Given a >2 cm auricular skin cancer with 4 mm depth of invasion but negative lymph‑vascular invasion (LVI) and negative perineural invasion (PNI), is adjuvant radiotherapy recommended?

Adjuvant Radiotherapy is NOT Recommended

For a >2 cm auricular skin cancer with 4 mm depth of invasion but negative LVI and negative PNI, adjuvant radiotherapy is not indicated after complete surgical excision with adequate margins.

Rationale Based on Evidence

The absence of both lymphovascular invasion (LVI) and perineural invasion (PNI) fundamentally changes the risk profile of this tumor, even with its size and depth characteristics.

Key Evidence Supporting Observation

Most recent high-quality data from auricular cSCC specifically shows excellent outcomes with surgery alone when high-risk pathologic features are absent 1. In a 2022 cohort of 178 patients with primary auricular cSCC:

• 93% were AJCC stage I, 6% were stage II
• 97% underwent Mohs micrographic surgery alone
• 3-year local recurrence was only 1% (95% CI 0-5%)
• Critically: Among 10 patients upstaged to pT3 disease (depth >6 mm) who underwent MMS alone, NONE recurred locoregionally
• Advanced stage, PNI, and LVI were the only factors significantly associated with increased recurrence risk

Why LVI and PNI Status Matters More Than Size/Depth

Multiple guidelines and recent research consistently identify PNI and LVI as the critical adverse features that trigger adjuvant radiotherapy recommendations:

• ASCO 2025 guidelines 2 for oropharyngeal cancer (applicable principles): Adjuvant RT is indicated specifically for close margins, PNI, or LVI (moderate evidence, strong recommendation)

• 2021 meta-analysis 3 of 2,605 cSCC patients identified PNI (HR 1.61), involved margins (HR 2.34), and immunosuppression (HR 3.02) as significant poor prognostic factors—but notably, size and depth alone without these features did not mandate adjuvant therapy

• 2026 NCDB analysis 4 demonstrated that PNI-positive patients who received RT had outcomes comparable to PNI-negative patients, while PNI-positive patients without RT had worse survival—suggesting RT specifically addresses the PNI risk, not size/depth alone

European Consensus Position

The 2015 European consensus guideline 5 recommends:

• 5 mm margins for low-risk tumors
• 10 mm margins for tumors >6 mm thickness OR with high-risk features (high grade, perineural invasion, recurrent tumors)
• Adjuvant RT is reserved for positive margins, substantial PNI, or inoperable disease

Clinical Algorithm for Your Case

Given:

• Size: >2 cm ✓ (concerning)
• Depth: 4 mm (moderate, <6 mm threshold)
• LVI: Negative ✓ (favorable)
• PNI: Negative ✓ (favorable)
• Location: Auricular (manageable with surgery)

Decision pathway:

1. Confirm complete excision with adequate margins (≥5 mm, preferably 10 mm given size)
2. If margins are clear: Observation with close surveillance
3. If margins are close (<5 mm) or positive: Re-excision preferred over RT
4. Only consider adjuvant RT if:
   • Margins remain positive after optimal re-excision attempts
   • Patient is not a surgical candidate for re-excision
   • Immunosuppression is present (increases risk 2-3 fold)

Surveillance Strategy

Given the >2 cm size, implement:

• First 2 years: Every 3-4 months (70-80% of recurrences occur within 2 years 6)
• Years 3-5: Every 6 months
• Beyond 5 years: Annual examinations
• Patient education on self-examination and sun protection
• Regional lymph node examination at each visit

Common Pitfalls to Avoid

1. Don't reflexively radiate based on size/depth alone when pathologic high-risk features are absent—this exposes patients to unnecessary morbidity (lymphedema, tissue fibrosis)

2. Don't confuse "substantial" PNI with incidental microscopic involvement—only extensive neurotrophism or large nerve involvement warrants adjuvant RT 6

3. Don't use outdated 3 cm radiation depth—if RT is ultimately needed, use CT-based planning to ensure adequate nodal coverage 7

4. Ensure immunosuppression status is documented—this triples metastatic risk and may lower threshold for adjuvant therapy 3

The absence of LVI and PNI in your case is the decisive factor that argues against adjuvant radiotherapy, despite the concerning size and moderate depth. Complete surgical excision with adequate margins followed by surveillance is the evidence-based approach 1, 5.