Columnar cell lesions of the breast: morphologic features and role of 16q losses

Columnar cell lesions of the breast are proposed as the earliest recognizable precursor lesions of low grade breast cancer. The lesions are characterized by cystically enlarged terminal duct lobular units with monotonous (monoclonal) columnar type luminal cells. Variants with and without atypia are recognized.
In her thesis, Mirthe de Boer discusses the morphological, immunohistochemical and molecular features of columnar cells lesions and other benign and premalignant look-alikes.
Morphologically, a new phenomenon of pagetoid “pale cells” is described in columnar cell lesions. These pale cells could potentially serve as a feature of atypia.
The role of chromosome 16q losses in breast carcinogenesis is reviewed and the frequency of chromosome 16q losses is studied in columnar cell lesions, columnar cell look-alikes, other members of the low nuclear grade breast neoplasia family and blunt duct adenosis.
Based on the lack of chromosome 16q losses, blunt duct adenosis is proposed as a separate entity, falling in the spectrum of the benign lesions. Morphological criteria to discriminate between blunt duct adenosis and columnar cell lesions are presented.
Finally, also the overlapping characteristics of columnar cell lesions and intraductal papillomas are discussed and the first papillary atypical columnar cell lesion variants are described.
The results of this thesis underline the precursor role of columnar cell lesions and have the potential to improve accuracy and reproducibility of the diagnosis of early precursor breast lesions, which is the basis for researching optimal patient care.