e21532 Background: Atypical melanomas, such as acral lentiginous, uveal, mucosal, spitzoid, desmoplastic, meningeal, and primary occult site, represent less than 5% of melanoma cases. Due to their different biological tumor behavior from cutaneous melanomas, their treatment is still challenging. Currently, checkpoint inhibitors are the main treatment based on extrapolations or data from small surveys. Methods: This study aims to describe the epidemiological profile, clinical and pathological characteristics, and treatment of patients with atypical melanomas treated with immunotherapy. It is an observational, descriptive, retrospective study that analyzed 72 medical records of patients with atypical melanomas, ECOG 0-1, > 18 years old, treated with immunotherapy (neo, adjuvant, and palliative lines), between January 2015 and December 2023 at the A.C. Camargo Cancer Center, São Paulo, Brazil. Results: We gathered 72 patients, 61% male and 39% female, with an average age of 58.89 (±13.63) years; 57% were white, 15% African-descendant (black and brown), 8% Asian, and 20% not specified. Regarding primary site, 26% were acral, 24% mucosal, 24% occult primary site, 15% uveal, 8% desmoplastic, 1% amelanocytic, 1% spitzoid, and 1% cauda equina meningeal. Regarding staging, (3%) were stage I, (15%) stage II, (25%) stage III, (47%) stage IV, and (10%) unknown. LDH: 372.5 (±360) mg/dL. Metastases: lymph node 29%; hepatic 23%; pulmonary 21%; bone 18%; central nervous system 15%; peritoneal carcinomatosis 5%; stomach 3%; cauda equina 3%; adrenal 1%; in transit 1%; intestine 1%; bone marrow 1%; parotid 1%. BRAF mutations were present in 23% of cases (variants V660E, V600K, V660R, and G469R); NRAS 6% (codons 13 and 61); KIT 1% (exon 11) and NTRAK 1% (S701F). In relation to treatment, 5 received neoadjuvant anti-pd1 + anti-ctla4 combination, 13 adjuvant with anti-pd1+/- anti-ctla4. About 50 patients received systemic treatment for metastatic disease anti-pd1+/- anti-ctla4. Overall survival: 26 (±14.8) months. Conclusions: Atypical melanoma primary occult site is the most prevalent, with the majority diagnosed at stage IV, with high LDH levels and lymph nodes as the main sites of metastases. Twenty-three percent had a BRAF gene mutation. The majority were treated palliatively with first-line immunotherapy, with median survivals of 14.8 months.