# Extramammary Paget Disease > Extramammary Paget disease for NEET-PG Dermatology covering Paget cells, primary and secondary forms, internal cancer screening and excision margins. - Canonical URL: https://prepelephant.com/topics/neet-pg/dermatology/extramammary-paget-disease - Exam / course: NEET-PG · Subject: Dermatology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-14 - Last updated: 2026-10-14 - Reference basis: Rook's Textbook of Dermatology; Fitzpatrick's Dermatology; Andrews' Diseases of the Skin - How to cite: "Extramammary Paget Disease", PrepElephant, https://prepelephant.com/topics/neet-pg/dermatology/extramammary-paget-disease ## Direct answer Extramammary Paget disease is an intraepidermal adenocarcinoma in which Paget cells spread through the epidermis of apocrine-rich areas, mainly the vulva, scrotum, penis or perianal skin. It presents as a sharply demarcated, erythematous, eczema-like plaque that may itch, burn or bleed, and in a minority it signals an internal malignancy. Wide excision with histological margin control is the main treatment, with imiquimod or photodynamic therapy for limited or recurrent disease. ## What you must remember - **Cell type:** Paget cells, large round cells with pale cytoplasm and atypical nuclei, lie within the epidermis; the lesion is an in situ adenocarcinoma. - **Sites:** the anogenital region in both sexes, including the vulva, scrotum, penis and perianal skin; the axilla is a less common site. - **Clinical look:** a well-demarcated, erythematous, moist, scaly plaque that often persists despite topical steroids and antifungals. - **Primary versus secondary:** primary disease arises in the epidermis or adnexa, while secondary disease extends from an internal adenocarcinoma of the rectum, urethra, bladder or prostate. - **Immunohistochemistry:** CK7 and GCDFP-15 are positive in primary disease; CK20 and CDX2 positivity suggests a colorectal source. - **Screening:** colonoscopy, cystoscopy and urological or gynaecological review exclude an associated internal tumour. - **Treatment:** wide local excision or Mohs surgery with margin control, with imiquimod or photodynamic therapy for limited or recurrent disease. ## From a red anogenital plaque to a clean margin A persistent, sharply bordered plaque in the anogenital region that fails topical therapy should prompt biopsy. The steps below cover diagnosis, screening and surgery. 1. **Recognise the plaque:** a well-demarcated, eczematous, erythematous area that does not settle with steroids. 2. **Biopsy with depth:** a punch biopsy showing Paget cells in the epidermis, often with pagetoid spread, confirms the diagnosis. 3. **Stain the lesion:** CK7 and GCDFP-15 favour primary disease, while CK20 or CDX2 positivity points to a colorectal origin. 4. **Screen for internal malignancy:** colonoscopy, cystoscopy and urological or gynaecological assessment look for an associated tumour. 5. **Map the margins:** the disease often extends beyond the clinical border, so the margins must be planned before excision. 6. **Operate with margin control:** wide local excision with histological margin assessment, or Mohs surgery, is the standard approach. 7. **Follow up closely:** recurrence is common, so regular examination and re-evaluation of any new internal symptoms are essential. ## Where the exam tries to catch you Extramammary Paget disease is frequently mistaken for a benign inflammatory dermatosis. - **Trap:** treating an anogenital eczematous plaque as eczema or candidiasis without biopsy. **Correct:** a persistent, sharply marginated plaque that fails topical therapy needs biopsy to look for Paget cells. - **Trap:** stopping the work-up after a lesion looks primary. **Correct:** an internal adenocarcinoma must be excluded, since secondary disease is linked to rectal, urethral, bladder or prostatic tumours. - **Trap:** using a narrow clinical excision because the borders look clear. **Correct:** subclinical spread is common, so histological margin control or Mohs surgery is preferred. - **Trap:** treating it as a benign dermatosis with steroids. **Correct:** it is an in situ adenocarcinoma, and steroids only mask the lesion. ## Frequently asked questions ### What are Paget cells in extramammary Paget disease? Paget cells are large, round cells with pale cytoplasm and atypical nuclei that lie within the epidermis. Their presence in an anogenital plaque, confirmed on biopsy, establishes the diagnosis of extramammary Paget disease. ### Which investigations exclude an internal malignancy in extramammary Paget disease? Colonoscopy and cystoscopy, along with urological or gynaecological assessment, look for an underlying adenocarcinoma in extramammary Paget disease. Immunostains such as CK20 and CDX2 may also suggest a colorectal origin in suspected secondary disease. ### How does primary extramammary Paget disease differ from the secondary form? Primary extramammary Paget disease arises from the epidermis or adnexal structures without an internal tumour. The secondary form extends from an internal adenocarcinoma of the rectum, urethra, bladder or prostate, which changes the work-up and prognosis. ### Why is Mohs surgery used for extramammary Paget disease? Mohs micrographic surgery checks margins at each stage, which suits a disease that spreads beyond its clinical border. It is particularly useful where tissue must be conserved, such as on the penis or in the perianal region. ### Which topical drugs are used for extramammary Paget disease? Imiquimod and photodynamic therapy are used for limited or recurrent extramammary Paget disease, particularly when surgery is not feasible. They are adjuncts rather than replacements for surgical excision, because they may not clear subclinical spread.