Time-resolved fluorescence was used to investigate malignant and normal adjacent breast tissues stained with a conjugate of indocyanine green and octreotate. A marked increase in fluorescence lifetime intensity was seen in the breast cancer sample compared to the normal sample. The fluorescent lifetimes were also investigated and showed similar fluorescence decay curves in stained malignant and normal breast tissue. These results confirm that somatostatin receptors occur on human breast carcinomas, suggest that the presence of somatostatin receptors should be investigated as a marker of breast cancer aggressiveness, and suggest that this conjugate might be used to detect the presence of residual breast cancer after surgery, allowing better assessment of tumor margins and reducing the need for second or repeat biopsies in selected patients. These results may also provide clues for designing future treatment options for breast cancer patients.