Adjunctive Radiation Therapy for Squamous Cell Carcinoma with Perineural Invasion
Recommendation
Adjuvant radiation therapy should be administered for squamous cell carcinoma on the scalp with focal perineural invasion following surgical resection to reduce the risk of recurrence and improve survival outcomes. 1
Treatment Algorithm
Primary Treatment
Surgical Excision
Adjuvant Radiation Therapy
Radiation Therapy Details
- Standard dose: 66 Gy (2 Gy/fraction) for areas with perineural invasion 1
- Treatment volume: Include the tumor bed and involved nerve pathways 3
- Technique: Consider intensity-modulated radiation therapy (IMRT) to minimize toxicity to surrounding tissues 2, 4
Evidence Supporting Recommendation
Perineural invasion (PNI) in cutaneous squamous cell carcinoma (cSCC) is a significant adverse prognostic factor that increases the risk of recurrence and metastasis. The ASTRO and ASCO guidelines strongly recommend adjuvant radiation therapy for cSCC with perineural invasion 1.
The American Academy of Dermatology guidelines state that "primary cSCC with concerning perineural invasion or otherwise at high risk for regional or distant metastasis may be considered for adjuvant radiation therapy to the local tumor site following surgical treatment" 1. This is particularly important for scalp lesions due to their proximity to critical neural structures.
Recent evidence from a 2023 study showed high local control rates (75%) in patients with high-risk PNI treated with adjuvant radiation therapy, including treatment of both involved and uninvolved, communicating cranial nerves 3. This study demonstrated few failures in electively treated regions, supporting the use of comprehensive radiation fields.
Special Considerations
Radiation Field Planning
- For focal (microscopic) perineural invasion, include the tumor bed and immediate surrounding area 3
- For more extensive perineural involvement, consider treating the entire course of the affected nerve to its origin 3
- MRI should be considered if large-nerve invasion is suspected, especially for tumors on the head and neck 1
Timing of Radiation
- The time from surgery to completion of radiotherapy should be kept as short as possible, ideally < 85 days 1
- Delaying radiation therapy beyond this window may compromise outcomes 1, 2
Potential Side Effects
- Radiation to the scalp may cause temporary or permanent alopecia
- Other potential side effects include skin erythema, desquamation, and fatigue
- Long-term risks include fibrosis and telangiectasia 1
Alternative Approaches
For patients who are not candidates for radiation therapy:
- Consider more extensive surgical resection if feasible
- Systemic therapy options may be considered for high-risk cases, though evidence is limited 1
- Close surveillance with more frequent follow-up is essential if adjuvant therapy is declined
Follow-up Recommendations
- Physical examination every 3-6 months for the first 2 years
- Radiologic imaging (CT or MRI) as clinically indicated
- Evaluation of thyroid function at 1,2, and 5 years if radiation was delivered to the neck 1, 2
Pitfalls and Caveats
Underestimating PNI: Even focal perineural invasion significantly increases recurrence risk and should prompt consideration of adjuvant radiation 5, 6
Delayed Treatment: Prolonged intervals between surgery and radiation completion (>85 days) may compromise outcomes 1
Inadequate Radiation Fields: Failure to include the full course of potentially affected nerves may lead to recurrence along neural pathways 3
Overlooking Other Risk Factors: Consider additional high-risk features (poor differentiation, depth >6mm, size >2cm) when determining the need for adjuvant therapy 1
Adjuvant radiation therapy represents a critical component in the management of cutaneous squamous cell carcinoma with perineural invasion, offering improved local control and potentially better survival outcomes compared to surgery alone.