For the past decade, Dr. Jeffrey's lab has performed molecular profiling of cancer cells with the goal of identifying tumor-specific therapies for the personalized treatment of cancer.

She was a member of the collaborative Stanford/Norway team that pioneered the use of DNA microarrays to measure global gene expression in solid tumors, and was involved in the development of the currently accepted classification schema for breast cancer subtypes based on gene expression profiles- such as low and high proliferation luminal, ERBB2(HER2)-overexpressing, and basal-like breast cancers (which then focused attention on triple negative breast cancers). Her laboratory refined RNA amplification techniques and developed expertise in the transcriptional profiling of tiny quantities of tumor tissue and in RNA isolation from formalin-fixed paraffin-embedded samples.

Her research currently involves extracting and profiling circulating tumor cells (CTCs) from blood and bone marrow to shed light on the metastatic process and eventually to help guide selection of appropriate therapies in individual cancer patients. To facilitate this, Dr. Jeffrey and colleagues from the School of Engineering and Genome Technology Center invented a new technology, the MagSweeper, an automated immunomagnetic separation device that isolates live rare cells from blood with high purity and minimal impact on gene expression. Her lab performs high dimensional single cell analyses on CTCs to investigate how transcriptional profiles or mutational status of different CTC populations relate to metastases and drug response, particularly for newer therapies under development or in Phase I/II clinical trials. CTCs being studied include those from patients with cancers of the breast, prostate, lung, pancreas, and liver. Dr. Jeffrey's lab is also funded to perform preclinical testing on patient-derived xenograft models to identify molecular phenotypes of breast cancer that may be targeted by epigenetic pathway inhibitors drugs, working with colleagues at University of Utah to determine how these newer therapies may be best applied to different subtypes of breast cancer.

In the past, Dr. Jeffrey worked with Dr. Robert Mah at NASA Ames Research Center to study multiplex in-vivo physiologic attributes of breast tumors in real-time using a multisensor NASA Smart Probe that she co-developed with Dr. Mah. It is hoped that future studies will associate real-time physiological features with tumor and CTC profiles for intelligent drug selection.