Breast Cancer Diagnostics
It has been estimated that in 2012 approximately 200,000 new cases of breast cancer will be diagnosed in the United States, resulting in approximately 40,000 deaths.9 The diagnosis of breast cancer (and virtually every cancer) at earlier stages is correlated with an increase in survival rates.10Mammography is a powerful imaging technique for tumor detection; however, it lacks the ability to decipher benign from cancerous tumors, is unable to detect tumors smaller than 1mm,11 misses approximately 20% of breast cancers potentially present at the time of screening, and has an 8-10% false positive rate.12 These drawbacks lead to inaccurate patient diagnosis, which can allow potentially fatal disease progression, or in the cases of over-treatment, unnecessary physical and emotional trauma.13 ELISA, the most common immunoassay for measuring proteins from breast tumors, excised samples, and serum, have a lower detection limit of ~1-10 pM,14 which is not sensitive enough to measure low abundance proteins that could aid in the early and reliable diagnosis of cancer. There is a clear need to develop techniques capable of detecting biomarkers specific for breast cancer that will enable earlier diagnosis of disease, prediction of patient outcome, and improve therapeutic efficacy in a non-invasive manner. Our goals are to utilize the Simoa developed in our laboratory to discover new biomarkers, both proteins and miRNAs, that meet these requirements so that a simple blood test can be implemented.
Two of the most important features of a sensitive biomarker are that it must be both specific and selective for cancer and, ideally, for a specific type of tumor. Several proteins, including cancer antigen 15-3 (CA 15-3), cancer antigen 27-29 (CA 27-29), and carcinoembryonic antigen (CEA), are currently screened in the serum of breast cancer patients for clinical use. Unfortunately, due to an inherent lack of specificity and sensitivity associated with these biomarkers, they are useful primarily for monitoring only the latter stages of disease and not for detection of primary disease or relapse.13-16 Digital ELISA has proven to be effective for the detection of several different types of proteins in serum, including prostate specific antigen (PSA) for monitoring the recurrence of prostate cancer after radical prostatectomy,17 as well as tumor necrosis factor-alpha (TNF-α) and interleukin 6 (IL-6) for monitoring therapeutic efficacy in Crohn’s disease.14,18 The ability to identify and measure proteins specific to breast cancer but occur at levels that are not measurable in blood using standard methods could enable earlier detection of disease and improve therapeutic efficacy. The goals for this portion of the project are to identify proteins that possess these characteristics and to utilize the power of digital ELISA to produce protein fingerprints to create a more sensitive and specific blood test for breast cancer detection and monitoring.