X-ray mammography has been the major imaging modality in breast cancer detection for years, despite its high false diagnosis rate for malignant tumors and harmful radiation. In the last decade, optical imaging has been emerging as a promising method for breast cancer detection. Using near infrared (NIR) light ranging from 690 nm to 900 nm, an optical device can measure functional properties of breast tissue, such as total hemoglobin concentration (HbT) and oxygen saturation (SO2). Cancers tend to have higher levels of HbT because of their greater vascularization, and lower SO2 because of greater oxygen consumption, than normal tissue. Thus the NIR technology could be useful in breast cancer detection. In addition, optical detection is totally noninvasive and safe, and can be low cost. Photonify Technologies Inc. has developed an optical device for real-time two-dimensional mapping of HbT and SO2 in breast tissue. The device has been tested in a pilot clinical study for a group of 50 patients at the Department of Radiology of the Masachusetts General Hospital at Harvard Medical School. Preliminary results suggest that contrast-normalized standard deviations in HbT and SO2 might be good indicators for breast cancer detection. A patient may have a higher risk to have cancer in a breast portion where the normalized standard deviation in either HbT or SO2 is greater than 0.3. We demonstrate 92% diagnostic sensitivity and 66% specificity in detecting ductal carcinoma, either invasive or in situ. The device may potentially be used as an adjunctive tool with mammography to reduce unnecessary biopsies.