Identifying cancer cell-specific binding molecules should greatly improve cancer treatment therapies since many current methods are non-specific, attacking target as well as normal cells. Peptides are an attractive targeting ligand since they are naturally occurring, can be easily produced, and can be tailored to become cancer cell-specific. By modifying an outer membrane protein (Omp A) of the bacterium E. coli to contain random peptides on its surface, selections were performed to isolate peptides that allowed for binding to tumor cells. In addition to OmpA, the bacteria were engineered to express a green fluorescent protein (GFP) that was used as a marker to indicate if bacteria were binding to the tumor cells. These tumor-binding bacteria were isolated and characterized using Fluorescence Activated Cell Sorting (FACS), and the DNA of the bacteria was sequenced to determine the identity of the targeting peptide. Three bacterial clones expressing peptides sequences known to bind breast tumor cells were assayed for their ability to also internalize into the cells. Finding such peptides will benefit cancer research greatly by allowing for more specific, targeted therapies.