Persistent Low-Level hCG After Gestational Trophoblastic Neoplasia Remission: Treatment-Free Probability Stratified by Early hCG Course.

Background/Objectives: To determine treatment-free probability after persistent low-level human chorionic gonadotropin (hCG) elevation following complete remission from gestational trophoblastic neoplasia (GTN) and examine its association with the early hCG course. Methods: This single-center retrospective study included patients treated in 2015-2022 for gestational choriocarcinoma or invasive mole who developed ≥3 post-remission hCG results >5 and ≤1000 U/L over ≥14 days. The primary endpoint was retreatment for GTN recurrence. Kaplan-Meier analysis estimated treatment-free probability from the first low-level hCG elevation. Exploratory landmark analyses at 60, 90, and 180 days stratified patients still under observation by pre-landmark peak hCG (≤20 versus >20 U/L). Results: Forty-six patients contributed 595 hCG measurements. Thirty-five developed recurrence requiring retreatment; 11 remained recurrence-free. All patients whose first low-level hCG exceeded 20 U/L (n = 11) developed recurrence. Treatment-free probability was 30.4% at 1 year and 24.2% at 2 years. At the 60-, 90-, and 180-day landmarks, 365-day treatment-free probability was higher with pre-landmark peak hCG ≤ 20 U/L than >20 U/L: 68.4% versus 9.1%, 70.6% versus 22.2%, and 92.3% versus 14.3%, respectively. All 35 retreated patients achieved hCG ≤ 5 U/L after treatment. Conclusions: Most patients with persistent low-level hCG after remission from GTN developed recurrence. For patients still under observation at 60, 90, or 180 days, a peak hCG of 20 U/L or lower before the landmark was associated with higher treatment-free probability over the following year. Continued surveillance after clinical and imaging assessment is reasonable in this subgroup.