The earliest events during human tumour initiation, although poorly characterized, may hold clues to malignancy detection and prevention¹. Here we model occult preneoplasia by biallelic inactivation of TP53, a common early event in gastric cancer, in human gastric organoids. Causal relationships between this initiating genetic lesion and resulting phenotypes were established using experimental evolution in multiple clonally derived cultures over 2 years. TP53 loss elicited progressive aneuploidy, including copy number alterations and structural variants prevalent in gastric cancers, with evident preferred orders. Longitudinal single-cell sequencing of TP53-deficient gastric organoids similarly indicates progression towards malignant transcriptional programmes. Moreover, high-throughput lineage tracing with expressed cellular barcodes demonstrates reproducible dynamics whereby initially rare subclones with shared transcriptional programmes repeatedly attain clonal dominance. This powerful platform for experimental evolution exposes stringent selection, clonal interference and a marked degree of phenotypic convergence in premalignant epithelial organoids. These data imply predictability in the earliest stages of tumorigenesis and show evolutionary constraints and barriers to malignant transformation, with implications for earlier detection and interception of aggressive, genome-instable tumours.

人类肿瘤发生过程中的最早事件虽然特征不明确，但可能为恶性肿瘤的检测和预防提供线索¹。在这里，我们通过人胃类器官中TP53的双等位基因失活（胃癌的常见早期事件）来模拟隐匿性肿瘤前期。通过两年多的多个克隆衍生培养物中的实验进化，建立了这种起始遗传损伤与所产生的表型之间的因果关系。TP53缺失引发进行性非整倍性，包括胃癌中普遍存在的拷贝数改变和结构变异，并具有明显的优先顺序。TP53-的纵向单细胞测序胃类器官缺陷同样表明恶性转录程序的进展。此外，用表达的细胞条形码进行的高通量谱系追踪显示了可重复的动态，最初具有共享转录程序的罕见亚克隆反复获得克隆优势。这个强大的实验进化平台揭示了癌前上皮类器官的严格选择、克隆干扰和显着程度的表型趋同。这些数据意味着肿瘤发生最早阶段的可预测性，并显示了恶性转化的进化限制和障碍，对于早期检测和拦截侵袭性、基因组不稳定的肿瘤具有重要意义。