K. L. Ma1, C. E. Sharon1, G. N. Tortorello1, N. J. Perry2, E. H. Li2, J. N. Lukens3, G. C. Karakousis1, J. T. Miura1 1Hospital Of The University Of Pennsylvania, Department Of Surgery, Division Of Endocrine And Oncologic Surgery, Philadelphia, PA, USA 2University Of Pennsylvania, Perelman School Of Medicine, Philadelphia, PA, USA 3Hospital Of The University Of Pennsylvania, Department Of Radiation Oncology, Philadelphia, PA, USA
Introduction:
Merkel cell carcinoma (MCC) is a rare and aggressive skin cancer with high radiosensitivity. Historically, management of nodal micrometastases found on sentinel lymph node biopsy (SLNB) consisted of completion lymph node dissection (cLND). However, radiotherapy (RT) to the regional nodal basin without cLND may yield equivalent regional control. We sought to investigate practice patterns over time and outcomes of RT compared to cLND in the setting of MCC nodal micrometastasis found on SLNB.
Methods:
Patients with AJCC 8th edition pathologic stage IIIA MCC who received either lymph node basin RT or cLND (but not both) were identified from the National Cancer Database (2013-2018). RT was compared to cLND using multivariate logistic regression. Overall survival (OS) was assessed using Kaplan-Meier and Cox proportional hazards modeling. OS was further compared between RT and cLND groups following propensity score matching.
Results:
Of the 418 patients identified, the median age was 74 (interquartile range [IQR], 67-81), 66% (n=274) were men, and nearly all were white (97%, n=405). The majority (78%, n=326) of patients received cLND while 22% (n=92) received RT. There were no differences between the RT and cLND cohorts with regards to age (median, 75 vs. 74 respectively; p=0.42), sex (male, 67% vs 65%; p=0.67), tumor size (mm, 15 vs. 18; p=0.10), or comorbidity status (mean Charlson-Deyo score, 0.45 vs. 0.44; p=0.92). Patients who were diagnosed in a later year were more likely to receive RT (adjusted odds ratio by year, 1.37; 95% confidence interval [CI], 1.17-1.59; p=0.001), with a 3.98 average annual percentage point increase in the proportion of patients receiving RT. From 2016 to 2018, RT usage increased by 20.7 percentage points from 14.3% (n=8/56) to 35.0% (n=49/140) of patients. With a median follow-up time of 32 months (IQR, 19-54), there was no significant difference in overall survival (OS) between the RT and cLND cohorts (3-year survival, 66% vs. 62%; p=0.68). On Cox analysis, treatment modality (RT vs. cLND) was not associated with OS (p=0.49). After propensity score matching based on patient and tumor factors (n=81 for each cohort), treatment modality continued to have no significant impact on OS (3-year survival, RT 65% vs cLND 52%; p=0.09).
Conclusion:
For patients with nodal micrometastases from MCC, therapeutic radiation to the lymph node basin has increased in usage over the past several years, particularly since the reporting of data from the second Multicenter Selective Lymphadenectomy Trial (MSLT-II) for melanoma. Radiation is associated with similar overall survival outcomes compared to cLND, suggesting it is a safe alternative. Further study into patterns of recurrence for these treatments is needed.
