What is the treatment for Merkel cell carcinoma?

Treatment of Merkel Cell Carcinoma

For localized Merkel cell carcinoma, perform wide local excision with 1-2 cm margins to fascia, coordinate sentinel lymph node biopsy, and initiate adjuvant radiation therapy expeditiously; for metastatic disease, use immune checkpoint inhibitors (avelumab or pembrolizumab) as first-line therapy. 1

Initial Diagnostic Approach

• Begin with excisional biopsy using narrow margins to obtain accurate diagnostic and microstaging information 1
• Coordinate sentinel lymph node biopsy (SLNB) before or concurrent with definitive wide local excision to maximize staging accuracy 1
• Obtain imaging (CT, MRI, or PET/CT) if regional lymph nodes are involved to exclude distant metastasis 1

Localized Disease Management

Surgical Excision

• Achieve 1-2 cm lateral margins extending to investing fascia or pericranium when clinically feasible 1, 2
• For facial or cosmetically sensitive areas, consider Mohs micrographic surgery or complete circumferential peripheral and deep-margin assessment (CCPDMA) for tissue sparing 2
• Delay extensive reconstruction until negative margins are confirmed histologically to avoid obscuring margins and delaying adjuvant radiation 1, 2
• Use primary closure when possible to minimize delay to adjuvant radiation 2

Sentinel Lymph Node Biopsy Results Guide Regional Management

• Negative SLNB: Deliver radiation to primary site only 1
• Positive SLNB (microscopic disease): Deliver 50 Gy to the nodal basin in addition to primary site radiation 1

Adjuvant Radiation Therapy

• Critical timing: Initiate radiation therapy expeditiously after surgery, as delay worsens outcomes 1
• Primary site dosing: Deliver 50-56 Gy for negative margins 1
• Minimize tissue movement during reconstruction that could delay or complicate radiation planning 1, 2

Regional Disease (Clinically Positive Lymph Nodes)

• Confirm diagnosis with fine-needle aspiration or core biopsy with appropriate immunopanel 1
• Obtain imaging to exclude distant metastasis 1
• Perform lymph node dissection with or without radiation therapy if no distant metastasis is found 1

Metastatic/Advanced Disease

First-Line Therapy

• Use immune checkpoint inhibitors (avelumab or pembrolizumab) as first-line therapy for advanced/metastatic Merkel cell carcinoma 1
• These agents demonstrate objective response rates exceeding 50% with durable responses 3

Alternative Systemic Therapy

• For patients requiring debulking or unable to tolerate immunotherapy, use cisplatin or carboplatin with or without etoposide 1
• Note that chemotherapy responses are typically short-duration (approximately 3 months) with unclear overall survival benefit 4, 5

Surveillance After Treatment

• Perform complete skin and regional lymph node examination every 3-6 months for the first 2 years 1
• After 2 years, decrease frequency to every 6-12 months 1
• Critical timing consideration: 90% of recurrences occur within 24 months, with median time to recurrence of 8 months 1
• Blood-based surveillance tests (Merkel cell polyomavirus antibodies and circulating tumor DNA) are available with excellent sensitivity 3

Key Clinical Pitfalls

• Avoid delaying adjuvant radiation therapy: Expeditious initiation is critical for outcomes 1
• Do not perform extensive reconstruction before confirming negative margins: This can obscure histologic assessment and delay radiation 1, 2
• Recognize that pre-radiation margin status had no impact on locoregional failure in patients receiving adjuvant radiation therapy, so tissue-sparing approaches with adjuvant RT are reasonable 2
• Be aware that MCC is highly aggressive with a 40% recurrence rate, necessitating close surveillance 3