In a patient with left auricular squamous cell carcinoma 2.5 cm in size, depth of invasion 5 mm, negative surgical margins, and no lymph‑vascular or perineural invasion, is adjuvant radiotherapy indicated and what dose should be prescribed?

Adjuvant Radiotherapy for Auricular SCC: Recommendation

Adjuvant radiotherapy is NOT indicated for this patient with left auricular squamous cell carcinoma given the favorable pathologic features: 2.5 cm size, 5 mm depth of invasion, negative margins, and absence of lymphovascular or perineural invasion.

Rationale Based on Evidence

Why Radiotherapy is Not Indicated

The most recent and relevant guideline evidence for cutaneous SCC management comes from the AAD Guidelines 1, which recommend adjuvant radiotherapy primarily for:

• Positive margins that cannot be cleared surgically
• Perineural invasion (PNI)
• High-risk features suggesting regional/distant metastasis risk

Your patient has none of these indications:

• Margins are negative (clear)
• No perineural invasion (PNI negative)
• No lymphovascular invasion (LVI negative)
• Tumor size 2.5 cm is moderate, not massive
• Depth of invasion 5 mm is not extreme

Supporting Meta-Analysis Data

The 2021 systematic review and meta-analysis 2 identified specific prognostic factors warranting adjuvant radiotherapy:

• Perineural invasion (HR 1.61)
• Involved surgical margins (HR 2.34)
• Immunosuppression (HR 3.02)

Your patient has clear margins and no PNI, which are the two modifiable risk factors where adjuvant radiotherapy demonstrates benefit. The meta-analysis showed adjuvant radiotherapy improved outcomes specifically in patients with these risk factors, not in their absence.

Anatomic Location Considerations

While auricular SCC can be aggressive 3, 4, the evidence for routine adjuvant radiotherapy in completely resected auricular tumors with negative margins is lacking. The temporal bone/external auditory canal literature 3 shows adjuvant radiotherapy benefits primarily in:

• Positive or close margins
• Advanced T-stage (T3-T4)
• Bone invasion

Your patient's tumor was confined to the auricle with negative margins and no bone involvement mentioned.

Critical Caveats

When to Reconsider This Decision

You should reassess the need for adjuvant therapy if:

1. Margin adequacy is questioned: If margins are <5 mm, multidisciplinary discussion is warranted 5, 6
2. Immunosuppression exists: Organ transplant recipients or chronic immunosuppression increases metastatic risk 2-3 fold 1, 2
3. Depth of invasion >10 mm: Some evidence suggests DOI >10 mm warrants consideration of adjuvant therapy 7
4. Multiple high-risk features: Combination of size >2 cm + DOI >5 mm + poorly differentiated histology may warrant discussion

What Constitutes "Negative Margins"

Ensure margins are truly adequate:

• Peripheral margins ≥4-6 mm are generally considered adequate for cutaneous SCC
• Deep margin adequacy depends on anatomic constraints
• If margins are 1-3 mm, this may be considered "close" rather than truly negative 5

Surveillance Strategy Instead

Given no indication for adjuvant therapy, implement rigorous surveillance:

• Physical examination every 3-6 months for 2 years, then every 6-12 months 8
• Include total body skin examination and regional lymph node palpation (preauricular, postauricular, cervical nodes)
• Imaging only if clinically indicated by symptoms or examination findings
• Patient education on self-examination and prompt reporting of new lesions or lymphadenopathy

Dose Recommendation IF Radiotherapy Were Indicated

Should circumstances change or additional risk factors emerge, the standard adjuvant dose would be:

• 60 Gy in 30 fractions (2 Gy/fraction) to the tumor bed for negative margins 9
• 60-66 Gy if margins become positive or PNI is identified on re-review 9

However, this patient does not meet criteria for adjuvant radiotherapy based on current pathologic findings.