In vivo MRI and histopathological assessment of tumor microenvironment in luminal-like and basal-like breast cancer xenografts.

Purpose: To explore tumor pathophysiology with special attention to the microenvironment in two molecular subtypes of human breast cancer using in vivo magnetic resonance imaging (MRI) and histopathology. The impact of tumor growth, size, and the influence of estradiol were also investigated. Materials and Methods: Two orthotopic and directly transplanted human breast cancer models representing luminal-like and basal-like molecular subtypes were characterized by dynamic contrast-enhanced MRI and diffusion-weighted MRI. Ex vivo measurements of vascularization, hypoxia, mitoses, and the level of VEGF activations were associated with the calculated in vivo MRI parameters of the tumors. Results: The vascular permeability and perfusion (K^trans) was significantly higher in basal-like compared to luminal-like tumors. These findings were confirmed by a 4-fold higher proliferating microvessel density (pMVD) in basal-like tumors, reflecting the difference in aggressiveness between the subtypes. No effect of tumor growth was observed during 6 days of growth in any of the models; however, large tumors had lower K^trans, higher extracellular extravascular volume fraction (v_e), and more hypoxia than medium-sized tumors. Estradiol withdrawal induced increased K^trans, v_e, and tumor water diffusion (ADC) in luminal-like tumors, corresponding to increased VEGFR2 activation, which is likely to cause increased tumor vessel permeability. Conclusion: These novel data confirm the potential of functional MRI methods to map histopathologically proven changes in breast tumor vasculature and microenvironment in vivo. J. Magn. Reson. Imaging 2012;. © 2011 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]