Application of Tumor Burden Score for predicting conversion outcome in patients with initially unresectable colorectal liver metastases after first-line systemic therapy

BACKGROUND: Patients with initially unresectable colorectal liver metastases (CRLM) could achieve survival benefit from successful conversion therapy. Recently, Tumor Burden Score (TBS) was proposed as a valuable index to predict outcome following resection of CRLM. The study is aimed to investigate the association of TBS with conversion outcome. METHODS: A total of 234 patients who underwent first-line treatment in our center were enrolled as training cohort. The validation cohort was developed from 89 patients in our previous study. Cut-off value of TBS was calculated to stratify patients into two groups. Significance test and logistic regression model were used to examine the prediction value of TBS for conversion outcome after first-line systemic therapy. Kaplan–Meier method and Cox proportional hazard model were applied to assess the prognostic value of TBS. RESULTS: TBS showed good discriminatory power [area under curve (AUC) 0.726, p < 0.001] with cut-off value defined as 14.3 in training cohort, which was validated in the validation cohort. Increasing TBS was related to adverse chemotherapy response and conversion outcome. Low TBS group had three times higher conversion rate than that in high TBS group (57.3% versus 19.0%, p < 0.001). Multivariate analysis indicated that high TBS [odds ratio (OR) = 3.676, 95% confidence interval (CI) 1.671–8.429, p = 0.002], first-line treatment response as stable disease (SD) or progressive disease (PD) (OR = 9.247; 95% CI 4.736–18.846, p < 0.001), and absence of targeted therapy (OR = 2.453, 95% CI 1.139–5.455, p = 0.024) were three independent risk factors for failure conversion outcome. High TBS was significantly associated with conversion outcome whatever chemotherapy response, addition of targeted therapy, and Kirsten rat sarcoma viral oncogene homolog (KRAS) status. High TBS was also associated with worse overall survival. CONCLUSION: TBS should be applied in clinical practice to predict conversion outcome in patients with initially unresectable CRLM.