AIMS: Thermal ablation can evoke an immune response, which may have effects on 
the prognosis of patients with hepatocellular carcinoma (HCC). Our aim is to 
investigate the changes of circulating T-cell subsets after microwave ablation 
(MWA) and to explore the risk factors of tumor recurrence in patients with 
hepatitis B virus (HBV)-related HCC.
METHODS: Thirty patients with HBV-related HCC were enrolled in this study. The 
blood samples were collected both before and after MWA (24 h, 72 h, and 1 month 
after MWA). The distributions of Th17 cells, regulatory Treg-cells, CD4+ 
T-cells, CD8+ T-cells, and CD3+ T-cells were determined by flow cytometer. The 
potential-related factors of tumor recurrence were analyzed by logistic 
regression.
RESULTS: The levels of circulating T-cell subsets, except for Th17 cells, were 
relatively stable after MWA. The frequency of Th17 cells increased from 3.98% ± 
2.40% before treatment to 5.53% ±3.27% 24 h after treatment. Eight of 30 
patients had a tumor recurrence. The results of logistic regression suggested 
that among 11 candidates, only the level of Th17 cells was the risk factor of 
tumor recurrence. To remove the interference from other factors, seven patients 
with tumor(s) >3 cm or alpha-fetoprotein >400 ng/mL were excluded in another 
parallel logistic regression. The results of such regression clearly 
demonstrated that circulating Th17 cells is indeed a related factor of tumor 
recurrence.
CONCLUSIONS: Thermal ablation may evoke a transitional immune response by 
increasing the frequency of Th17 cells. Patients with high levels of baseline 
circulating Th17 cells, instead of the transient elevation of Th17 cells induced 
by MWA, are at the risk of tumor recurrence.