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[129] Monomorphic Epithelial Proliferations (MEPs): A Distinctive Subtype of Epithelial Hyperplasia and Evidence Suggesting They Are the Precursor Lesion of Some Ipsilateral Breast Failure Carcinomas in Patients Treated with Breast Conserving Therapy

NS Goldstein, F Vicini. William Beaumont Hospital, Royal Oak, MI

Background: Why some BCT-treated invasive breast carcinoma patients, including those with adequately-excised, margin-negative initial excisions develop clonally-related ipsilateral breast failures are unknown. We studied a distinctive subtype of epithelial hyperplasia around initial invasive carcinomas, which we term monomorphic epithelial proliferations (MEPs) in regards to a possible relationship with initial or IBF carcinomas.
Design: The unifying and distinctive features of MEPs were slightly-hyperdense overpopulation of highly monomorphic, clonal-like epithelial cells. 70 BCT invasive carcinomas with IBFs were retrieved from our files and the clonal relationship between the initial and IBF carcinomas was established using a 24-marker LOH PCR-assay. The histologic grade, morphology, and the amount of invasive carcinoma and DCIS, and TDLUs with MEPs near (within 5 mm) of the initial excision specimen final margin was recorded. Two BCT, non-IBF cases, matched for carcinoma grade, amount of carcinoma near the margin, and length of follow-up period for each IBF case (n=140) were selected from our files as controls.
Results: The mean number of MEPs around initial excision specimen margins in IBF patients was 5.5 compared to 3.6 in non-IBF patients (p <0.001). Among the subset of patients with negative or near-least amount initial excision specimen margins, the mean number of MEPs in IBF patients was 5.7 compared to 3.3 in non-IBF patients (p<0.001). Patients who developed clonally related IBFs had a higher mean number of MEPs than clonally different IBF patients (6.2 vs 4.1, p=0.056). There was a similar trend in the subset of IBF patients with negative or near-least amount margins (6.4 vs 4.4, p=0.061). The mean number of MEPs near the final margin had no association with invasive carcinoma grade. In clonally related IBF cases, the mean number of identical LOHs in MEPs--initial CAs and MEPs---IBF CAs were 4.1 and 4.5, respectively, compared to mean shared numbers of 2.8 and 3.9 in clonally different IBF cases.
Conclusions: MEPs appear to be the pool of partially transformed clonal lesions from which initial invasive and IBF carcinomas arise. From this perspective, radiation therapy may work to reduce the IBF rate in most patients by eradicating these partially transformed clones and preventing new carcinomas from emerging rather than eradicating microscopic residual disease.
Category: Breast

Monday, March 26, 2007 11:30 AM

Platform Session: Section D, Monday Morning