Based on the surface expression levels of EpCAM, HER2, FAP and PD-L1, we chose to generate mixed multicellular tumor spheroids by blending the MCF-7 breast cancer cell line and FAP-transfected HT-1080 fibrosarcoma cells serving as a surrogate for FAP-expressing cancer-associated fibroblasts in tumor stroma. Here, ERBB2 is linked to breast carcinoma.