Anal and Genital Intraepithelial Neoplasia

Clinical and Pathological Features

Causes and the Two Pathways to Cancer

HPV-Associated Pathway (uVIN / uPIN / uVaIN / uAIN)

• Who is affected: usually young to middle-aged adults (20–50 years), linked to sexual activity or weakened immunity (HIV infection, organ transplant).
• Mechanism: persistent infection with high-risk HPV types, mainly HPV-16 (over 80% of cases), along with HPV-18, 31, 33 and 35.
• Features: the viral oncoproteins E6/E7 inactivate p53 and pRb, releasing p16INK4a, which accumulates and shows strong, diffuse positive staining. Lesions are often multifocal and can affect several sites at once (for example, VIN and AIN together).

HPV-Independent Pathway (dVIN / dPIN)

• Who is affected: usually older women or men (over 60).
• Mechanism: develops on a background of long-standing, scarring chronic inflammation, especially lichen sclerosus or lichen planus.
• Key mutation: a direct mutation of the tumor suppressor gene TP53, with no HPV involvement.
• Outlook: progresses very quickly to invasive squamous cell carcinoma (invasive cSCC), with transformation rates of up to 30–80%, far higher than the HPV-associated type.

Clinical and Histological Grading (LSIL / HSIL)

• LSIL (low-grade squamous intraepithelial lesion / IN-1): mild dysplasia confined to the lower third of the epithelium. It usually reflects a transient HPV infection that clears on its own and is not considered a true precancer.
• HSIL (high-grade squamous intraepithelial lesion / IN-2, IN-3): severe dysplasia involving two-thirds to the full thickness of the epithelium. This is a true precancerous lesion that must be treated.

Microscopic Features (Histopathology)

• Usual type (usual-type HSIL / uVIN / uPIN / uAIN):
  • Bowenoid type: thickened epithelium with atypical keratinocytes that have large, dark nuclei, and abnormal mitoses at every level of the epithelium.
  • Basaloid type: the epithelium is replaced by small, uniform basal-like cells with crowded nuclei and loss of polarity.
• Differentiated type (differentiated-type HSIL / dVIN / dPIN):
  • Difficult to diagnose under the microscope because the atypical cells are confined to the basal and parabasal layers.
  • The upper layers still mature fairly normally, but there is abnormal early keratinization (premature keratinization/dyskeratosis) just above the basal layer.
  • The rete ridges are elongated and branch irregularly deep into the dermis.

Differential Diagnosis and Immunohistochemistry (IHC)

Our Approach to Treating AIN and GIN

At Haute-Derma, we tailor management to each patient based on an accurate classification of the underlying molecular cause:

• Mandatory triage by immunohistochemistry: every AIN/GIN biopsy is stained for p16INK4a and p53 to clearly separate uHSIL (better outlook) from dHSIL (which needs prompt excision with safe margins).
• Preserving structure and function: because these lesions sit in sensitive areas (vulva, penis, anus), we favor tissue-sparing surgery (lesionectomy/Mohs) or photodynamic and topical medical treatment for uHSIL, to avoid contracting scars that impair sexual, urinary or bowel function.
• Multifocal screening: we examine the entire anogenital mucosa, since HPV can cause disease in the vulva, cervix, vagina and anal canal at the same time.

Diagnosing Anogenital Intraepithelial Neoplasia at Haute-Derma

• Detailed Magnified Examination (Vulvoscopy / High-Resolution Anoscopy, HRA):
  • 5% acetic acid is applied to look for areas that turn white (acetowhite lesions).
  • Abnormal vessel patterns are identified on dermoscopy or mucosal examination: dotted vessels, mosaic vessels or atypical hairpin vessels.
• Targeted Skin and Mucosal Biopsy (Punch / Shave Biopsy): taken from the most intensely acetowhite area or where the abnormal vessels are most obvious.
• Mechanism-Defining Immunohistochemistry (p16 / p53): reliably distinguishes uHSIL from dHSIL.
• HPV PCR Genotyping and Screening Cytology (Pap Smear): identifies which high-risk HPV types are present, together with cervical/anal cytology.

Specialized Treatments at Haute-Derma

Treatment is chosen according to the type (uHSIL vs. dHSIL) and the location and extent of the lesion:

• Differentiated Type (dVIN / dPIN, p53 Mutant):
  • Wide local excision or Mohs surgery: the lesion must be fully removed with a safety margin of at least 5 mm because of the very high risk of invasive cancer.
• Usual Type (uHSIL / uVIN / uPIN / uVaIN / uAIN, p16 Positive):
  • UltraPulse CO2 laser ablation: the first choice for multifocal mucosal lesions. The laser precisely vaporizes the diseased epithelium to a depth of 1.5–2 mm (below the base of the hair follicles in hair-bearing areas) without leaving flat, hard scars.
  • Topical immune modulator (imiquimod 5%): applied 2–3 times a week for 12–16 weeks. It stimulates the local immune system to clear HPV-infected cells, works well for uHSIL and leaves the anatomy of the vulva or penis fully intact.
  • Topical chemotherapy (5-fluorouracil / 5-FU 5%): used for VaIN (vagina) or AIN (anal canal) under close medical supervision.
  • Photodynamic therapy (PDT): the photosensitizer 5-ALA is applied and then activated with a dedicated red light. Well suited to large uHSIL patches around the anus and perineum.