How is vulvar cancer staged based on tumor size, depth of stromal invasion, and nodal involvement?

Vulvar Cancer Staging

Vulvar cancer is staged surgically using the FIGO 2021 system, which stratifies patients based on depth of stromal invasion (≤1 mm vs >1 mm as the critical threshold for Stage IA vs IB), tumor size, and lymph node involvement (number, laterality, and extracapsular extension). 1

Stage I: Node-Negative Disease

The fundamental distinction in Stage I disease hinges on depth of stromal invasion:

• Stage IA: Tumor confined to vulva/perineum with stromal invasion ≤1 mm, regardless of tumor size

  • These patients have virtually 0% risk of lymph node metastases and do not require inguinofemoral lymph node evaluation 2, 3
  • Simple partial vulvectomy is sufficient treatment 2

• Stage IB: Tumor confined to vulva/perineum with stromal invasion >1 mm

  • Risk of nodal metastases increases significantly: 10.5% at 1.1-2 mm invasion, 11.8% at 2.1-3 mm, and 14.3% at 3-5 mm depth 3
  • Requires inguinofemoral lymph node evaluation 2

Critical Measurement Caveat

The alternative method of measuring depth of invasion (from basement membrane of adjacent most superficial dermal papilla to deepest point of invasion) is more conservative and clinically validated compared to the conventional method, potentially down-staging some patients from IB to IA who show no increased risk of nodal metastasis 4. Digital measurements tend to be >1 mm less than manual micrometer measurements, so measurement technique matters 4.

Stage II: Node-Negative with Local Extension

Tumor extends to adjacent perineal structures (lower urethra, lower vagina, anus) without nodal involvement, regardless of tumor size 1. The 2021 FIGO revision eliminated substages in Stage II for simplification.

Stage III: Node-Positive Disease

Stage III is defined by positive inguinofemoral lymph nodes and has three substages based on nodal characteristics 1:

• Stage IIIA: 1-2 lymph node metastases, each <5 mm
• Stage IIIB: ≥2 lymph node metastases, each ≥5 mm OR 1 lymph node metastasis ≥5 mm
• Stage IIIC: Lymph node metastases with extracapsular spread

Extracapsular extension is the most prognostically significant nodal feature, showing near-significant survival differences compared to intracapsular disease 5. Bilateral nodal involvement does not independently worsen survival compared to unilateral disease with ≥2 positive nodes, which justified its removal from staging criteria 5.

Stage IV: Advanced/Metastatic Disease

• Stage IVA:

  • Tumor invades upper urethra, upper vagina, bladder mucosa, rectal mucosa, or is fixed to pelvic bone
  • OR fixed/ulcerated inguinofemoral lymph nodes

• Stage IVB: Any distant metastases including pelvic lymph nodes 1

Staging Algorithm by Tumor Location

For lateralized lesions ≥2 cm from midline:

• Ipsilateral inguinofemoral lymph node evaluation only (sentinel node biopsy or lymphadenectomy) 2

For central/midline lesions (anterior or posterior):

• Bilateral inguinofemoral lymph node evaluation required 2
• If unilateral sentinel node positive in midline tumor, contralateral groin treatment can be omitted only if contralateral sentinel node or lymphadenectomy is negative 2

Key Prognostic Pitfalls

The 2009 FIGO staging (now superseded) failed to effectively separate survival between Stages I and II (p=0.52), and showed no significant survival differences among Stage III substages based solely on number of positive nodes 5. The 2021 data-derived revision addresses these deficiencies by incorporating cross-sectional imaging findings and using the same lymph node metastasis definitions as cervical cancer 1.

Groin recurrence is nearly uniformly fatal - patients who had omission of inguinofemoral lymphadenectomy when indicated (>1 mm invasion) showed 11.5% groin recurrence with death within 12 months 3. This underscores the critical importance of appropriate nodal evaluation in Stage IB and higher disease.