KEY POINTS
- The DEGRO Dermatooncology Working Group reviewed current international guidance and clinical evidence to provide practical recommendations for radiotherapy across stage I–IV Merkel cell carcinoma.
- For localized and regional disease, surgery followed by adjuvant irradiation of the tumor bed remains standard. DEGRO emphasizes starting postoperative radiotherapy within 8 weeks after surgery, because longer delays are associated with greater locoregional failure.
- Conventional postoperative treatment is generally around 50 Gy in 25–28 fractions. Alternative shortened schedules include 2.25–2.5 Gy ×20 or 3–4 Gy ×10, while 8 Gy ×1 may be considered only in carefully selected low-risk or frail patients.
- For definitive treatment, suggested shortened options include 3 Gy ×10–15, 4 Gy ×10, 6 Gy ×5–6 on non-consecutive days, and 8 Gy ×3 on non-consecutive days, alongside conventionally fractionated definitive regimens.
- Regional nodal irradiation is recommended for involved nodes and may be considered in selected pN0 patients with high-risk features or unreliable sentinel-node assessment. In clinically node-positive disease with multiple nodes or extranodal extension, nodal dissection followed by radiotherapy remains appropriate.
- For palliation, practical regimens include 30 Gy in 10 fractions, 20 Gy in 5 fractions, or 8 Gy in one fraction, with repeat treatment possible in selected situations.
- The recommendations also emphasize 3–5 cm CTV margins around the primary tumor bed where anatomically appropriate, use of bolus for adequate skin dose, and FDG-PET/CT because it can alter stage in approximately 30–40% of patients.
CLINICAL TAKEAWAY
The major shift is not away from postoperative radiotherapy, but toward greater flexibility in how it is delivered. Conventional treatment remains the reference for fit patients, while shorter schedules provide reasonable alternatives when age, frailty, comorbidity or treatment burden matter.