Background and purpose: Aneuploidy is associated with tumor formation. This study aimed to study the relationship between aneuploidy and tumorigenicity of tumor cells. Methods: The proliferations of C3 and C5 cell lines were tested by CCK-8 assay. Regular chromosome assay was used to analyze the karyotypes of the 2 cell lines. The tumorigenicity of C3 and C5 cell lines was tested by soft agar colony formation assay in vitro. The invasion and metastasis of C3 and C5 cell lines were detected by transwell chamber. The tumorigenicity of C3 and C5 cell lines was tested by xenograft in vivo. Results: The proliferative ability of C3 was stronger than that of C5. The difference was statistically significant. The karyotype assay showed that the karyptypes of the C3 and C5 cell lines were all aneuploid and their model numbers were 38-78 for C3 cell line and 28-50 for C5 cell line respectively. The proportions of C3 hypodiploid

diploid and hyperdiploid were 20.33%

8.47%

and 71.2%

respectively. The proportions of C5 hypodiploid

diploid and hyperdiploid were 11.11%

86.42%

and 2.47 %

respectively. The proportions of aneuploid C3 and C5 were 95.73% and 13.58%

respectively. C3 cell line could form colonies in soft agar

while C5 cell line failed to form colonies. The invasion and metastasis of C3 was stronger than that of C5 in vitro. The results showed that the tumorigenicity of C3 cell line was stronger than that of C5 cell line in vivo. Liver and kidney metastases from C3 were observed

while the C5 only spread to the kidneys. Conclusion: Aneuploidy may not be the only reason for the tumorigenicity of cancer cells. There is a correlation between aneuploidy and tumorigenicity of tumor cells. Aneuploidy contributes to malignant transformation and tumorigenesis of tumor cells.