Purpose To determine whether variable hepatic microwave ablation (MWA) can induce local
inflammation and distant pro-oncogenic effects compared with hepatic
radiofrequency ablation (RFA) in an animal model. Materials and Methods In this institutional Animal Care and Use Committee-approved study, F344 rats (150 gm, n = 96) with subcutaneous R3230 breast
adenocarcinoma tumors had normal non-
tumor-bearing liver treated with RFA (70°C × 5 minutes), rapid higher-power MWA (20 W × 15 seconds), slower lower-power MWA (5 W × 2 minutes), or a
sham procedure (needle placement without energy) and were sacrificed at 6 hours to 7 days (four time points; six animals per arm per time point). Ablation settings produced 11.4 mm ± 0.8 of coagulation for all groups. Distant
tumor growth rates were determined to 7 days
after treatment. Liver
heat shock protein (HSP) 70 levels (at 72 hours) and macrophages (CD68 at 7 days),
tumor proliferative indexes (Ki-67 and CD34 at 7 days), and serum and tissue levels of
interleukin 6 (IL-6) at 6 hours,
hepatocyte growth factor (HGF) at 72 hours, and
vascular endothelial growth factor (
VEGF) at 72 hours after ablation were assessed. All data were expressed as means ± standard deviations and were compared by using two-tailed t tests and analysis of variance for selected group comparisons. Linear regression analysis of
tumor growth curves was used to determine pre- and posttreatment growth curves on a per-
tumor basis. Results At 7 days, hepatic ablations with 5-W MWA and RFA increased distant
tumor size compared with 20-W MWA and the
sham procedure (5-W MWA: 16.3 mm ± 1.1 and RFA: 16.3 mm ± 0.9 vs
sham: 13.6 mm ± 1.3, P < .01, and 20-W MWA: 14.6 mm ± 0.9, P < .05). RFA and 5-W MWA increased postablation
tumor growth rates compared with the 20-W MWA and
sham arms (preablation growth rates range for all arms: 0.60-0.64 mm/d; postablation: RFA: 0.91 mm/d ± 0.11, 5-W MWA: 0.91 mm/d ± 0.14, P < .01 vs pretreatment; 20-W MWA: 0.69 mm/d ± 0.07,
sham: 0.56 mm/d ± 1.15; P = .48 and .65, respectively).
Tumor proliferation (Ki-67 percentage) was increased for 5-W MWA (82% ± 5) and RFA (79% ± 5), followed by 20-W MWA (65% ± 2), compared with
sham (49% ± 5, P < .01). Likewise, distant
tumor microvascular density was greater for 5-W MWA and RFA (P < .01 vs 20-W MWA and
sham). Lower-energy MWA and RFA also resulted in increased HSP 70 expression and macrophages in the periablational rim (P < .05). Last,
IL-6, HGF, and
VEGF elevations were seen in 5-W MWA and RFA compared with 20-W MWA and
sham (P < .05). Conclusion Although hepatic MWA can incite periablational
inflammation and increased distant
tumor growth similar to RFA in an animal
tumor model, higher-power, faster heating protocols may potentially mitigate such undesired effects. © RSNA, 2016.