Toss M, Miligy I, Gorringe K, et al. - Given the association of cathepsin V (CTSV/CTSL2), a lysosomal cysteine proteinase that plays a role in extracellular matrix degradation, with poor prognosis in invasive breast cancer (IBC), researchers here examined the prognostic significance of CTSV in ductal carcinoma in situ (DCIS). A well-characterized and annotated cohort of DCIS comprising pure DCIS (n = 776) and DCIS coexisting with IBC (n = 239) was examined for the CTSV protein expression via immunohistochemical assessment. In pure DCIS, 29% of epithelial tumor cells and 20% of surrounding stroma exhibited high CTSV expression. Outcomes revealed a correlation of high expression of CTSV with poor outcome in DCIS and suggested it to be a potential marker to predict DCIS progression to invasive disease.