Treatment with ipilimumab Table S1 Treatment with ipilimumab Responder Non-responder No. Patients 30 48 Number of received doses (ipilimumab 3 mg/kg) 4 doses 22 24 3 doses 4 5 2 doses 3 7 1 dose 6 Unknown 1 Table S1: Patients received ipilimumab 3 mg/kg within clinical trials and later on as approved therapy. From 78 treated patients 46 patients received four doses, nine patients received three doses, ten patients received two doses and 6 patients received one dose. For 7 patients the number of received doses is unknown. The number of infusions was similar in both groups. Patients did not receive all four doses due to side effects or progression of disease.

Figure S1: Pretreatment of patients in stage IV before administration of ipilimumab. More than 48% (38 out of 78 patients) received at least three prior treatment regimens before undergoing therapy with ipilimumab.

Specimen-Nr. Tumor content (% area) PD-L1 expression (40-delta CT) Expression classification (cut-off at CT 28,86) % tumor membrane expression of PD-L1 IHC classification (positive=>5% stained tumor cells IHC staining (P=Princeton clone 28-8; E=Erlangen, GTX117446) 1 40 29,93 PD-L1 low INDETERMINATE* NE P 2 73 24,98 negative 3 50 27,11 4 35 28,78 5 75 29,05 PD-L1 high 6 25 29,33 7 90 29,42 8 65 29,90 9 30,20 10 60 30,25 11 31,33 positive 12 98 31,41 13 20 32,04 14 95 27,90 E 15 27,80 16 28,60 17 29,10 18 19 85 30,78 31,01 21 31,05 22 31,11 23 31,16 24 31,20 31,25 26 27 70 31,30 28 31,31 29 30 31 31,53 32 31,54 33 80 31,68 34 31,70 36 32,17 37 100 32,74 38 55 32,76 * due to high melanin content Figure S2: Immunohistochemical staining of 38 specimen for PD-L1 expression. Specimen with > 5% membranous staining were categorized “positive”. Shaded in green: Concordance between RT-PCR and IHC. NE: Not evaluable due to too much melanin

Concordance between RT-PCR and immunohistochemistry PD-L1 antibody Positive concordance between RT-PCR and immunohistochemical staining No concordance between RT-PCR and immunohistochemical staining BMS/Dako antibody (Princeton) 36 % 64 % CD274 antibody (Erlangen) 80 % 20 % Figure S3: Correlation of expression data from RT-PCR with immunohistochemical staining of specimen for PD-L1 expression in 38 cases. The BMS/DAKO antibody (Princeton) did not deliver any result in 2 out of 13 cases due to too much melanin and concordance with RT-PCR classification in only 4/11 cases. The CD274 antibody (Erlangen) showed better correlation with the RT-PCR results with concordance in 20/25 cases.