PostScript Figure 2 Immunohistochemical ﬁndings in the keratocystoma specimen. The tumour cells strongly stained for AE1/AE3 (A), CK5/6 (B), and p63 (C), or weakly stained for p53 (D) in the keratocystoma case. Inset images show positive cells in the region. All sections are counterstained with haematoxylin (3200). lymphoid element. The tumour cells stained negatively with periodic acid-Schiff (PAS) and Alcian blue. By immunohistochemistry, the tumour cells were diffusely positive for cytokeratins AE1/AE3 and 5/6, focally positive for cyto- keratin 7, and stained strongly for p63, but weakly for p53 (ﬁgure 2). The basal cells of the stratiﬁed epithelium were partially positive for cytokeratin 19. The tumour cells were completely negative for cytokeratins 8/ 18 and 20. Less than 1% of all tumour cells were Ki-67 positive. DISCUSSION Keratocystoma is a rare benign tumour of salivary gland origin whose nomenclature remains to be conﬁrmed. To the best of our knowledge, only four cases, including the present case, have been reported in the English literature.1e4 This type of tumour needs to be differen- tially diagnosed with several tumours of the parotid gland containing squamous cells, including primary and metastatic squamous cell carcinomas, mucoepidermoid carcinoma, squamous metaplasia in certain benign neoplasias and conditions, and cysts.1 In this case there is no evidence of cytological atypia or abnormal mitotic activity in the squamous cell, which is different from squamous cell carcinoma. The absence of incorporated mucous cells by the mucicarmine stain (Alcian blue) and the presence of marked keratinisation are important for separating this tumour from mucoepidermoid carci- noma. The histology of the tumour is J Clin Pathol August 2010 Vol 63 No 8 different from Warthin’s tumour, which presents with cystic spaces surrounded by two uniform rows of cells with centrally placed pyknotic nuclei. The ﬁrst banchial cleft cyst can involve the parotid gland. The cystic spaces are usually lined with squamous epithelium with keratin material ﬁlling the lumen, but pseudo-stratiﬁed columnar epithelium can also be seen. Sebaceous lymphadenoma and non-sebaceous lympha- denoma of the parotid gland need to be excluded. Overexpression of p63 and p53 in the tumour support neoplastic proliferation. We believe that this type of tumour is a true benign cystic neoplasm, not a christoma or trichoadenoma, based on its morphological and immunohistochemical ﬁndings. Take-home messages < A rare case of a benign tumour of the parotid gland, presenting as a kerato- cystoma, is described. < It is believed that only four cases, including the present case, have been reported in the English literature. < Histologically, the tumour consisted mainly of variably sized and shaped cystic lesions ﬁlled with lamellar keratin material and calciﬁcation. < By immunohistochemistry, the tumour cells were positive for cytokeratins, p63 and p53. Acknowledgements We thank J K C Chan (Department of Pathology, Queen Elizabeth Hospital, Hong Kong) for consultation about the present case. Mei-Fang Zhang, Su-Xia Lin, Chun Yi, Jia Fu, Qiu-Liang Wu, Jing-Ping Yun State Key Laboratory of Oncology in Southern China, Department of Pathology, Cancer Center of Sun Yat-Sen University, Guangzhou, China Correspondence to Dr Jing-Ping Yun, Department of Pathology, Cancer Center of Sun Yat-Sen University, 651 East Dongfeng Road, Guangzhou 510060, China; yunjp@mail.sysu.edu.cn Funding The National Natural Science Foundation of China (No. 30471960 and No. 30973506). Competing interests None. Patient consent Obtained. Ethics approval This study was conducted with the approval of the Independent Ethics Committee of the Cancer Center of Sun Yat-Sen University. Provenance and peer review Not commissioned; externally peer reviewed. Accepted 18 May 2010 J Clin Pathol 2010;63:758e760. doi:10.1136/jcp.2010.076521 This paper is freely available online under the BMJ Journals unlocked scheme, see http://jcp.bmj.com/site/ about/unlocked.xhtml REFERENCES 1. Nagao T, Serizawa H, Iwaya K, et al. Keratocystoma of the parotid gland: a report of two cases of an 759