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Extramammary paget disease

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Extramammary paget disease (EMPD) is a rare type of skin cancer, characterised by a chronic scaly rash of the anogenital areas. EMPD favours elderly women older than age 50 years.

EMPD has two forms, primary and secondary. Primary EMPD accounts for approximately 80% of EMPD. Primary EMPD is thought to originate from cancer cells of either the top layer of the skin (called epidermis), or a type of sweat gland (called apocrine gland) of the epidermis. Secondary EMPD accounts for approximately 20% of EMPD. Secondary EMPD arises from the spreading of underlying internal cancer. Common internal cancers associated with EMPD includes carcinomas of the colon, rectum, bladder, urethra, cervix and prostate.

EMPD presents with a slowly expanding, moist, red, raised rash with a sharp border between normal and involved skin. There may be scattered areas of white scale and erosion, which is often described as “strawberries and cream” appearance. There may be associated itch, bleeding or burning sensation. The vulva in women and the perianal region in men are the most commonly affected areas. Other sites on which EMPD may occur on include the scrotum, penis, perineum and armpits. In patients with secondary EMPD, they may present with findings of an underlying cancer, such as a swollen lymph node.

EMPD is associated with a significantly reduced quality of life. For patients with a secondary internal cancer, delay in diagnosis may lead to cancer progression and metastases.

The diagnosis is usually made by a dermatologist after taking a skin biopsy. Further investigation may be required. In woman, a pelvis and breast examination (and possibly a mammogram) should be performed. In men, a prostate-specific antigen (PSA) and prostate examination should be performed. Further imaging for metastases may also be considered.

Wide local excision or Mohs micrographic surgery is recommended as the first-line treatment for extramammary paget disease. EMPD is often treated with a combination of treatment options, for example:
• Topical imiquimod
• Radiotherapy
• Photodynamic therapy
• CO2 laser
• Topical 5-fluorouracil
Recurrence is common, hence patients with EMPD should be followed up regularly after treatment.

The prognosis for primary EMPD is excellent if appropriately treated. Risk factors that can worsen prognosis include lymph node or vessel invasion, deeper tumour, and possibly, an elevated CEA level. The prognosis for secondary EMPD will depend on the type and aggressiveness of the underlying internal cancer.

Reference
Cooper S.M. & Wojnarowska F. Anogenital (non-venereal) disease. In Dermatology (4th ed.) by Bolognia JL, Schaffer JV and Cerroni L, 2018. Elservier Limited.

This information has been written by Dr Cathy Zhao and Dr Tanumay Raychaudhury
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