COW-2021-13

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1. Benign mucinous metaplasia

Benign mucinous metaplasia (BMM) of the penis is rarely reported. It can involve the foreskin or glans penis and is composed of goblet cells distributed in the superficial part of the squamous epithelium. The distribution can range from scattered and infrequent goblet cells to extensive replacement of the surface layer. The cells exhibit bland cytological features with regular cell placement and polarised surface goblet cells with basally located small nuclei. Mitotic figures are not evident. It is usually associated with severe inflammation in the setting of Zoon’s plasma cell balanitis (as in this case, not shown) or penile lichen sclerosus. This supports the theory that it is a metaplastic effect secondary to chronic inflammation and impaired barrier function. It is unrelated to Human papilloma virus infection.

The main differential diagnosis includes primary extramammary Paget’s disease (apocrine intraepidermal adenocarcinoma) and secondary extramammary Paget’ disease (with underlying carcinoma, e.g. urothelial carcinoma). In Paget’s disease the neoplastic cells are randomly distributed within the epithelium and exhibit nuclear atypia, as opposed to BMM. Paget’s disease and BMM show similar or overlapping immunohistochemical staining patterns. However, in BMM CK7 is expressed in a band-like pattern in the mucinous cells only (as in this case), in all suprabasal layers, or the entire thickness of the epithelium; while in Paget’s disease it is expressed in a scattered pattern within preserved squamous epithelium. Also, Ki-67 positive mucinous cells are not seen in BMM but are seen in the superficial epithelial layers in Paget’s disease. Negative melanocytic markers exclude melanoma in situ.

1. Val-Bernal JF, Hernández-Nieto E. Benign mucinous metaplasia of the penis. A lesion resembling extramammary Paget’s disease. J Cutan Pathol. 2000 Feb; 27(2):76-79.

2. Fang AW, Whittaker MA, Theaker JM. Mucinous metaplasia of the penis. Histopathology. 2002 Feb; 40(2):177-179.

3. Böer-Auer A, August C, Falk TM, Jung JE, Kohl K, Metze D. Benign mucinous metaplasia of the genital mucosa: histomorphological and immunohistochemical features and criteria for differentiation from extramammary Paget disease. Br J Dermatol. 2011 Dec; 165(6):1263-1272.

Laurence Galea
Melbourne Pathology
Victoria, Australia
Email: Laurence.Galea@mps.com.au

Penis

Penis, foreskin, mucinous metaplasia, Paget’s disease