HOX genes are vital for all aspects of mammalian growth and differentiation, and their dysregulated expression is related to ovarian carcinogenesis. The aim of the current study was to establish the prognostic value of HOX dysregulation as well as its role in platinum resistance. The potential to target HOX proteins through the HOX/PBX interaction was also explored in the context of platinum resistance. HOX gene expression was determined in ovarian cancer cell lines and primary EOCs by QPCR, and compared to expression in normal ovarian epithelium and fallopian tube tissue samples. Statistical analysis included one-way ANOVA and t-tests, using statistical software R and GraphPad. The analysis identified 36 of the 39 HOX genes as being overexpressed in high grade serous EOC compared to normal tissue. We detected a molecular HOX gene-signature that predicted poor outcome. Overexpression of HOXB4 and HOXB9 was identified in high grade serous cell lines after platinum resistance developed. Targeting the HOX/PBX dimer with the HXR9 peptide enhanced the cytotoxicity of cisplatin in platinum-resistant ovarian cancer. In conclusion, this study has shown the HOX genes are highly dysregulated in ovarian cancer with high expression of HOXA13, B6, C13, D1 and D13 being predictive of poor clinical outcome. Targeting the HOX/PBX dimer in platinum-resistant cancer represents a potentially new therapeutic option that should be further developed and tested in clinical trials.Ovarian cancer is the 5th leading cause of cancer death in women in the western world and it is estimated there were 22,280 new cases and 15,500 deaths due to the disease in the US in 2012. 1 It is the most lethal of the gynaecological malignancies largely due to late diagnosis. Standard treatment involves debulking surgery followed by a combination of taxane and platinum-based therapy. Initially most women respond to platinum-based therapy, but the majority suffer disease recurrence due to drug resistance. It is therefore essential to introduce new therapeutic approaches to improve treatment at diagnosis and/or provide an effective second line treatment.There are different types of ovarian cancer classified by the cell type they originate from. The most common form, accounting for >90% of ovarian cancers, is epithelial ovarian cancer (EOC), and the high grade serous (HGS) subtype accounts for 80% of EOC cases.The epithelial ovarian tumours undergo M€ ullerian differentiation, which suggests that differentiation-regulatory factors may contribute to their progression. This mechanism has been shown to involve homeobox (HOX) genes 2,3 which play important roles in tissue differentiation during embryonic development. The HOX genes constitute a family of transcription factors, and in mammals 39 HOX genes have been identified. They are organised into 4 paralogous clusters (A, B, C and D) located on 4 different chromosomes. During development of the female reproductive system four HOX genes, HOXA9, HOXA10, HOXA11 and HOXA13 are expressed uniformly along the M€ uller...