224 - Event-Free Survival after Definitive Radiotherapy vs. Upfront Surgery for Axillary and Inguinal Nodal Merkel Cell Carcinoma: A Population-Based Retrospective Analysis
Presenter(s)
D. Stoker1, G. Adrian1, M. B. Pinkham1, W. Xu2, R. Calvisi3, T. Read3, C. Allan4, D. Youlden5, P. Woodrow5, and L. J. McDowell1; 1Department of Radiation Oncology, Princess Alexandra Hospital, Brisbane, QLD, Australia, 2Department of Medical Oncology, Princess Alexandra Hospital, Brisbane, QLD, Australia, 3Department of Plastic and Reconstructive Surgery, Princess Alexandra Hospital, Brisbane, QLD, Australia, 4Division of Surgery, Mater Hospital Brisbane, Brisbane, QLD, Australia, 5Cancer Alliance Queensland, Metro South Health, Brisbane, QLD, Australia
Purpose/Objective(s):
Merkel cell carcinoma (MCC) is a rare and aggressive neuroendocrine cutaneous malignancy with predilection for regional lymph node metastases. The optimal management of regional disease remains uncertain. The purpose of this report was to compare outcomes between definitive radiation therapy (RT) and upfront surgical management in patients with nodal MCC.
Materials/Methods:
A retrospective cohort study was undertaken using the Queensland Oncology Repository, a population-based resource collating demographic, clinicopathological, treatment and outcome data for all cancer patients. The QOR was used to identify all patients diagnosed with AJCC Stage III MCC of the groin and axilla between 2012 and 2021. The primary outcome was event-free survival (EFS), comparing definitive RT to primary surgical management (with or without adjuvant treatment) using Kaplan-Meier estimates and multivariable Cox-Regression. Secondary endpoints included regional relapse, distant progression, and overall survival (OS).
Results:
In total, 103/191 patients with axilla (57, 55%) or inguinal (46, 45%) nodal disease were treated with curative intent. The majority were older males (male 73/103, 71%; median age 72; IQR 65 - 79). Most patients had clinically positive disease (85/103, 83%), while a minority had microscopic disease detected via sentinel lymph node biopsy (18/103, 17%).
Definitive treatment was non-surgical in 56/103 patients (54%), with either RT alone (42, 75%) or CRT (14, 25%). Lymph node dissection was the primary treatment in 47/103 (46%) patients, with 32/47 (65%) who went on to receive adjuvant treatment: either RT alone (22, 47%), chemoradiation (8, 17%) or chemotherapy alone (2, 4%).
At a median follow-up of 40 months, two-year EFS was similar between definitive RT/CRT (52%, 95% CI 40-66%) versus upfront surgery (49%, 95% CI 37-66%; HR 1.04, 95% CI 0.69-1.76, p=0.868). Two-year OS was also similar at 66% (95% CI 56-83%) for the RT/CRT group and 68% (95% CI 56-83%) for the surgical group (HR 1.37, 95% CI 0.84-2.24, p=0.205).
At 2 years, regional failure was infrequent and similar between groups (RT/CRT vs surgery, 4%, 95% CI 0-10%; vs 7%, 95% CI 0-15%). However, the two-year rate of distant failure was substantial in both arms, 31% (95% CI 17–42%) with RT/CRT versus 36% (95% CI 20–59%) with surgery. The cumulative incidence of distant metastases at five years continued to increase, reaching 47% (95% CI, 30–61%) and 46% (95% CI, 27–60%) in the radiotherapy and surgery arms, respectively.
Conclusion:
Regional control and event-free survival were similar following definitive RT/CRT versus upfront surgery of axillary and inguinal MCC. The high rate of distant metastases highlights systemic therapy as a key clinical priority.