Aims: To investigate patterns of recurrence in Merkel cell carcinoma (MCC) to guide future recommendations on surveillance imaging, especially in detecting early asymptomatic distant recurrence.
Methods: Review of a prospective database of 267 patients diagnosed with MCC between 1980-2019 at Westmead hospital, Sydney. All patients were treated with curative intent most often with a combination of surgery and radiotherapy. Data on patient demographics, clinical details, tumour characteristics was obtained including tumour size, location, recurrence and treatment. Descriptive analysis was performed using SPSS Statistics 25 software.
Results: One hundred and twenty-nine patients (48%) developed recurrence with a median duration from diagnosis to first recurrence of 7.6 months. The most frequent first site of recurrence was regional (42%), followed by distant (36%), local (16%), and locoregional (5%). The most common sites of distant recurrence were cutaneous (29%) and distant (non-regional) lymph nodes (27%). The liver was the most frequent site of visceral metastatic disease (20%), and brain and lung metastases were infrequent. Patients with unknown primary had the highest rate of developing distant relapse (69%) as the first site of recurrence followed by upper limb primaries (47%). 59% of immunocompromised patients developed relapse.
Conclusions: Following treatment MCC can metastasise to any site with certain sites having a greater predilection than others. PET scan imaging is considered best practice for detecting early asymptomatic recurrence. Higher risk patients, such as node positive or immunosuppressed patients, may benefit from more frequent regular follow imaging. The benefit of initiating systemic immunotherapy in asymptomatic patients with recurrence remains unknown but may improve outcome.