While biomarker-guided treatments and NGS-based approaches are refining precision medicine, they are not universally applicable. The gap between the genomic characterization of tumors and their functional behavior is becoming increasingly evident. There is an escalating demand for functional assays that can customize cancer treatments for individual patients and bridge this gap. We have developed OncoFlow, an integrated microfluidic platform that automates viability assays. This platform customizes treatment options by assessing the functional responses of a patient's tumor cells to a specific drug panel. This study specifically addressed non-small cell lung adenocarcinoma (NSCLC) in patients presenting pleural effusion. We used the NCI-H2228 adenocarcinoma cell line, which harbors the EML4-ALK fusion oncogene, to develop and fine-tune the viability assay. Cells cultivated in microfluidic chambers were treated with various concentrations of the tyrosine kinase inhibitors alectinib and crizotinib, and the cytotoxic effects were measured. The results were consistent with those from conventional cell culture methods, thereby validating the assay's reliability. Next, pleural effusion samples from six NSCLC patients, four of them harboring the EML4-ALK rearrangement were tested with alectinib and crizotinib using the OncoFlow system. Monitoring and analysis of cell viability showed varied sensitivities to crizotinib, while all samples exhibited resistance to alectinib. These findings underscore OncoFlow's potential to enhance physician decision-making and customize treatment plans, ultimately improving patient outcomes.