P45. The management of mucosal melanoma: a population-based analysis of treatment patterns and outcomes

Mucosal melanoma (MM) is a rare malignancy with complex anatomic and therapeutic considerations, and historically poor prognosis. Evidence is limited and most data predates the use of immunotherapy (IO) and targeted therapy (TT).  We describe temporal trends in MM incidence, treatment, and survival in a population-based cohort.


Methods:

Adults with MM were retrospectively identified through the Ontario Cancer Registry (2010-2022) and linked with administrative databases to capture disease features, treatment, overall (OS) and cancer-specific survival (CSS). Primary sites were anorectal (AR), gastrointestinal (GI), gynecologic (GYN), head and neck (HN) and urologic (URO). Descriptive, survival, and multivariate regression analyses (MVA) were performed to identify factors associated with OS and CSS.


Results:

We included 632 patients (median age 72y, 73% female). Annual standardized incidence rate (ASIR) was 0.30-0.54/100,000. Most common sites were GYN (37%, ASIR 0.15) and HN (33%, ASIR 0.13), followed by AR (18%, ASIR 0.07), GI (8%, ASIR 0.03) and URO (3%, ASIR 0.01).

Within 6 months of diagnosis, 95% of patients had surgical (SO), 60% radiation oncology (RO) and 54% medical oncology (MO) consultations (Table 1). MO consultations rose after 2017 (43 vs 65%, p< 0.001); RO and SO remained stable. Staging imaging was performed in 93% of patients: thorax CT (88%), abdominopelvic CT (87%) and brain imaging (40-44%). Stage was unrecorded in 80% of cases.

Surgery was completed in 363 (75%) cases, including primary tumor resection (74%) and lymph node biopsy/dissection (17%), with no site differences.

Chemotherapy (ChT) was given in 40% and was the most common systemic treatment within 1 year (68% adjuvant [ADJ], 6% neoadjuvant [NA]), followed by IO (33%, ADJ 65%, NA 6%) and TT (3%). Systemic therapy use increased after 2017 (ChT 30 vs 52%, IO 15 vs 52%, both p< 0.001), with no site differences. ADJ radiation was given in 25% cases, more often in HN (46%, p< 0.001), with no temporal change.

Five-year OS was 32% (95% CI 27-36), higher in GYN (39%) and URO (39%) and lower in AR (24%) and GI (23%)(p=0.01), with no improvement over time (2010-2016 29% vs 2017-2022 34%, p=0.3). Five-year CSS was 38% (95% CI 34-43), with no site-specific difference. On MVA, older age, AR, GI and H&N sites were associated with worse OS and CSS.


Conclusions:

MM requires complex multidisciplinary care. Despite increasing MO involvement and IO use, outcomes remain poor.  Strengthening cancer registries, early referral to cancer centers and inclusion in clinical trials are essential to improving care.