 c-Fos has also been identified as independent predictor of decreased survival in breast cancer.It was found that overexpression of c-fos from class I MHC promoter in transgenic mice leads to the formation of osteosarcomas due to increased proliferation of osteoblasts whereas ectopic expression of the other Jun and Fos proteins does not induce any malignant tumors.Activation of the c-Fos transgene in mice results in overexpression of cyclin D1, A and E in osteoblasts and chondrocytes, both "in vitro" and "in vivo", which might contribute to the uncontrolled growth leading to tumor.