In this paper, I will provide a broad review of breast cancer research conducted at the University of Pennsylvania and collaborative work with other institution. Our group led by Dr. Arjun G. Yodh has been actively exploring functional and physiological information available via the diffuse optical technique and investigate its use in the area of in vivo breast cancer detection, diagnosis, and therapy monitoring. In particular, the recent advances in malignant and benign lesion differentiation from 3D diffuse optical tomography, 3D fluorescence diffuse optical tomography using Indocyanine Green injection, and neoadjuvant chemotherapy monitoring with diffuse correlation spectroscopy will be presented.