Outcomes of ultrasound-guided percutaneous ablation of &gt;5 <i>versus</i> ≤ 5 colorectal liver metastases: a propensity score matching study

To investigate the effectiveness and safety of microwave ablation (MWA) in patients with 1–5 colorectal liver metastases (CRLM) <i>versus</i> those with 6–9 CRLM. Data from patients with 1–9 CRLM, who underwent ultrasound (US)-guided percutaneous MWA between January 2018 and May 2023, were retrospectively analyzed. Propensity score matching (PSM) at a ratio of 1:2 was used to balance potential bias between the groups. Data from 264 patients were included in the analysis. After PSM, there were 43 and 75 patients in the CRLM &gt;5 and ≤5 groups, respectively. Even with higher tumor burden and technical difficulty, there was no statistical difference in the local tumor progression (LTP)-free survival (LTPFS) between the groups (<i>p</i> &gt; 0.05). Patients with an ablation margin (AM) ≤5 mm exhibited a significantly higher rate of LTP than those with AM &gt;5 mm in both groups(<i>p</i> &lt; 0.05). Patients with 6–9 CRLM experienced a higher incidence of intrahepatic recurrence (iHR) (<i>p</i> = 0.041) and shorter progression-free survival (PFS) at any site (<i>p</i> &lt; 0.05). CRLM &gt; 5 is an independent risk factor for poor PFS (<i>p</i> = 0.008). The minor complication rate was lower in the CRLM ≤ 5 group (<i>p</i> &lt; 0.05) and the major complication rate showed no difference (<i>p</i> &gt; 0.05). When the number of CRLM was limited to 9, single-session MWA was feasible and safe for radical local treatment. An AM &gt;5 mm was critical for local tumor control. Compared with patients with 1–5 CRLM, those with 6–9 CRLM experienced inferior PFS at any site, which mainly lies in more iHR.