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- Presentation
Current Controversies in Merkel Cell Carcinoma: Surveillance with Blood-Based Assays and Adjuvant Radiation
Description
The talk focused on two current controversies in Merkel cell carcinoma (MCC): blood-based surveillance and adjuvant radiation dosing. The speaker emphasized that after diagnosing MCC, clinicians should perform a full skin and nodal exam, obtain a STAT PET-CT for staging, and refer urgently to the appropriate surgical, medical, and radiation oncology teams. For surveillance, two blood tests are available: AMERK, which detects antibodies to Merkel polyomavirus and works only in virus-positive patients, and circulating tumor DNA (ctDNA), which can be used regardless of viral status. The speaker described ctDNA as more specific and more useful overall than AMERK, with higher predictive value and similar or slightly better lead time; in a head-to-head comparison, ctDNA outperformed AMERK on multiple metrics, and the combination of both tests did not add benefit. Their current practice is to use AMERK initially to determine viral status, then rely on serial ctDNA after treatment when available, while continuing imaging for a period when ctDNA is not informative. The second controversy was how much adjuvant radiation to give. Radiation is effective in MCC because of the tumor’s rapid proliferation, but it carries meaningful toxicity, especially in the head and neck. Standard adjuvant doses have often been 50–60 Gy, largely borrowed from other cancers, but retrospective data suggest lower-dose regimens such as 8 Gy may be adequate in selected patients, particularly those with fewer risk factors, though the evidence is not yet definitive. A prospective randomized trial is being planned to better determine the optimal dose. The speaker concluded by encouraging community dermatologists to use these surveillance tools and reach out to MCC experts when needed.
View moreConclusions
- For Merkel cell carcinoma surveillance, circulating tumor DNA appears to outperform AMERK overall and is the preferred blood-based test because it applies to all patients, has higher positive predictive value, and performs at least as well on negative predictive value and lead time.
- AMERK remains useful mainly as an initial test to determine whether a patient is polyomavirus-positive, but it is less reliable after multiple recurrences and during immunotherapy.
- A practical surveillance strategy is to use ctDNA for ongoing follow-up, reserve AMERK selectively for virus-positive patients when ctDNA is negative, and continue imaging for a limited period when initial disease status is uncertain.
- Early diagnosis of Merkel cell carcinoma should be followed by a full skin and nodal exam plus a STAT PET-CT, because occult nodal or metastatic disease is common and changes management.
- Neoadjuvant immunotherapy can produce complete pathologic responses in advanced MCC, but immune-related adverse events may limit treatment duration.
- Radiation therapy is effective in MCC because the tumor is highly radiosensitive, and it can be used in adjuvant, definitive, or palliative settings with meaningful control benefits.
- Adjuvant radiation is generally recommended when one or more NCCN risk factors are present, especially larger tumors, head and neck primaries, lymphovascular invasion, immunosuppression, or positive margins.
- The traditional 50 to 60 Gy adjuvant dosing paradigm is largely borrowed from other cancers rather than being MCC-specific, and it may expose patients to substantial toxicity.
- Single-fraction 8 Gy radiation may be an effective lower-toxicity alternative for some resected MCC cases, especially when toxicity avoidance and convenience are priorities.
- Current retrospective data suggest 8 Gy can achieve promising local control in selected patients, but the evidence is not yet definitive because of selection bias and nonrandomized comparisons.
- Because the optimal adjuvant radiation dose remains uncertain, the field is moving toward a prospective randomized trial comparing observation, 8 Gy, and conventional 50 to 60 Gy regimens based on risk level.
- General dermatologists can and should play a central role in both staging and longitudinal surveillance of MCC, but complex cases should be referred promptly to specialty centers when needed.
- Rao’s dosing recommendations
- Rush et al.’s dosing recommendations
- Adjuvant single-fraction radiotherapy to the resected primary tumor site and stage IIIA regional disease results in high locoregional control in Merkel cell carcinoma in a single-institution retrospective study. Michael Dykstra, Cindy E Parra, James A Heyman, Kelly L Harms. J Am Acad Dermatol. 2025. PMID: 3998790. DOI: 10.1016/j.jaad.2025.01.099#10.1016/j.jaad.2025.01.099