Clinging carcinoma: an American perspective.

In 1979, Professor John Azzopardi introduced the term "clinging carcinoma" to describe what he considered to represent examples of ductal carcinoma in-situ (DCIS) characterized by "neoplastic cells . . . limited to the periphery of the containing structures." He emphasized that these lesions can be easily missed "since the alteration is cytological rather than anatomical." Two types of clinging carcinoma were described by Azzopardi. He considered the first to represent a variant of high-grade DCIS, and most pathologists concur with that view. In contrast, pathologists have been much more reluctant to accept Azzopardi's second type of clinging carcinoma as a type of DCIS, particularly in the United States. This second type is characterized by cells with low grade, monomorphic-type cytologic atypia, similar to the cells comprising low-grade DCIS with solid, cribriform, and micropapillary architectural patterns. Recent morphologic, immunophenotypic, and genetic studies have provided strong evidence that this lesion, described by Azzopardi as a type of clinging carcinoma (and now commonly referred to as flat epithelial atypia), does in fact represent a precursor to or an early stage in the development of DCIS, essentially validating the histologic observations made by Azzopardi more than 30 years ago.