Employing three-dimensional (3D) in vitro models, including tumor organoids and spheroids, stands pivotal in enhancing cancer therapy. These models bridge the gap between 2D cell cultures and complex in vivo environments, effectively mimicking the intricate cellular interplay and microenvironmental factors found in solid tumors. Consequently, they offer versatile tools for comprehensive studies into cancer progression, drug responses, and tailored therapies. In this study, we present a novel open-surface microfluidic-integrated platform called the Tumoroid-on-a-Plate (ToP) device, designed for generating intricate predictive 3D solid tumor models. By incorporating a tumor mass, stromal cells, and extracellular matrix components, we successfully replicate the complexity of glioblastoma (GBM) and pancreatic adenocarcinoma (PDAC) within our system. Using our advanced ToP model, we were able to successfully screen the effect of various GBM extracellular matrix compositions, such as Collagen and Reelin, on the invasiveness of the GBM cells with the ToP model. The ToP in vitro model also allowed for the screening of chemotherapeutic drugs such as temozolomide and iron-chelators in a single and binary treatment setting on the complex ECM-embedded tumoroids. This helped to investigate the toxic effect of different therapeutics on the viability and apoptosis of our in vitro GBM and PDAC cancer models. Additionally, by co-culturing human-derived fibroblast cells with PDAC tumoroids, the pro-invasive impact of the stromal component of the tumor microenvironment on growth behavior and drug response of the tumoroids was revealed. This study underscores the transformative role of predictive 3D models in deciphering cancer intricacies and highlights the promise of ToP in advancing therapeutic understanding.