MONOCLONALITY IN FIBROADENOMAS WITH COMPLEX HISTOLOGY AND PHYLLODAL FEATURES

Fibroadenoma is a common cause of benign breast masses in young women. These women have a slightly increased risk of subsequent breast cance r, particularly if their tumors have complex histologic patterns. We a ssessed monoclonality in fibroadenomas and correlated the results with histologic analysis. We performed a clonal analysis of 52 fibroadenom as from 43 patients using X-chromosome inactivation studies. The cases included fibroadenomas with complex and simple histology. Areas exami ned were predominantly stroma but epithelium was also present. DNA was isolated from paraffin-embedded tissue and was subjected to polymeras e chain reaction amplification of the human androgen receptor gene wit h and without predigestion of the DNA with Hha 1. If a monoclonal proc ess was identified, the epithelial and stromal components were subsequ ently microdissected and reanalyzed. 36/43 (83.7%) women were heterozy gous. We studied 45 tumors in these 36 informative women. 1/20 (5% com plex fibroadenomas and 1/25 (4%) simple fibroadenomas were monoclonal. The epithelial component of both monoclonal fibroadenomas was polyclo nal. The one monoclonal simple fibroadenoma was also the only one with mixed features to contain a phyllodes component. In this case, monocl onality was found in the stroma of both the fibroadenoma and phyllodes regions. Monoclonality has been previously associated with phyllodes phenotype, but not with fibroadenomas, except for 3 fibroadenomas that recurred as phyllodes tumor. We report that monoclonality may also be seen occasionally in complex fibroadenomas, and was found in a tumors with mixed fibroadenoma/phyllodes features without clinical recurrenc e for 4 years.