Prognostic factors for thermo-ablation of liver metastases in colon cancer: A Maltese perspective.

267 Background: Malta is a small Mediterranean archipelago with an annual colon cancer incidence of 300 patients per year and a cumulative 5-year overall survival of 58%. Despite major improvements in therapeutic strategies, colon cancer remains the third leading cause of cancer deaths locally with an annual mortality rate of circa 110 patients per year. Percutaneous thermal ablation of colorectal liver metastases involves exposure of metastatic deposits to temperature extremes using radiofrequency, microwave or cryotherapy. The role of this case series was to examine the prognostic value of clinico-pathological variables to provide insight into patient selection for ablative therapy. Methods: This retrospective analysis of 66 adult patients with colorectal liver oligometastatic disease who underwent thermal ablation between January 2014 and January 2022, reviews demographic and pathological criteria including tumour grade, presence of vascular invasion, mismatch repair and k-RAS & BRAF mutational status, CEA & Ca19.9 assay at time of treatment. Other parameters include metachronous versus synchronous disease, hepatic burden and concurrent chemotherapy. All these co-variables were analysed using the Cox Regression Hazard model to assess their impact on progression free- (PFS) and overall survival (OS). Results: For this patient cohort, the mean PFS and OS were 13.1 and 33.8 months. Our data indicates that most individuals experience progression within the first 10 months, with a gradual decline in PFS for the remaining individuals. A Ca19.9 level within normal limits (p=0.004, HR 0.157-0.700 95% CI) was related to an improved PFS but not OS. The presence of synchronous metastases (p=0.004, HR 0.168-0.715 95% CI) and ablation of one lesion (p=0.013 HR 0.191 (0.052-0.702 95 CI) were favourable prognostic markers for improved OS. k-RAS wt status was a prognostic adverse biomarker for PFS (p=0.002, HR 1.529, 6.686 95% CI). There was a paucity of data for BRAF and MMR status so these were excluded from the final analysis. No statistical survival benefit was noted for patients treated with chemotherapy, and other variables including gender, age, primary tumour sidedness, LVSI or CEA value. Conclusions: There are two surprising trends here- the paucity of survival benefit for the use of chemotherapy in conjunction with ablation and the worse outcome for k-ras wt tumours. We postulate that the absence of BRAF sub-stratification at the time of patient accrual, impacted statistical hazard. This case series suggests that the prognosis and survival of colorectal liver oligometastatic disease is multifactorial and complex, highlighting the need for further genomic and molecular insights.