In a patient with a 2.5 cm cutaneous squamous‑cell carcinoma of the left auricle, depth of invasion 4 mm, negative surgical margins but with lymph‑vascular invasion and perineural invasion, is adjuvant radiotherapy indicated and what radiation dose should be prescribed?

Adjuvant Radiotherapy for Cutaneous SCC of the Auricle with LVI and PNI

Yes, adjuvant radiotherapy is indicated for this patient despite negative margins, given the presence of both lymphovascular invasion (LVI) and perineural invasion (PNI), which are established high-risk features that significantly increase locoregional recurrence risk. The recommended dose is 60 Gy in 2 Gy fractions to the tumor bed and at-risk nodal regions.

Rationale for Adjuvant Radiotherapy

High-Risk Features Present

Your patient has multiple concerning pathologic features:

• Perineural invasion (PNI): This is one of the most important adverse prognostic factors in cutaneous SCC, associated with significantly increased risk of locoregional recurrence (HR 1.61) 1
• Lymphovascular invasion (LVI): Another intermediate-to-high risk factor that independently predicts worse outcomes
• Auricular location: The ear is a high-risk anatomic site with increased metastatic potential
• Tumor size 2.5 cm: Meets threshold for higher-risk disease
• Depth of invasion 4 mm: Substantial depth indicating aggressive biology

Evidence Supporting Adjuvant RT

The most recent meta-analysis demonstrates that adjuvant radiotherapy significantly improves outcomes in high-risk cutaneous SCC, with lower recurrence rates (OR 0.56), longer disease-free survival (OR 2.17), and improved overall survival (OR 2.94, HR 0.47) 1. Critically, PNI was identified as a significant prognostic factor for poor outcomes (HR 1.61), and adjuvant radiotherapy was beneficial irrespective of surgical margin status when risk factors like PNI are present 1.

Real-world data from Merkel cell carcinoma guidelines (which share similar high-risk features with aggressive cutaneous SCC) support adjuvant RT for tumors with LVI even when margins are negative, particularly when the location can be easily incorporated into the radiation field 2.

Radiation Dose Recommendations

Standard Dosing for Negative Margins with High-Risk Features

Deliver 60 Gy in 2 Gy fractions once daily to the tumor bed and at-risk regional nodal basins 3. This is the established dose for postoperative radiotherapy in the absence of positive margins but with intermediate-to-high risk pathologic features.

Treatment Volume

Include:

• Primary tumor bed with adequate margin (typically 1-2 cm)
• Ipsilateral parotid region: Given auricular location and presence of PNI/LVI, there is 37.5% risk of occult parotid involvement in auricular SCC ≥2 cm, particularly with vascular involvement and PNI 4
• Level I-III cervical nodes: Consider elective nodal irradiation given high-risk features

The recent expert consensus emphasizes that incidental PNI with parotid proximity warrants extension of treatment volumes beyond the surgical bed alone 5.

Alternative Consideration

If there were positive margins (which you don't have), the dose would escalate to 60-66 Gy 3. Some practitioners might consider the higher end of this range (63-66 Gy) given the combination of both LVI and PNI, though 60 Gy is standard for your scenario.

Critical Clinical Pearls

Timing Matters

• Begin radiotherapy within 6 weeks of surgery, ideally keeping total time from surgery to completion of RT under 85 days 3, 6
• Delays beyond this timeframe significantly compromise outcomes

No Concurrent Chemotherapy Needed

For intermediate-risk factors like LVI/PNI without extracapsular extension or positive margins, concurrent systemic therapy is NOT routinely recommended 3. The evidence is insufficient and toxicity would be increased without proven benefit.

Surveillance Strategy

Given the high-risk features, implement aggressive follow-up:

• Clinical examination every 3 months for first 2 years
• Imaging (CT or MRI) of the head/neck at baseline and as clinically indicated
• Patient education about symptoms of perineural spread (facial pain, numbness, weakness)

Common Pitfalls to Avoid

1. Don't skip RT based solely on negative margins: The presence of PNI and LVI overrides margin status for treatment decisions 1

2. Don't underestimate auricular location: This is a high-risk site with documented increased metastatic potential, particularly to parotid nodes 4, 7

3. Don't use inadequate doses: 50-54 Gy is insufficient for high-risk features; 60 Gy is the minimum standard 3, 6

4. Don't omit parotid coverage: With PNI/LVI in auricular SCC, occult parotid involvement risk is substantial 4

Strength of Evidence

While the oropharyngeal SCC guidelines 3 provide the framework for adjuvant RT dosing (conditional recommendation, low-quality evidence for LVI/PNI alone), the 2021 meta-analysis 1 provides the strongest recent evidence specifically for cutaneous SCC, demonstrating clear survival benefits with adjuvant RT in the presence of PNI. The 2018 AAD guidelines 8 support adjuvant RT for high-risk features including PNI, though acknowledge limited high-level evidence.

The convergence of multiple guidelines and the recent meta-analysis strongly supports adjuvant RT at 60 Gy for your patient's presentation.