A total of 165 patients with sCRLM who met the inclusion criteria were included in this study. After pre-ablative chemotherapy, 68 patients had at least one DLM and 97 showed no DLM. Of 165 patients, 32 (19.4%) underwent a liver-first approach, 69 (41.8%) a concurrent approach and 64 (38.8%) a bowel-first approach. The patient demographics of patients with and without DLM were summarized in Table 1. The median follow-up period was 48.2 months (95% CI: 41.9–54.5 months). The median age in patients with and without DLM were 60 (53, 65) and 58 (52, 64), respectively. Patients with more than two sCRLM at the time of diagnosis and more than two sCRLM at the time of MWA were found more prevalent in patients with DLM than those without DLM (p < 0.001 and p = 0.010, respectively). No significant differences were observed in other factors between the two groups (all p > 0.050).

The characteristics of pre-ablative chemotherapy were listed in Table 2. Patients with DLM underwent more cycles of pre-ablative chemotherapy than those without DLM (median cycles: 6 (4, 8) vs. 4 (3, 6), p < 0.001). There were no significant differences regarding the pre-ablative chemotherapy regimens used.

The 1:1PSM analysis was also performed between the groups of patients to reduce the impact of bias. Ultimately, 66 patients were assessed and each subgroup included 33patients. The P-values for all covariates were greater than 0.05, indicating that propensity scores for the two groups significantly overlapped (Table 3).

During follow-up, intrahepatic disease progression occurred in 79.4% (54/68) and 45.4% (44/97) of patients with and without DLM, respectively (p < 0.001). The recurrence patterns for patients with and without DLM were shown in Table 4. For patients with DLM, in situ recurrence occurred in 31 patients (including 8 LTP, 23 DLM site recurrences). For patients without DLM, in situ recurrence occurred in 13 patients who developed LTP. The in situ recurrence rate was significantly higher for patients with DLM than those without DLM (45.6% (31/68) versus 13.4% (13/97), p < 0.001). There was no statistical difference of de novo recurrence between two groups (33.8% (23/68) versus 31.9% (31/97), p = 0.802).

Before PSM, the 1-year, 3-year, and 5-year ihPFS rates for patients with DLM were 55.7%, 36.8%, and 30.6%, respectively, which is significantly lower than patients without DLM whose 1-year, 3-year, and 5-year ihPFS were 70.8%, 59.3%, and 52.0%, respectively. (p-value = 0.012, Fig. 1). After PSM, the ihPFS rates for patients with DLM were 44.9%, 31.8%, and 21.2% at 1-year, 3-year, and 5-year, respectively, which is significantly lower than patients without DLM whose 1-year, 3-year, and 5-year ihPFS were 72.3%, 58.8%, and 47.5%, respectively. (p-value = 0.039, Fig. 2).

ihPFS of patients with and without DLM before propensity score matching

ihPFS of patients with and without DLM after propensity score matching

On univariable cox regression, extrahepatic metastasis (HR: 1.7; 95% CI: 1.1–2.6; p = 0.029), ablated tumor number (HR: 1.6; 95% CI: 1.0–2.5.0.5; p = 0.036), and DLM (HR: 1.7; 95% CI: 1.1–2.7; p = 0.013) were identified as three independent factors associated with poor ihPFS. On multivariable analyses, extrahepatic metastasis (HR: 1.8; 95% CI: 1.1–2.8; p = 0.018), T4 stage primary cancer (HR: 1.8; 95% CI: 1.0–3.0; p = 0.043), tumor size > 16 mm (HR: 1.9; 95% CI: 1.2–3.0.2.0; p = 0.007), and DLM (HR: 2.2; 95% CI: 1.1–4.1; p = 0.009) were identified as risk factors associated with ihPFS (Table 5).

Before PSM, the difference of OS was not statistically significant between patients without and with DLM (100% vs. 97.0%, 72.5% vs. 63.3%, and 61.8% vs. 45.2% for 1-year, 3-year and 5-year OS, respectively, p-value = 0.11, Fig. 3). After PSM, the difference of OS was still not statistically significant between patients without and with DLM (100% vs. 93.8%, 53.9% vs. 61.1%, and 53.9% vs. 38.2% for 1-year, 3-year and 5-year OS, respectively, p-value = 0.49, Fig. 4).

OS of patients with and without DLM before propensity score matching

OS of patients with and without DLM after propensity score matching

On univariable cox regression, age over 60 (HR: 2.0; 95% CI: 1.2–3.3; p = 0.009) and right colon cancer (HR: 2.5; 95% CI: 1.3–5.0.3.0; p = 0.008) were identified as independent factors associated with poor OS. On multivariable analyses, age over 60 (HR: 2.3; 95% CI: 1.4–4.0.4.0; p = 0.002), right colon cancer (HR: 2.5; 95% CI: 1.2–5.2; p = 0.011) were identified as risk factors associated with OS (Table 6).