Vulvar intraepithelial neoplasia is a premalignant lesion of the vulva frequently encountered by gynecologic providers. There has been an increase in the incidence of VIN in younger women in recent decades thought be to be secondary to human papillomavirus infection, cigarette smoking, and sexual behavior (J Reprod Med. 2000 Aug;45[8]:613-5).
Data from the Surveillance Epidemiology and End Results (SEER) database were significant for a 411% increase in the incidence of in situ carcinoma and a 20% increase in invasive vulvar carcinoma from 1973 to 2000 (Obstet Gynecol. 2006 May;107[5]:1018-22). In addition, younger age groups are seeing an increase of in situ disease until age 49. Vulvar cancer however, continues to be a disease of older age.
Terminology
Previously, the term vulvar intraepithelial neoplasia followed the cervical intraepithelial neoplasia (CIN) designation in the 1960s. Conventions for grading these lesions have changed over time. Most recently, in 2004, the International Society for the Study of Vulvar Disease (ISSVD), composed of dermatologists, pathologists, and gynecologists, agreed to change the classification of squamous VIN from the previous VIN 1-3 classification system. The committee described VIN in two forms, “usual type” and “differentiated type” (J Reprod Med 2005;50:807-10).
Dr. Paola A. Gehrig
In making this transition, it was recognized that VIN 1 is not in fact an oncogenic lesion and is now solely referred to as condyloma acuminatum. Grade 2 and 3 are now collectively referred to as VIN. These changes made by the ISSVD reflect the current literature on grading of VIN. In addition to VIN 1 not having any progression to malignancy, it is a diagnosis that is difficult to reproduce and may, at times, reflect reactive changes or other dermatosis. VIN 2 and 3 are not discriminated from each other in a reproducible manner and clinically have no reason for individual distinction (J Low Genit Tract Dis. 2006 Jul;10[3]:161-9).
VIN, usual type is the most common intraepithelial lesion and is historically referred to as classic VIN or Bowen’s disease. This type is associated with HPV infection and includes the formerly described warty type, basaloid type, and mixed type. The carcinogenic subtypes of HPV, 16, 18, 31, and 33 are the most common HPV subtypes responsible. It should be noted, however, that diagnosis is morphological and not based on HPV testing. Usual type is also traditionally thought to be more closely associated with risk factors such as smoking and immunocompromised states.
VIN, differentiated type is not associated with the HPV virus and is frequently found in older women. This lesion is often associated with other dermatologic conditions such as lichen sclerosis and lichen simplex chronicus. Diagnosis is also made by histology with abnormal cells being confined to the parabasal and basal portion of the rete pegs. This type also finds genetic alterations that are seen in invasive squamous cell carcinoma (Appl Immunohistochem Mol Morphol 2001;9:150-63). Differentiated type is thought to be a precursor for HPV-negative keratinizing squamous cell carcinoma of the vulva (Am J Surg Pathol. 2000 Mar;24[3]:429-41).
Dr. Daniel L. Clarke-Pearson
As awareness of this distinct form of VIN increases and more is learned about the precursors of HPV-negative squamous cell carcinoma, physicians are encouraged to closely follow up hyperplastic lesions and lichen sclerosis with biopsies and excision. The diagnosis of differentiated VIN is rarely made at present; however, this distinction by the ISSVD may improve the ability of clinicians and pathologists to recognize this HPV-negative precursor before squamous cell carcinoma is present.
The Lower Anogenital Squamous Terminology project of the College of American Pathology and the American Society for Colposcopy and Cervical Pathology advocates for more consistent terminology across lower anogenital tract lesions. This terminology applies only to HPV-related lesions (usual type) and considers the VIN 1 or condyloma accuminatum to be a low-grade lesion (LSIL), and VIN 2-3 or usual type to be high-grade lesions (HSIL) (Int J Gynecol Pathol. 2013 Jan;32[1]:76-115).
Many clinicians and pathologists have not adopted this most recent terminology; however, there is evidence that the ISSVD classification is the most clinically relevant.
Diagnosis
The majority of patients with any VIN will present with complaints of vulvar pruritus. However, women can also present with pain, burning, or dysuria, or can have an asymptomatic lesion found on pelvic exam. There are no recommended screening strategies to diagnose early VIN. Cytologic testing is complicated by the keratinization of the vulva, making this an unreliable diagnostic assessment.
On physical exam, VIN can have a heterogeneous presentation including papules, plaques, color variations, or ulcer. Differentiated type is thought to have a more defined appearance that frequently develops in the setting of other vulvar dermatosis. These are distinct, solitary lesions that are commonly raised, can have an overlying scale, and have ill-defined borders. A distinct lesion with ulceration or erosion is concerning for invasion.