MATERIALS AND METHODS: MEDLINE was systematically searched using prespecified criteria. Publications (previous 10 years) that reported tumour characteristics, treatment patterns, survival outcomes, and/or safety outcomes of patients with soft-tissue sarcoma were selected. Exclusion criteria were studies of patients <18 years of age; ≤ 10 patients; countries other than Australia, Hong Kong, Indonesia, Korea, Malaysia, New Zealand, Philippines, Singapore, Taiwan, or Thailand; >20% benign tumours; sarcomas located in bones or joints; gastrointestinal stromal tumour; Kaposi's sarcoma; or not reporting relevant outcomes.

RESULTS: Of the 1,822 publications retrieved, 35 (32 studies) were included. Nearly all patients (98%, 1,992/2,024; 31 studies) were treated with surgery, and more studies used adjuvant radiotherapy than chemotherapy (24 vs 17 studies). Survival outcomes and recurrence rates varied among the studies because of the different histotypes, sites, and disease stages assessed. Only 5 studies reported safety findings.

METHODS: We did a genome-wide association study of 189 patients with extranodal NKTCL, nasal type (WHO classification criteria; cases) and 957 controls from Guangdong province, southern China. We validated our findings in four independent case-control series, including 75 cases from Guangdong province and 296 controls from Hong Kong, 65 cases and 983 controls from Guangdong province, 125 cases and 1110 controls from Beijing (northern China), and 60 cases and 2476 controls from Singapore. We used imputation and conditional logistic regression analyses to fine-map the associations. We also did a meta-analysis of the replication series and of the entire dataset.

FINDINGS: Associations exceeding the genome-wide significance threshold (p<5 × 10(-8)) were seen at 51 single-nucleotide polymorphisms (SNPs) mapping to the class II MHC region on chromosome 6, with rs9277378 (located in HLA-DPB1) having the strongest association with NKTCL susceptibility (p=4·21 × 10(-19), odds ratio [OR] 1·84 [95% CI 1·61-2·11] in meta-analysis of entire dataset). Imputation-based fine-mapping across the class II MHC region suggests that four aminoacid residues (Gly84-Gly85-Pro86-Met87) in near-complete linkage disequilibrium at the edge of the peptide-binding groove of HLA-DPB1 could account for most of the association between the rs9277378*A risk allele and NKTCL susceptibility (OR 2·38, p value for haplotype 2·32 × 10(-14)). This association is distinct from MHC associations with Epstein-Barr virus infection.

INTERPRETATION: To our knowledge, this is the first time that a genetic variant conferring an NKTCL risk is noted at genome-wide significance. This finding underlines the importance of HLA-DP antigen presentation in the pathogenesis of NKTCL.