A European classification system of DCIS recognized clinging pattern as another variant of DCIS (4) and by using Azzopardi's criteria recommended a separation between well-differentiated (monomorphic variant with low-grade atypia) and poorly differentiated (pleomorphic variant with high-grade atypia) clinging DCIS. (4) The situation in the United States was, however, different.
Moreover, many pathologists were uncertain about the true neoplastic nature of atypical epithelial cells lining the ducts, particularly in the well-differentiated or monomorphic variant (with mild nuclear atypia) of clinging DCIS (F.
After publication of the first molecular-genetic study6 on the issue of clinging DCIS in 2000, it became clear that both variants of this type of flat lesion represent neoplastic alterations of the breast and share many similarities with other more conventional patterns (types) of DCIS.