[129] Patterns and Utility of Myoepithelial Cell Staining in Ductal Carcinoma In-Situ with Questionable Invasive Mammary Carcinoma

FI Boulos, NM Granja, DL Page. American University of Beirut, Beirut, Lebanon; Vanderbilt University Medical Center, Nashville, TN

Background: Differentiating ductal carcinoma in-situ (DCIS) from invasive carcinoma (IMC) is a recurring issue in breast pathology, and one that potentially carries significant therapeutic and prognostic implications. The tools that have provided greatest assistance in this distinction are immunohistochemical markers of myoepithelial cells (MEC) which are normally present around DCIS and lost in IMC. The expression of MEC markers is not always uniform, however. The purpose of this study is to evaluate myoepithelial cell staining patterns in DCIS and IMC among cases with questionable invasion and hence assess the utility and potential pitfalls of this diagnostic adjunct.
Design: Fifty-nine consecutive cases of DCIS that required resorting to MEC stains for purposes of final diagnosis were retrieved from the files of the Breast Consultation Service at Vanderbilt University Medical Center. All cases were stained for smooth muscle actin (SMA) and p63. Twenty-five cases with available unstained slides were also stained for Smooth Muscle Myosin Heavy Chain (SMMHC) and CD10. Staining was evaluated relative to internal and external controls.
Results: 8 out of 57 cases (14%) did not show any staining in either in-situ or invasive areas. The DCIS in these cases was low-grade (n=3), mixed low and intermediate grade (n=2), intermediate grade (n=2), and high grade (n=1). The DCIS was involving clustered or multiple papillomas in five of eight cases. Twenty-one other cases (37%), five of which containing involved papillomas, had at least discontinuous staining with focal ducts completely negative for MECs. As far as individual stains were concerned, p63 was less often positive compared to SMA, SMMHC and CD10. The latter two mirrored SMA's staining pattern and intensity with little non-specific myofibroblastic staining. Overall, the MEC immunohistochemical stains unequivocally confirmed the diagnosis in 21 of 57 cases. Three cases remained inconclusive and the remaining cases were diagnosed based on the overall Hematoxylin and Eosin impression with marginal help from immunostains.
Conclusions: Myoepithelial stains can be decreased or completely absent in a significant proportion of DCIS. Hence extreme care should be exercised when dealing with suspicious foci in order not to overdiagnose nor overestimate the extent of invasion based on a negative immunostain.
Category: Breast

Monday, March 9, 2009 9:15 AM

Platform Session: Section B, Monday Morning