The interplay between genes and environment is complex, particularly when it comes to cancer. Studies on breast cancer cells have shown that environmental influences dominate over genotype in their effect on phenotype, and can cause cancerous cells to revert to a non-malignant phenotype, while remaining genotypically malignant. Using breast tissue in three-dimensional cell culture has proved a better model than traditional two-dimensional cell culture in that different cell types can be seen to behave differently to the same pro-apoptotic signal, with normal cells surviving.