Abstract (300 words maximum) Each year, over 700 women undergo an image-guided core needle biopsy (CNB) to evaluate a suspicious breast finding at the Seattle Cancer Care Alliance, with only about 30% biopsies yielding malignancy. Typical turnaround time for determination of the presence or absence of cancer from CNBs is three to five business days, and this waiting time can lead to avoidable anxiety and delays in management. Our team has pioneered the use of open-top light-sheet microscopy (OTLS), which is a slide-free fluorescence imaging technique that enables rapid, large area scanning of fresh tissue. A preliminary study using excised 1 cm2 pieces of fresh breast tissue showed that OTLS imaging can provide diagnostic quality images in under 10 minutes. We hypothesize that OTLS evaluation of CNB breast tissue specimens will provide an accurate determination of malignancy vs. no malignancy within 30 minutes of obtaining breast core specimens. We will test this hypothesis by optimizing evaluation of CNB samples with OTLS using breast cancers that have been excised surgically and then testing its accuracy in a small clinical trial of 40 women. If successful, our approach could allow women with concerning breast imaging findings to have a complete imaging and pathology workup in the same day, leading to reassurance in the majority of women and earlier triage to appropriate care in those with breast cancer. Furthermore, wider application of this technology could allow for more accurate whole-specimen evaluation of biomarkers of disease, such as quantification of tumor infiltrating lymphocytes, and more elegant radiology-pathology correlation studies that could advance the emerging fields of radiomics and pathomics.