Toss MS, et al. - Given that cathepsin A (CTSA), a key regulatory enzyme for galactoside metabolism, is differentially expressed at the mRNA level between breast ductal carcinoma in situ (DCIS) and invasive breast carcinoma (IBC), researchers characterized the expression of CTSA protein in DCIS and assessed its prognostic importance. CTSA was immunohistochemically stained by a large cohort of DCIS (n=776 for pure DCIS and n=239 for DCIS associated with IBC (DCIS/IBC)) as a tissue microarray. In 48% of pure DCIS, high CTSA expression was observed. Findings suggested an association of high expression with features of poor DCIS prognosis including younger age at diagnosis (<50 years), higher nuclear grade, hormone receptor negativity, HER2 positivity, high proliferative index and high hypoxia inducible factor 1 alpha expression. High CTSA expression was related to a shorter recurrence-free interval (RFI). Overall they concluded that CTSA is not only linked to aggressive behavior and poor results in DCIS, but also a potential marker for predicting the co-existing invasion of DCIS.