[187] Immunohistochemical Staining Patterns of Low-Grade Adenosquamous Carcinoma (LGASC) Different from Other Small Glandular Proliferations of the Breast (SGPB).

Kathy Kawaguchi, Sandra J Shin. Weill Cornell Medical College, New York, NY

Background: Background: LGASC is a diagnosis made exclusively on morphologic features. As an uncommon entity, LGASC is readily mistaken for other SGPB including invasive, well-differentiated duct carcinoma, syringomatous adenoma, and radial sclerosing lesion. While immunohistochemical (IHC) staining characteristics have been elucidated in other SGPB, the same have not been established for LGASC, largely due to seemingly inconsistent staining patterns observed not only within individual but also among consecutive cases. We set out to characterize IHC staining patterns of LGASC using commonly employed IHC stains used in the work-up of SGPB.
Design: 29 LGASC cases were retrieved from our files. The diagnosis was confirmed in each case. IHC stains for myoepithelial (M) markers (p63, Smooth Muscle Myosin [SMM], CD10, Calponin and SMA) and cytokeratins (CK) (CKAE1/3, CK7, Cam 5.2, CK 5/6, K903) were performed. Staining patterns within lesional epithelium and adjacent stroma for each stain were recorded.
Results: The glandular epithelium and adjacent stroma variably stained with M and CK markers. For M markers, lesional glands demonstrated circumferential staining in most (>80%) cases with either complete (∼75%) or weak, discontinuous (∼35%) staining using any one stain. In the adjacent stroma, “lamellar” staining was seen in ∼45% of cases using any one stain (Fig a-SMM). Diffuse stromal positivity was seen in >50% of cases with CD10, Calponin and SMA whereas no such staining was seen with p63 and in ∼ 12.5% of cases with SMM. For CKs, lesional glands stained for one or more stains in all cases. Staining was diffuse with either uniform or variably intensity in >75% of cases. In addition, all stains demonstrated “core” staining in 25% to 67% using any one stain (Fig b-K903). The stroma was negative in almost all cases for CKs.

Conclusions: LGASC stain “inconsistently in a consistent fashion” for M and CK IHC stains commonly employed in the work-up of SGPB. These are staining patterns unique to LGASC and help distinguish it from other SGPB.
Category: Breast

Wednesday, March 2, 2011 1:00 PM

Poster Session VI # 19, Wednesday Afternoon


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