Papillomatous breast lesions with atypical columnar cell features

Area of Science:

• Breast pathology
• Oncology
• Genetics

Background:

• Columnar cell lesions (CCLs) are recognized precursors to breast cancer.
• Intraductal papillomas typically exhibit benign, polyclonal cellular linings.
• The presence of CCLs within papillomas has not been previously documented.

Purpose of the Study:

• To characterize two unique papillary breast lesions exhibiting atypical CCL morphology.
• To compare these lesions with benign intraductal papillomas and those with atypical ductal hyperplasia (ADH)/ductal carcinoma in situ (DCIS).
• To investigate the potential precursor role of these lesions in breast neoplasia.

Main Methods:

• Immunohistochemical staining for estrogen receptor (ER), progesterone receptor (PR), cytokeratin 5 (CK5), and cyclin D1 was performed.
• Comparative analysis of protein expression patterns between the novel lesions and control papillomas.
• Genetic analysis, including assessment for 16q allelic loss, was conducted on available samples.

Main Results:

• The two papillary lesions with flat epithelial atypia (FEA) morphology showed high ER (100%) and cyclin D1 (90%) expression, with low PR and CK5.
• Benign papillomas displayed variable ER/PR expression and higher CK5 expression (10-50%) compared to the FEA lesions.
• The papillary FEA lesion demonstrated 16q allelic loss, a characteristic genetic alteration in low-grade breast neoplasias, unlike most benign papillomas.

Conclusions:

• Two papillomatous breast lesions with atypical columnar cell lesion (CCL) morphology and 16q loss are described.
• The term "papillary FEA" is proposed for these distinct lesions.
• These findings suggest a potential pathway in breast neoplasia involving papillary structures with atypical cellular features.