Mutation and loss of p53 function are common features among human breast cancers. We use BALB/c-Trp53+/- mice as a model to examine the sequence of events leading to mammary tumors. Mammary epithelium proliferation rates were similar in both BALB/c-Trp53+/- mice and wild type controls. Among the 28 mammary tumors collected from BALB/c-Trp53+/- mice, loss of heterozygosity for Trp53 was detected in more than 90% of invasive mammary tumors. Transplantation of Trp53+/- ductal hyperplasias indicated an association between loss of the wild type allele of Trp53 and progression to invasive carcinomas. Expression of biomarkers such as ERα, PR, Her2/Neu and activated Notch1 varied among the tumors suggesting that multiple oncogenic events collaborate with loss of p53 function. The majority of the tumors expressed both luminal and basal cytokeratins (59%). Gene expression analysis showed ligands and receptors of stem cell related pathways, such as Notch and Wnt, were increased in the tumors. These results indicate that mammary tumors in BALB/c Trp53+/- mice might initiate from bipotent mammary progenitor cells. USING MAGNETIC NANOPARTICLES FOR CANCER THERMOTHERAPY Alternating magnetic field (AMF) heating of magnetic nanomaterials provides a promising method for executing therapeutic thermal treatment for cancer patients. In order to explore the potential of magnetic nanoparticles (MNPs) for hyperthermia treatment, we synthesized iron oxide MNPs with various passivation by citric acid, folate, trimethylamine carboxylic acid, or albumin. The albumin passivated MNP (MNP-A) surpassed other MNPs, showing efficient heating with very low inherent cytotoxicity. Confocal microscopy located MNP-A (FITC tagged) accumulation in both cell nucleus and cytosol after 24hr incubation with HeLa cells. The quantity of cell bound MNP-A (including internalized and cell membrane bound MNP-A) was positively associated with MNP-A concentration and incubation time with cells. The MNP-A bound to cells was sufficient to increase the temperature in the cell pellet Δ7°C after 8min exposure to AMF. No significant temperature increase or cell death was detected in control groups. Our data demonstrate that MNP-A provides a selective tool for AMF-induced thermal treatment, as well as useful dosing information for future preclinical animal studies.