Magnetic resonance imaging (MRI) has proven to be a highly sensitive method for identifying breast cancer and determining the location and extent of tumor in the breast. Diffusion-weighted imaging (DWI) is a new MRI technique that characterizes tissue microstructure in vivo based on the random microscopic motion of water molecules. DWI has the potential to improve the accuracy of breast MRI by providing valuable complementary information. The apparent diffusion coefficient (ADC), a quantitative parameter calculated from DWI, reflects the degree of water mobility in the extracellular space and provides a measure of tissue cellularity. Recent studies have shown that tumor ADC values are significantly lower compared to that of normal tissues and benign lesions, likely due to a higher cellularity in malignant tumors. The objectives of this study are to validate the usefulness of ADC as a discriminator between malignant and normal tissues and to determine whether the ADC value can be a new prognostic factor for patients with invasive disease. In this study, we will evaluate differences in ADC values of cancer, benign lesions, and normal tissue calculated from pre-operative DWI scans of women with invasive breast cancer. We will also assess the prognostic value of ADC for characterizing invasive cancer by comparing ADC measures with pathologic tumor markers such as grade, hormone receptor expression, proliferation (Ki-67), and lymph node involvement. We hypothesize that DWI may provide a valuable complement to standard breast MRI to improve diagnostic accuracy and reduce the number of false positives and unnecessary biopsies performed as a result of breast MRI. We also hypothesize that DWI may help to characterize invasive disease, which would be important for treatment planning and tailoring therapies for individual patients.

Diffusion-weighted imaging (DWI), a specialized form of magnetic resonance imaging (MRI), has shown promise for early detection of treatment response in tumors. DWI measures the mobility of water molecules in vivo and is sensitive to tissue characteristics such as cell density, membrane permeability, and microstructure. DWI studies of the breast have shown decreased diffusivity in malignant breast lesions, primarily attributed to the increased cell density associated with breast tumors. Previous studies have found that the DWI apparent diffusion coefficient (ADC) in tumors increases in response to treatment earlier than detectable changes in tumor size or vascularity found through conventional imaging techniques. This increase in ADC is thought to be due to cell death and necrosis, and may be a valuable early indicator of treatment efficacy. In this study we used DWI to measure the ADC of tumors in patients undergoing preoperative chemotherapy. Serial changes in breast tumor ADC were measured by region-of-interest (ROI) analysis, which involves using a computer program to trace the border of the tumor on an MR image of the breasts and to calculate ADC for the pixels within the region. We compared the changes in tumor ADC throughout treatment with the pathological findings of the removed breast tissue to find the relationship between changes in ADC and the efficacy of treatment. A better understanding of the relationship between changes in ADC and treatment response will allow treatment regimens to be tailored for maximum benefit to the individual patient. This would not only allow the patients to be put on regimens that are more likely to treat the disease, it prevents them from going through toxic treatments that have no survival benefit.