Vulvar adenocarcinoma is an extremely rare form of vulvar malignancy that originates from glandular tissue. Vulvar cancer comprises 5%-8% of gynecological cancers and 0.4% of new cancers in the United States, with increasing incidence. Less than 5% of vulvar cancers are adenocarcinomas, with up to 45% of these cases being secondary, either by metastases, direct extension, or recurrence.

Primary vulvar adenocarcinomas are a heterogenous group and can arise from several anatomic or histologic origins. The most common types are:

• Extramammary Paget disease (EMPD) – The most common subtype, thought to arise primarily from vulvar apocrine glands or, less frequently, secondarily from pagetoid spread from adjacent structures (most often anorectal, urothelial, or genital tract structures). Older White females (average age at diagnosis of 70-75 years) are typically affected and may be asymptomatic or have associated pruritus, burning, or pain.
• Bartholin gland adenocarcinomas – Masses that arise from the deep labial, mucinous Bartholin glands, with fewer than 100 reported cases. Average affected age is 56 years. This adenocarcinoma can be asymptomatic or present with pruritus, ulceration, pain, or bleeding. Most people with this type of tumor present at an advanced stage.
• Mammary-like adenocarcinomas – These originate from vulvar mammary-like glands, which are specialized anogenital glands that share functional and structural similarities to breast tissue and are believed to be modified vulvar eccrine glands. Tumors can arise from these glands that are histologically similar to breast carcinoma. The tissue demonstrates hormonal responsiveness, with immunohistochemistry showing expression of estrogen, progesterone, and HER2 receptors. Histologic subtypes include ductal (most common), lobular, mucinous, secretory, tubule-lobular, and mixed. With fewer than 40 cases reported, mammary-like adenocarcinomas tend to be more aggressive than their breast counterparts, with a 60% metastatic rate, and are often asymptomatic. Mean age at diagnosis is 60-62.5 years.
• Sweat gland adenocarcinomas – A heterogenous group, although an exceedingly rare subtype, that includes apocrine carcinomas, eccrine carcinomas, porocarcinomas, syringomatous carcinomas, adenoid cystic carcinomas, and other adnexal tumor types. Due to their rarity, they are very poorly characterized, although they typically occur during late perimenopause or after menopause and present as vulvar masses.

Other less common etiologies of vulvar adenocarcinoma are clear cell variants, Skene glands, intestinal-type mucosa, adenoid cystic variants, and adenocarcinoma not otherwise specified (NOS).

Risk factors include older age and postmenopausal status. Vulvar adenocarcinomas are typically not human papillomavirus (HPV) associated.