The accumulation of dye near malignant tumors is much greater than the accumulation of dye near benign tissue. So you could tell not only if there was a tumor, but if it was malignant. Without clinical trials, we really won't know for certain. The fluorescing dye, which is currently used in angiography and liver function tests, passes through the human body in less than three minutes. Except for the injection of the dye, the remainder of the optical biopsy technique is noninvasive.
Infrared light is considered safe to humans.
Mammograms are commonly used to detect breast masses which are then biopsied, a procedure that removes a portion of the tumor tissue for testing. Biopsies are performed either with a needle that draws cells from the mass and requires either local or general anesthesia, or by surgery, which requires general anesthesia. The anesthesia alone for a biopsy could have a higher complication rate than the drug we're using. Mammograms themselves have been the subject of serious debate within the medical establishment, as their potential for doing harm must be carefully weighed against their benefits as a cancer screening device in women of different ages. Mammograms rely on X-rays, which can mutate or destroy the tissue they penetrate.