Case 1: The full thickness of the epidermis is involved by enlarged dysplastic squamous cells with acanthosis.

Note the paler, larger atypical keratincytes present in all layers of the epidermis. There is a loss of orderly maturation.

Mitotic figures are present at all levels of the epithelium. Note the lichenoid infiltrate (left) and parakeratosis (right), both features seen in Bowen disease.

Bowen disease or squamous call carcinoma in situ. It is considered a precursor lesion to invasive squamous cell carcinoma. Up to 8% of untreated Bowen disease may progress to invasive carcinoma (Busam).

Histologically, features of squamous cell carcinoma in situ are seen, thus, there is full-thickness atypia of the epidermis. Atypical keratinoctyes with pleomorphic nuclei and hyperchromasia, atypical mitotic figures and dyskeratotic keritinocytes are seen in all layers of the epidermis. There is a loss of orderly maturation. Associated inflammation can be perivascular or lichenoid, consisting of lymphocytes or plasma cells. Parakeratosis, hyperkeratosis and acanthosis are also common features (Rapini, Busam).

Often, you might see pagetoid spread of atypical keratinocytes, thus, the differential diagnosis would include melanoma in situ and Paget disease (either mammary or extrammammary). IHC and clinical history will be crucial in arriving at the correct diagnosis.

Predominantly affects Caucasians and arises in the middle-aged or elderly populaiton. Presents as slow growing persistent discrete erythematous lesions which may be scaly or crusted, resembling a dermatitis. The history of a steroid non-responsive dermatosis is typical.

These plaques are usually located on sun-exposed skin, but can arise any in the body especially in the setting of immunosuppression. Note that erythroplasia of Queyrat is squamous cell carcinoma of the glans penis and vulvar intraepithelial neoplasia is squamous cell carcinoma of the vulva, formerly known as Bowen disease of the vulva.