Although metastases from original (primary) tumors are highly studied, metastases from metastatic sites (secondary tumors) are far less studied. Here, using data from metastasis map (MetMap) project reported in a recent study (Jin et al. in Nature 588(7837): 331–336. https://doi.org/10.1038/s41586-020-2969-2, 2020), we found that human cancer cell lines isolated from metastatic sites have higher potential to metastasize to another site in mice, compared to human cancer cell lines isolated from primary sites, for certain types of cancer including liver, lung and pancreas cancer. In contrast, for cancer types such as ovarian and skin cancer, human cancer cell lines originated from primary tumors have increased metastatic potential in mice, compared to human cancer cell lines originated from metastatic sites. This preliminary analysis points that the potential of metastases to further metastasize compared to that of primary tumors might be cancer type-dependent, and further research is needed to understand why certain cancer cell lines isolated from metastatic sites are more likely to spread to other organs.

尽管对原始（原发性）肿瘤的转移进行了高度研究，但对转移部位（继发性肿瘤）的转移研究却很少。在这里，使用最近一项研究报告的转移图（MetMap）项目的数据（Jin et al. in Nature 588(7837): 331–336. https://doi.org/10.1038/s41586-020-2969-2, 2020），我们发现，对于某些类型的癌症，包括肝癌、肺癌和胰腺癌，与从原发部位分离的人类癌细胞系相比，从转移部位分离的人类癌细胞系更有可能转移到小鼠的另一个部位。相比之下，对于卵巢癌和皮肤癌等癌症类型，与源自转移部位的人类癌细胞系相比，源自原发性肿瘤的人类癌细胞系在小鼠中具有更高的转移潜力。