Tumor Hypoxia: How Conventional Histology Is Reshaped in Breast Carcinoma.

Intratumoral hypoxia is common in any form of malignancy initializing focal necrosis or tumor cell adaptation. Hypoxia inducible factor-1-driven reprogramming favors the loss of tumor cell proliferation (quiescence) and partial cellular reversion, induces stemness and/or mesenchymal-like features in the exposed tumor areas. The characteristic hypoxia-driven tumor cell phenotype is principally directed to reduce energy consumption and to enhance survival, but the gained features also contribute to growth advantage and induce the reorganization of the microenvironment and protective mechanisms against external stress. The hypoxia-induced phenotypic changes are at least in part reflected by conventional morphology in breast carcinoma. Intratumoral variability of classical morphological signs, such as the growth pattern, the histological grade, cell proliferation, necrosis, microcalcification, angiogenesis, and the immune cell infiltration is also related with the co-existence of hypoxic areas. Thus, a deeper understanding of hypoxia-activated mechanisms is required. The current paper aims to summarize the major tissue factors involved in the response to hypoxia and their potential contribution to the breast carcinoma phenotype.