CCNA2 and breast cancer: Moreover, because multiple studies have suggested that the oncogenic effects of cyclins may not be simply due to enhanced tumor cell growth or proliferation but may also involve tumor promoting functions [45-48], we examined the effect of TGFβ on protein expression levels of cyclins A, B1, D1 and D2 in the human aggressive breast cancer cell lines MDA and its metastatic sub-progeny SCP2 [49].