A 32-year-old woman presents with vaginal bleeding and lower abdominal pain 6 weeks after a spontaneous abortion. Ultrasound shows heterogeneous intrauterine mass with cystic spaces. hCG is 85,000 mIU/mL. Which feature best distinguishes invasive mole from choriocarcinoma in the context of gestational trophoblastic neoplasia?

Explanation

## Invasive Mole vs. Choriocarcinoma: Pathological Discrimination ### Defining Gestational Trophoblastic Neoplasia (GTN) **Key Point:** The **presence or absence of chorionic villi** is the single most important histological discriminator between invasive mole and choriocarcinoma. The question asks which feature **best distinguishes invasive mole** — and that feature is the **presence of chorionic villi with trophoblastic invasion into the myometrium** (Option C). | Feature | Invasive Mole | Choriocarcinoma | |---------|---------------|------------------| | **Chorionic villi** | **Present** | Absent | | **Trophoblastic invasion** | Into myometrium, rarely beyond | Hematogenous (lungs, brain, liver) | | **Histology** | Molar tissue + myometrial invasion | Pure trophoblastic tissue (cyto + syncytio) | | **Origin** | Usually from complete molar pregnancy (50%) | Can arise from any pregnancy | | **Metastases** | Rare, late | Common, early (40–50% at diagnosis) | | **hCG level** | Elevated but variable | Often very high | | **Prognosis** | Better; often single-agent chemo | Requires aggressive multi-agent chemotherapy | ### Why Option C is Correct **High-Yield:** Invasive mole is defined by **hydropic chorionic villi that invade the myometrium** (and occasionally parametrium or vagina), but extrauterine hematogenous spread is rare. The hallmark distinguishing it from choriocarcinoma is the **retention of villous architecture** despite deep invasion. **Clinical Pearl:** Choriocarcinoma, by contrast, shows **no chorionic villi** on histology — it consists purely of sheets of cytotrophoblasts and syncytiotrophoblasts with extensive hemorrhage and necrosis, and spreads hematogenously to lungs, brain, and liver early in its course. ### Why Option B is Incorrect as the "Best Distinguishing Feature of Invasive Mole" Option B ("absence of chorionic villi with hematogenous spread to lungs and brain") describes **choriocarcinoma**, not invasive mole. The question asks which feature best distinguishes **invasive mole** — so the correct answer must describe the defining feature of invasive mole, not choriocarcinoma. Option C correctly identifies the invasive mole's hallmark: villi present + myometrial invasion + no extrauterine spread. **Mnemonic:** **IM = Invasive Mole = villi present + local (myometrial) invasion**; **CC = Choriocarcinoma = villi absent + hematogenous spread** ### Why Other Options Are Incorrect - **Option A:** Trophoblastic proliferation *limited to endometrium without myometrial involvement* describes a hydatidiform mole, not invasive mole. By definition, invasive mole requires myometrial invasion. - **Option D:** Presence of both cytotrophoblast and syncytiotrophoblast with early vaginal metastases is more characteristic of choriocarcinoma; vaginal metastases are not a defining feature of invasive mole. [cite:Robbins 10e Ch 22 — Gestational Trophoblastic Disease] [cite:Dutta's Textbook of Gynecology 8e — Gestational Trophoblastic Neoplasia]