The non-cancerous components in tumor tissues, e.g., infiltrating stromal cells and immune cells, dilute tumor purity and might confound genomic mutation profile analyses and the identification of pathological biomarkers. It is necessary to systematically evaluate the influence of tumor purity. Here, using public gastric cancer samples from The Cancer Genome Atlas (TCGA), we firstly showed that numbers of mutation, separately called by four algorithms, were significant positively correlated with tumor purities (all p < 0.05, Spearman rank correlation). Similar results were also observed in other nine cancers from TCGA. Notably, the result was further confirmed by six in-house samples from two gastric cancer patients and five in-house samples from two colorectal cancer patients with different tumor purities. Furthermore, the metastasis mechanism of gastric cancer may be incorrectly characterized as numbers of mutation and tumor purities of 248 lymph node metastatic (N + M0) samples were both significantly lower than those of 121 non-metastatic (N0M0) samples (p < 0.05, Wilcoxon rank-sum test). Similar phenomena were also observed that tumor purities could confound the analysis of histological subtypes of cancer and the identification of microsatellite instability status (MSI) in both gastric and colon cancer. Finally, we suggested that the higher tumor purity, such as above 70%, rather than 60%, could be better to meet the requirement of mutation calling. In conclusion, the influence of tumor purity on the genomic mutation profile and pathological analyses should be fully considered in the further study.

肿瘤组织中的非癌性成分（例如，浸润的基质细胞和免疫细胞）稀释了肿瘤的纯度，并可能混淆基因组突变图谱分析和病理生物标记物的鉴定。有必要系统地评估肿瘤纯度的影响。在这里，我们使用来自癌症基因组图谱（TCGA）的公共胃癌样本，首先表明，突变的数量（分别由四种算法调用）与肿瘤的纯度显着正相关（所有p<0.05，斯皮尔曼等级相关性。在TCGA的其他9种癌症中也观察到了类似的结果。值得注意的是，该结果被来自两个胃癌患者的六个内部样本和来自两个具有不同肿瘤纯度的大肠癌患者的五个内部样本进一步证实。此外，胃癌的转移机制可能被错误地表征为248个淋巴结转移（N + M0）样本的突变数和肿瘤纯度均显着低于121个非转移（N0M0）样本（p<0.05，Wilcoxon秩和检验）。还观察到类似的现象，即肿瘤纯度可能混淆胃癌和结肠癌的癌症组织学亚型分析和微卫星不稳定性状态（MSI）的鉴定。最后，我们建议更高的肿瘤纯度，例如高于70％，而不是60％，可以更好地满足突变调用的要求。总之，在进一步研究中应充分考虑肿瘤纯度对基因组突变谱和病理分析的影响。