APC and melanoma: To determine whether β-catenin deficiency in stromal fibroblasts would cause increased melanoma cell death and apoptosis in cocultured spheroids, annexin V-APC and propidium iodide (PI) staining was performed for flow cytometry analysis.29 Because stromal fibroblasts were labeled with GFP, we were able to identify melanoma cells by flow cytometry and calculated the percentage of melanoma cells that were dead or apoptotic.