**Core Concept**
Gestational trophoblastic neoplasia (GTN) is a group of rare, malignant tumors that develop in the uterus during pregnancy. GTN can be classified into several types, including invasive mole, choriocarcinoma, placental-site trophoblastic tumor, and epithelioid trophoblastic tumor. The FIGO (International Federation of Gynecology and Obstetrics) staging system is used to classify GTN based on the extent of spread.

**Why the Correct Answer is Right**
The correct staging of GTN with lung metastasis is FIGO Stage IV. This is because lung metastasis indicates distant spread of the disease, which is a significant prognostic factor. The FIGO staging system takes into account the presence of metastasis, the number of metastatic sites, and the extent of tumor involvement in the lungs. In this case, the presence of lung metastasis is a key factor in determining the stage of the disease.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the staging of GTN.
**Option B:** This option may be relevant to the staging of other cancers, but not GTN.
**Option C:** This option is incorrect because GTN with lung metastasis is classified as Stage IV, not Stage III.

**Clinical Pearl / High-Yield Fact**
When staging GTN, it is essential to consider the presence of distant metastasis, such as lung or brain metastasis, which significantly impacts prognosis and treatment.

**Correct Answer:** C.