J Cutan Pathol 2011: 38: 871 – 875 doi: 10.1111/j.1600-0560.2011.01780.x John Wiley & Sons. Printed in Singapore Copyright © 2011 John Wiley & Sons A/S Journal of Cutaneous Pathology Expression of laminin-5 γ2 chain in cutaneous pseudocarcinomatous hyperplasia Background: Since the use of laminin-5 as a marker of invasiveness has been proposed by several authors, our objective was to compare the expression of this protein in pseudocarcinomatous hyperplasia and squamous cell carcinoma (SCC). Methods: Sixty-four paraffin-embedded skin biopsy samples with diagnosis of epidermal hyperplasia (non-pseudocarcinomatous), pseudocarcinomatous hyperplasia, actinic keratosis/carcinoma in situ, microinvasive and frankly invasive SCC were obtained for immunohistochemical study. Results: Adjacent normal epithelium and epidermal hyperplasia (non-pseudocarcinomatous) showed no staining. In pseudocarcinomatous hyperplasia, laminin-5 was positive, at least focally, in 14 of 16 (87.5%) samples and was concentrated in peripheral cells of elongated rete pegs and in migrating cells in dermis. In samples of microinvasive carcinoma (n = 7), the expression was observed in all cases and was concentrated in the leading edge of the tumor. All cases (n = 21) of frankly invasive SCC showed cells expressing laminin-5, at least focally. Well-differentiated areas of the tumor presented a pattern of expression in peripheral cells of tumor nests while a diffuse pattern of expression was observed in less differentiated areas. Conclusion: We showed that cytoplasmic laminin-5 expression should not be used as a criterion of malignancy and is not useful in distinguishing pseudocarcinomatous hyperplasia from microinvasive and well-differentiated SCC. Keywords: immunohistochemistry, laminin, laminin-5 γ2, pseudocarcinomatous hyperplasia, skin dos Santos AM, Carneiro FP, Queiroz AJR, Damasceno EAM, de Castro TMML, de Amorim RFB, Takano GHS, Junqueira MIMB, de Magalh˜ aes AV. Expression of laminin-5 γ2 chain in cutaneous pseudocarcinomatous hyperplasia. J Cutan Pathol 2011; 38: 871 – 875. © 2011 John Wiley & Sons A/S. Aline M. dos Santos, Fabiana P. Carneiro, Amadeu J. R. Queiroz, Emanuel A. M. Damasceno, T´ ercia M. M. L. de Castro, Rivad ´ avio F. B. de Amorim, Gustavo H. S. Takano, Maria I. M. B. Junqueira and Albino V. de Magalh˜ aes Department of Pathology, University Hospital of Brasília, Brasília, Brazil Fabiana Pirani Carneiro, MD, Centro de Anatomia Patol´ ogica, Hospital Universit´ ario de Brasília, UNB, Via L2 Norte, SGAN 604/605, M´ odulo C, Brasília DF, CEP: 70840-050, Brazil Tel: +55 61 3448 5499 Fax: +55 61 3107 1907 e-mail: fabianapirani@hotmail.com Accepted for publication January 10, 2011 Pseudocarcinomatous epidermal hyperplasia consists of an exuberant proliferation of epithelium with downgrowth into the dermis and occurs in response to underlying infectious, inflammatory and neoplas- tic conditions. 1–4 The histopathological features of pseudocarcinomatous hyperplasia may simulate well- differentiated squamous cell carcinoma (SCC), but some features of carcinoma, including nuclear atypia; atypical mitotic figures; enlarged, hyperchromatic or pleomorphic nuclei; dyskeratosis; and vascular, lymphatic or perineural invasion are not usually seen with pseudocarcinomatous hyperplasia. 5,6 The identification of an underlying disorder is also use- ful in excluding SCC in difficult cases. However, 871