ALDH1A3 (a.k.a. RALDH3), which catalyzes the formation of retinoic acid (RA), is highly expressed and spatially localized to the myoepithelial layer in DCIS #1, but is reduced in DCIS#2 and invasive regions. The gene discussed is ALDH1A3; the disease is ductal breast carcinoma in situ.