Microscopic description and IHC:

Sections show skin with High-Grade Squamous Intraepithelial Lesion (HSIL)/Vulvar Intraepithelial Neoplasia 3 (VIN3). Additional findings include hyperkeratosis, perivascular chronic inflammation, and pigment incontinence. Scattered Intraepidermal large atypical cells are present and reaching the upper third of the epithelium. Immunostains show the cells are positive for CK5, CAM5.2 (focal weak), and negative for S100, Melan-A, CK7.

Discussion:

In addition to confirm the presence of HSIL, immunohistochemical stains are vital in this cases to rule out possible malignant nature of the large atypical cells with pale cytoplasm and pagetoid like spread.

Extramammary Paget's disease (EMPD) presents with large atypical cells with pale, vacuolated cytoplasm. They are usually found in the suprabasal layer and there are no intracellular bridges. Due to high mucin content, PAS stain can be used to highlight the cells. Additionally, the atypical cells are positive for CK7, EMA, and CEA.

Melanoma with pagetoid spread can present with similar morphologic findings. Unlike EMPD, the malignant cells usually also surround the dermoepidermal junction. Melan A, HMB45, S100, and SOX10 are negative in Paget disease but positive in cases of melanoma.

Vulval Intraepithelial Neoplasia (VIN) is a pre-cancerous skin lesion of any part of the vulva and was previously know as Bowen disease of the vulva. VIN is also called know vulvar squamous intraepithelial lesion(SIL). The lesions present as flat erythematous, pale or pigmented patches or a combination of the three, and usually asymptomatic. The lesion usually stains positive for p16, CK5/6 and negative for CAM 5.2, CEA, HMB45, CK7, HER2 and S100.

Growing evidence has established two major types of VIN, which correspond to two distinct oncogenic pathways to vulvar squamous cell carcinoma (VSCC). VIN of usual type (uVIN) is human papillomavirus (HPV)-driven, affects younger women and is a multicentric disease. In contrast, VIN of differentiated type (dVIN) occurs in post-menopausal women and develops independent of HPV infection.

Microscopic image possibly detecting cancerous areas in human tissue
References:

Hoang, Lien N., et al. "Squamous precursor lesions of the vulva: current classification and diagnostic challenges." Pathology 48.4 (2016): 291-302.

Gonçalves Amorim, Andressa, et al. "Paget Disease of the Vulva: Diagnosis by Immunohistochemistry." Case reports in dermatological medicine 2015 (2015).

CASE IMAGES