A Mathematical Model to Estimate Chemotherapy Concentration at the Tumor-Site and Predict Therapy Response in Colorectal Cancer Patients with Liver Metastases

Chemotherapy remains a primary treatment for metastatic cancer, with tumor response to chemotherapy being the benchmark outcome marker. However, therapeutic response in cancer is unpredictable due to significant heterogeneity in drug delivery from systemic circulation to solid tumors, which also remains remarkably understudied. In this proof of concept study, we evaluated chemotherapy concentration at the tumor-site and its association with therapy response by applying a mathematical model of tumor perfusion. Using pre-chemotherapy imaging, clinical and biologic variables, and chemotherapy regimen to inform the model, we estimated tumor-site chemotherapy concentration in patients with colorectal cancer liver metastases, who received chemotherapy prior to surgical hepatic resection with curative-intent. The differential response to therapy in resected specimens, measured with the gold-standard tumor regression grade (TRG; from 1, complete response to 5, no response), was examined relative to the model predicted systemic and tumor-site chemotherapy concentrations. We found t hat average calculated plasma concentration of the cytotoxic drug was essentially equivalent across patients exhibiting different TRGs, while the estimated tumor-site chemotherapeutic concentration (eTSCC) showed a quadratic decline from TRG=1 to TRG=5 ( P < 0.001). The eTSCC was significantly lower than the observed plasma concentration and dropped by a factor of ~5 between patients with complete response (TRG=1) and those with no response (TRG=5), while the plasma concentration remained stable across TRG groups. TRG variations were driven and predicted by differences in tumor perfusion and eTSCC. These findings represent the groundwork that may form the basis of a paradigm shift in the care of potentially curable colorectal cancer with liver metastases and other hypovascular tumors. Notably, this approach can be extended beyond chemotherapy, to therapies where drug concentration at the tumor site is the limiting factor of treatment efficacy, including immunotherapy.