Abstract. HOX genes are known not only as master genes that control the morphogenesis, but also as regulator genes that maintain tissue or organ specificity in the adult body. We hypothesized that dysregulated expression of HOX genes was associated with tumor development and malignant progression such as invasion and metastasis. In this study, we analyzed the expression patterns of 39 HOX genes in human invasive ductal breast cancer tissues and normal tissues by the real-time RT-PCR method. We found 11 HOX genes (HOXA1, A2, A3, A5, A9, C11, D3, D4, D8, D9 and D10) expression levels of which were significantly different between cancerous and normal tissues. All 10 genes except HOXC11 were expressed at lower levels in cancerous tissues than normal tissues. Comparing expression levels of each HOX gene among the different types of cancer tissues, the expression level of HOXB7 was lower in lymph node metastasis-positive cancer tissues than negative cancer tissues; those of HOXD12 and D13 were higher in progesterone receptor-positive cancer tissues than negative cancer tissues; and the expression level of HOXC5 was lower in cancerous tissues with mutated-type p53 than in normal and cancerous tissues with wild-type p53. These results suggest that the aberrant expression of HOX genes is related to the development of breast cancer and malignant behavior of cancer cells.

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