PTEN and ductal breast carcinoma in situ: While by definition a combination of routine H&E and basal cell marker immunostains are sufficient for diagnosis, immunohistochemistry for PTEN also appears to be useful, with regards to the differential diagnosis with HGPIN [47,52,54], given its retained expression in HGPIN and frequent loss in both AIP and intraductal carcinoma [54,58] (Figure 3).