We postulate that (i) fibroblasts in contact with breast cells have higher aromatase activity, thereby enhancing estrogen biosynthesis, which in turn favors the progression of breast cancer [15], and (ii) although aromatase expression in breast cancer cells was not increased in our model, other markers that are able to stimulate aromatase activity, such as IL6, TNFα, IGF-1, exhibited greater mRNA expression [32]. The gene discussed is TNF; the disease is breast cancer.