer is Right**
In this scenario, the patient has a unilateral ovarian tumor with ascites that is positive for malignant cells. The presence of malignant cells in the ascites indicates that the cancer has spread beyond the ovaries, but all other structures were found to be free of disease during laparotomy. According to the FIGO staging system, the presence of malignant cells in ascites or peritoneal washings is classified as Stage IC.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Stage IA refers to a tumor that is limited to one ovary with intact capsule and no tumor on ovarian surface and no malignant cells in ascites or peritoneal washings. This does not match the given scenario because the ascites is positive for malignant cells.
- **Option B:** Stage IB refers to a tumor limited to both ovaries with intact capsules and no tumor on ovarian surface and no malignant cells in ascites or peritoneal washings. This option is incorrect because it involves both ovaries and does not account for the malignant cells in ascites.
- **Option D:** Stage II involves the tumor involving one or both ovaries with pelvic extension. This option does not match because the scenario explicitly states that all other structures were free of disease.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the FIGO staging system for ovarian cancer is surgically based, and the presence of malignant cells in ascites or peritoneal washings directly impacts staging, specifically moving it to Stage IC.

## **Correct Answer:** . Stage IC.