Cluster designation 5 staining of normal and non-lymphoid neoplastic skin.

BACKGROUND Immunohistochemical staining for cluster designation 5 (CD5) has been found to label a variety of non-lymphoid tumors. METHODS A variety of eccrine, apocrine, follicular, epithelial, and pagetoid lesions were selected and stained with an anti-CD5 monoclonal antibody (Novocastra Labs, Newcastle upon Tyne, UK, clone 4C7) by immunohistochemistry. The intensity of positive cytoplasmic staining was graded semiquantitatively (1+ weak staining, 2+ strong staining). Additionally, the percentage of positive lesional cells was placed in one of four categories: >75%, 25-75%, 1-25%, and <1%. RESULTS Within normal skin, CD5 labeled lymphocytes, apocrine glands, deep dermal eccrine glands, and smooth muscle (weak). The majority of benign and malignant apocrine lesions demonstrated strong focal (36%, n=11)-to-diffuse (64%, n=16) staining. In contrast, labeling of benign eccrine tumors was more focal, tending to localize around ducts (79%, n=19). Microcystic adnexal carcinoma demonstrated focal staining of deeper ductal structures (71%, n=7), whereas desmoplastic trichoepithelioma and basal cell carcinoma showed only rare positive cells. All cases of mammary (n=7) and extramammary (n=8) Paget's disease labeled diffusely for CD5. Pagetoid Bowen's disease (n=6), intraepidermal sebaceous carcinoma (n=3), nor melanoma in situ (n=6) showed any CD5 staining. CONCLUSIONS Immunohistochemical staining for CD5 is extremely useful in the differential diagnosis of pagetoid epidermal lesions and will mark mammary and extramammary Paget's disease, but not pagetoid Bowen's disease, melanoma in situ, or sebaceous carcinoma.