KRAS, an oncogene, is frequently activated by mutations in many cancers. Kras-driven adenocarcinoma development in the lung, pancreas, and biliary tract has been extensively studied using gene targeting in mice. By taking the organoid- and allograft-based genetic approach to these organs, essentially the same results as in vivo models were obtained in terms of tumor development. To verify the applicability of this approach to other organs, we investigated whether the combination of Kras activation and Pten inactivation, which gives rise to endometrial tumors in mice, could transform murine endometrial organoids in the subcutis of immunodeficient mice. We found that in Kras^G12D-expressing endometrial organoids, Pten knockdown did not confer tumorigenicity, but Cdkn2a knockdown or Trp53 deletion led to the development of carcinosarcoma (CS), a rare, aggressive tumor comprising both carcinoma and sarcoma. Although they originated from epithelial cells, some CS cells expressed both epithelial and mesenchymal markers. Upon inoculation in immunodeficient mice, tumor-derived round organoids developed carcinoma or CS, whereas spindle-shaped organoids formed monophasic sarcoma only, suggesting an irreversible epithelial-mesenchymal transition during the transformation of endometrial cells and progression. As commonly observed in mutant Kras-driven tumors, the deletion of the wild-type Kras allele was identified in most induced tumors, whereas some epithelial cells in CS-derived organoids were unexpectedly negative for Kras^G12D. Collectively, we showed that the oncogenic potential of Kras^G12D and the histological features of derived tumors are context-dependent and varies according to the organ type and experimental settings. Our findings provide novel insights into the mechanisms underlying tissue-specific Kras-driven tumorigenesis.

KRAS是一种癌基因，在许多癌症中经常被突变激活。Kras驱动的肺、胰腺和胆道腺癌的发展已在小鼠中使用基因靶向进行了广泛的研究。通过对这些器官采用基于类器官和同种异体移植的遗传方法，在肿瘤发展方面获得了与体内模型基本相同的结果。为了验证这种方法对其他器官的适用性，我们研究了导致小鼠子宫内膜肿瘤的Kras激活和Pten失活的组合是否可以转化免疫缺陷小鼠皮下组织中的小鼠子宫内膜类器官。我们发现，在表达Kras ^G12D的子宫内膜类器官中，Pten敲低不会赋予致瘤性，但Cdkn2a敲低或Trp53缺失会导致癌肉瘤 (CS) 的发展，这是一种罕见的侵袭性肿瘤，包括癌和肉瘤。虽然它们起源于上皮细胞，但一些 CS 细胞同时表达上皮和间质标记。在免疫缺陷小鼠中接种后，肿瘤来源的圆形类器官发展为癌或CS，而纺锤形类器官仅形成单相肉瘤，这表明子宫内膜细胞的转化和进展过程中存在不可逆的上皮间质转变。正如在突变型Kras驱动的肿瘤中常见的那样，在大多数诱导肿瘤中都发现了野生型Kras等位基因的缺失，而 CS 衍生的类器官中的一些上皮细胞却意外地呈Kras ^G12D阴性。总的来说，我们表明Kras ^G12D的致癌潜力和衍生肿瘤的组织学特征是上下文相关的，并且根据器官类型和实验设置而变化。我们的研究结果为组织特异性Kras驱动的肿瘤发生机制提供了新的见解。