The Importance of p16 and p53 Immunohistochemical Staining in Diagnosing Vulvar Lichen Simplex Chronicus Mimicking Vulvar Intraepithelial Neoplasia with False-Positive Human Papillomavirus Type 66.

Vulvar intraepithelial neoplasia (VIN), the precursor lesion of vulvar squamous cell carcinoma (VSCC), may present as pruritic or asymptomatic lichenified plaques surrounded by single or multiple discrete or confluent macules or papules. VIN is divided into high-grade squamous intraepithelial lesion (HSIL), which is human papillomavirus (HPV)-driven, and differentiated VIN (DVIN), which develops independently of HPV. Histopathological examination and HPV genotyping polymerase chain reaction (PCR) tests should be performed to distinguish between HSIL and DVIN. Lichenified plaques surrounded by multiple papules are found not only in VIN but also in vulvar lichen simplex chronicus (LSC). This chronic inflammatory skin disease mostly appears in labia majora and is triggered by sweating, rubbing, and mental stress. IHC staining of p16 and p53 are recommended as the most commonly used biomarkers for VIN in diagnostically challenging cases. IHC staining is also beneficial to confirm the accuracy of the HPV detection technique, as p16-negative staining may also represent a false-positive result. We report a case of the importance of p16 and p53 IHC staining in diagnosing vulvar LSC mimicking VIN with false-positive HPV-66. The patient was previously diagnosed with VIN based on clinical examination. HPV-66 was detected by PCR from a vulvar biopsy sample. Histopathological examination revealed stromal lymphocytic infiltration with non-specific chronic dermatitis; neither atypia nor koilocyte was observed. Both p16 and p53 IHC staining were negative. The patient was diagnosed and treated as vulvar LSC with 10 mg cetirizine tablet, emollient, and 0.1% mometasone furoate cream. Clinical improvement was observed as the lesions became asymptomatic hyperpigmented macules in the 4 weeks of follow-up, without recurrence after 3 years of follow-up. Both p16 and p53 IHC staining might help distinguish HSIL and DVIN mutually and from other vulvar mimics in diagnostically challenging cases.