e21052 Background: Non immediate allergic reactions (niAR) related with oncology drugs are a rare entity. Usually, it is called Drug Reaction with eosinophilia and sistemic symptoms (“DRESS”), occurring at first ten days of treatment.Recently, the treatment of metastatic melanoma (MM) has included new drugs in patients wtih BRAF V600E mutation. Despite skin reactions are usual, niAR to these drugs have not been reported. We present 2 clinical cases with mm treated with BRAFi, developing such niAR. Methods: Patient 1: 47yo female with lymph node relapse and multiple subcutaneous skin metastases (previously pT1N0M0 melanoma) that received nivolumab in adjuvant setting. BRAF-mutated. She starts with Vemurafenib-Cobimetinib (V-C). At 8 days, niAR (maculo-papular exantema G4, fever G2). After discontinuation of this treatment (3 weeks), it is changed to Dabrafenib(50%)-Trametinib (D-T). With only 1 dose, skin niAR (G3) is newly developed. Biopsy are taken at the beginning (T0), during (T1) and after desentizitation (T2). Patient 2: 60 yo female, lung and lymph node relapse of melanoma (previously pT2bN0M0) after IFN-alpha adjuvant 2 years before. BRAF-mutated. Start with V-C. At 9 days, skin niAR (G4), with fever (G1). Discontinuation of treatment. Biopsys and blood test are taken (T0, T1 and T2). Gene expression was performed with PanCancer Immune Profiling Panel Nanostring™ in this points. Results: Different lymphocytic subpopulations in blood and biopsy at acute phase are showed in table 1. Immune gene expression profiling found decreased expression of 5 genes: UBC, IL8, IL32, NFKB1A and FOS, increasing IFNGR1 (pt 1). In both of pts, desensitizitation protocol by Allergologists was made succesfully, with incremental oncology drugs and steroid reduction protocol. Both of pts had a maior partial response (RECIST), even the scarce of the drug received. Conclusions: D and V develop important “of class” skin niAR. Different immunologic patterns are related with this niAR. Previous exposition to IFN or anti-PD1 therapy might modulate such response. Immune gene expression profiling could be used as a method to identify biomarkers. Desensitization with BRAFi has enough efficacy and tolerance.