Tumor Microenvironment–Released Peptides: Could They Form the Basis for an Early-Diagnosis Breast Cancer Test?

Despite expectations that cancer biomarkers could revolutionize cancer diagnosis and treatment, this promise did not bear fruit (1). That is because cancer-specific circulating biomarkers in serum capable of being measured with a simple technique and identifying cancer in noncancer patients with high sensitivity and specificity have not yet been found. The relatively few clinical biomarkers currently used are more useful for patient management than for early diagnosis or population screening (2). Given that some cancers are relatively rare (e.g., ovarian cancer), a screening test for early diagnosis must have an extremely high specificity (e.g., >99%) and a sensitivity sufficient (e.g., >80%) to achieve a reasonable positive predictive value (e.g., ≥10%) (3). Prostate-specific antigen, the most studied screening cancer biomarker for prostate cancer, has recently been reexamined in prospective clinical trials, and the results are controversial (4–6). That is why the US Preventive Services Task Force does not currently recommend routine screening for prostate cancer (7).Currently available breast cancer biomarkers in the circulation, such as CA15–3 and the associated antigen CA27.29, which recognize different epitopes on the same antigen (mucin 1), have relatively poor characteristics, such as a 30% sensitivity for early-stage disease, 60%–70% sensitivity in advanced cases, and increased values in patients with benign conditions, including ovarian cysts, benign breast diseases, and benign liver diseases. Carcinoembryonic antigen has similar limitations. These biomarkers do not have a place in early-disease diagnosis or in population screening (8).The most widely used screening method for breast cancer is mammography. This procedure is not recommended for women younger than 40 years. For older women, its use is controversial, because women with …