Photoacoustic imaging holds potential in diagnosis and treatment monitoring of breast cancer, but clinical translation of this technology has often been hindered by bulky and expensive excitation sources. In this work, the potential of a portable, dual-mode multispectral LED-based photoacoustic and ultrasound system (AcousticX) in breast imaging is investigated for the first time. The AcousticX system comprises a linear array ultrasound probe (7 MHz) and two dualwavelength LED arrays (750/850 nm) placed on both sides of the probe. Two experiments were performed to investigate the potential of the system in imaging the breast. In the first instance, interleaved photoacoustic and ultrasound imaging was performed on a semi-anthropomorphic multi-layered 3D breast phantom with possibility to tune oxygen saturation in blood vessel structures. In the second experiment, vasculature of a healthy human breast was imaged in vivo. Skin and multiple vascular features along with its relative oxygen saturation are visualized using photoacoustic imaging and the ultrasound images offered valuable structural information including fat, fibroglandular tissue and pectoral muscles. In human in vivo experiments, we achieved an imaging depth of around 1.7 cm at a display frame rate of 10 Hz, the highest in vivo imaging depth reported in LED-based photoacoustic imaging using a 7 MHz probe. With the capability of providing real-time structural and functional information, AcousticX holds clinical translation potential in non-invasive breast imaging.