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Abstract Purpose of Review Brain metastasis is a significant cause of mortality in breast cancer patients and treatment options are limited. This article will focus on the dynamic intercellular communication between metastatic cancer cells, the tumor microenvironment, and neighboring brain cells to breach the brain’s defenses and promote tumor progression. Recent Findings Recent advances have further elucidated how tumor cells traverse through the blood–brain barrier and implicated the blood–cerebrospinal fluid barrier as a potential entry point. Tumor cells once within the brain milieu utilize factors secreted by and dynamically reprogram neurons, glial cells, and infiltrating leukocytes for their own colonization and survival. Summary Current research has illuminated key mechanisms metastatic breast cancer cells utilize to infiltrate the brain and assimilate in their new environment. New multimodal treatments are investigating not only chemotherapy and radiation that can target metastatic tumor cells, but also immune checkpoint inhibitor–based therapies to sensitize the immune microenvironment.

To develop an MR multitasking-based dynamic imaging for cerebrovascular evaluation (MT-DICE) technique for simultaneous quantification of permeability and leakage-insensitive perfusion with a single-dose contrast injection.MT-DICE builds on a saturation-recovery prepared multi-echo fast low-angle shot sequence. The k-space is randomly sampled for 7.6 min, with single-dose contrast agent injected 1.5 min into the scan. MR multitasking is used to model the data into six dimensions, including three spatial dimensions for whole-brain coverage, a saturation-recovery time dimension, and a TE dimension for dynamicmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:miT/mml:mimml:mn1/mml:mn/mml:msub/mml:mrowmml:annotation$$ {\mathrm{T}}_1 $$/mml:annotation/mml:semantics/mml:mathandmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubsupmml:miT/mml:mimml:mn2/mml:mnmml:mo*/mml:mo/mml:msubsup/mml:mrowmml:annotation$$ {\mathrm{T}}_2^{\ast } $$/mml:annotation/mml:semantics/mml:mathquantification, respectively, and a contrast dynamics dimension for capturing contrast kinetics. The derived pixel-wisemml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:miT/mml:mimml:mn1/mml:mn/mml:msubmml:mo//mml:momml:msubsupmml:miT/mml:mimml:mn2/mml:mnmml:mo*/mml:mo/mml:msubsup/mml:mrowmml:annotation$$ {\mathrm{T}}_1/{\mathrm{T}}_2^{\ast } $$/mml:annotation/mml:semantics/mml:mathtime series are converted into contrast concentration-time curves for calculation of kinetic metrics. The technique was assessed for its agreement with reference methods inmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:miT/mml:mimml:mn1/mml:mn/mml:msub/mml:mrowmml:annotation$$ {\mathrm{T}}_1 $$/mml:annotation/mml:semantics/mml:mathandmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubsupmml:miT/mml:mimml:mn2/mml:mnmml:mo*/mml:mo/mml:msubsup/mml:mrowmml:annotation$$ {\mathrm{T}}_2^{\ast } $$/mml:annotation/mml:semantics/mml:mathmeasurements in eight healthy subjects and, in three of them, inter-session repeatability of permeability and leakage-insensitive perfusion parameters. Its feasibility was also demonstrated in four patients with brain tumors.MT-DICEmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:miT/mml:mimml:mn1/mml:mn/mml:msubmml:mo//mml:momml:msubsupmml:miT/mml:mimml:mn2/mml:mnmml:mo*/mml:mo/mml:msubsup/mml:mrowmml:annotation$$ {\mathrm{T}}_1/{\mathrm{T}}_2^{\ast } $$/mml:annotation/mml:semantics/mml:mathvalues of normal gray matter and white matter were in excellent agreement with reference values (intraclass correlation coefficients = 0.860/0.962 for gray matter and 0.925/0.975 for white matter ). Both permeability and perfusion parameters demonstrated good to excellent intersession agreement with the lowest intraclass correlation coefficients at 0.694. Contrast kinetic parameters in all healthy subjects and patients were within the literature range.Based on dynamicmml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"mml:semanticsmml:mrowmml:msubmml:miT/mml:mimml:mn1/mml:mn/mml:msubmml:mo//mml:momml:msubsupmml:miT/mml:mimml:mn2/mml:mnmml:mo*/mml:mo/mml:msubsup/mml:mrowmml:annotation$$ {\mathrm{T}}_1/{\mathrm{T}}_2^{\ast } $$/mml:annotation/mml:semantics/mml:mathmapping, MT-DICE allows for simultaneous quantification of permeability and leakage-insensitive perfusion metrics with a single-dose contrast injection.