At Okomera, we have developed a unique technology for miniaturized, automated and functional 3D cell assays in precision cancer medicine. Our droplet microfluidic workflow enables to encapsulate patient cancer cells from a biopsy and quickly form a single microtumor per droplet. These droplets are immobilized on a microarray during the experiment. Thanks to the ability to add and merge several sequential droplets with the initial ones, new content can be added to the microtumors on-demand, leading to the integration of various features. For instance, the microtumors can be submitted to an anti-cancer drug library (up to a 100 different conditions) barcoded with fluorescent dyes. To assess the response to immuno-therapy, the microtumors can be co-cultured with immune cells. To mimic the microenvironment, various hydrogels such as Matrigel™ can be added in the droplets. All chips are compatible with various microscopy technologies, therefore we can use live or end-point fluorescent staining, including immuno-fluorescent staining on chip. To assess the efficacy of two chemotherapies (cisplatin and etoposide) on the Ewing's sarcoma cell line A673, we performed combinatorial screening on chip. Microtumors were formed in 500 nL droplets and fused with secondary droplets containing fluorescent barcoded drugs at different concentrations (49 combinatorial drug concentrations). Differences in microtumor viability were analyzed on around 300 microtumors per experiment. This enabled accurate estimation of IC50 values for each drug, in agreement with measurements obtained in standard ultra-low attachment multiwell plates. Synergies between the two treatments were found when both drugs were tested simultaneously or sequentially. Interestingly, sequential combination treatment with etoposide applied 24 hours before cisplatin resulted in an amplified synergistic effect. We applied this technology to investigate treatment options on luminal B breast cancer. Cancer cells from a Patient-Derived Xenograft (PDX) were encapsulated in 50 nL droplets and treated with a small anti-estrogen drug library for 7 days. 4-OH-Tamoxifen was found to kill the PDX cells at day 8 only, while the Fulvestrant+Everolimus combination showed significant effect after 4 days. As a proof-of-concept, primary ovarian tumor cells from surgery were encapsulated in 50 nL droplets, forming microtumors over 24 hours. At this point, primary CD8+ tumor infiltrating lymphocytes were added at a 10:1 ratio, which resulted in significant cytotoxicity after 24 hours. At Okomera, we provide a laboratory instrument and microfluidic consumables enabling the formation of up to a 1000 microtumors in a single run. By using microfluidic droplets, we critically optimize the patient material use, going down to 50 cells per droplet and still enabling high-throughput multiplexing in relevant microenvironments. Furthermore, we are developing an Artificial Intelligence-powered analysis software to segment the cells, to extract quantitative features from microscopy images of the chips and to assess drug efficacy ex vivo for precision cancer medicine.