Is anchorage independence necessary for malignant transformation in mammary epithelial cells?
Clinical data support the idea that independence from BM-directed survival is linked to malignant transformation in the breast. Immunologic studies [20] have shown that invasive breast tumor cells exhibit a reduced level of apoptosis when compared with cells located in benign ductal carcinoma in situ (DCIS) lesions. Similarly, intense staining for focal adhesion kinase, a tyrosine kinase that can induce anchorage-independent survival in epithelial cells, was detected both in invasive tumor cells and in groups of premalignant cells within adjacent DCIS lesions [21]. Unfortunately, these data do not establish whether the enhanced survival in the transformed cells is due to genetic selection or is mediated via microenvironmental factors. Although genetics undoubtedly plays a critical role in driving malignant transformation and apoptosis resistance in the breast, evidence is slowly accumulating that microenvironmental factors must also play a role in these processes. For example, angiogen
