Raman spectroscopy, which analyzes molecular vibrations, is a promising new technique for the diagnosis of breast cancer. Haka et al. report the first use of Raman spectroscopy to examine breast cancer in vivo. In their pilot study, Haka et al. performed Raman spectroscopy for intraoperative margin assessment in patients undergoing partial mastectomy surgery for breast cancer. This was accomplished using a portable clinical Raman system with an optical fiber probe of their own design, shown in use during one of the surgical procedures in the lower left panel. Using a previously developed Raman spectroscopic diagnostic algorithm, they detected a grossly invisible cancer at a surgical margin that, upon pathological review, required the patient to undergo a second surgical procedure. The upper two panels show a Raman spectrum obtained from that positive margin, which was involved by ductal carcinoma in situ (above), as well as a spectrum from a negative margin, which was involved by benign fibrocystic change (below). Diagnostic information is obtained by fitting these spectra using a Raman spectroscopic model of breast tissue (model fits are shown in blueand green, respectively). If Raman spectroscopy had been employed in a real-time fashion to guide tissue excision during the partial mastectomy procedures, the additional reexcision surgery might have been avoided in the patient with the positive margin. For details, see the article by Haka et al. on page3317 of this issue.