Real-world changes in the clinical management of resected stage III melanoma at high risk of local recurrence in the era of modern systemic therapies.

e21575 Background: Adjuvant systemic therapies (ST) for patients with resected stage III melanoma have improved relapse-free survival; however, the role of adjuvant radiotherapy (RT), previously the mainstay adjuvant treatment, is undefined in the modern ST era. Real-world data detailing clinical practice changes and its impact on outcomes are needed to help inform the choice of adjuvant therapy for patients with resected stage III melanoma. Methods: In this single-center retrospective study, patients from Princess Margaret Cancer Centre with resected stage III cutaneous melanoma treated between 2010 and 2019 and fitting the 2016 Cancer Care Ontario guidelines for adjuvant RT were included. Demographic, pathological, and clinical data were abstracted from electronic medical records. PFS was defined as the time from lymph node dissection to local-regional recurrence in the treated nodal basin or distant recurrence. OS was defined as time from lymph node dissection to death by any cause. The Log-rank method was applied to assess survival endpoints. A p-value < 0.05 was considered statistically significant. Results: From 4,959 records reviewed, 109 patients were identified. Median age at time of surgical resection was 59.4 years (23.6-89.8), and 74 (68%) were male. Type of adjuvant therapy and number of local-regional recurrences (LR) are expressed in the table. The median follow-up among those alive at last follow-up was 54.2 months (range 1.9-122). The proportion of patients receiving adjuvant RT was higher between 2010 and 2014 than it was between 2015 and 2019 (59% to 26%), whilst the proportion of those receiving adjuvant ST progressively grew (3% to 50%). LR > 90 days following lymph node dissection as the first site of relapse or synchronously with progression to metastatic disease was rare in patients treated with either adjuvant RT (6.8%) or adjuvant ST (14.3%, chi-square p = 0.33). Median progression free survival was 12.3 months in patients treated with adjuvant RT and 43.8 months in patients treated with adjuvant ST (p = 0.007). Overall survival was not significantly different (p = 0.08). Conclusions: The advent of ST has changed our institution’s clinical practice with ST replacing RT as the primary adjuvant treatment modality. Our data suggests that in the current adjuvant treatment landscape, omission of RT does not seem to increase rates of local-regional recurrences, and patients with resected stage III melanoma can be safely spared from adjuvant RT without detrimental effect on survival.[Table: see text]