HPD overexpression predicts poor prognosis in breast cancer

The enzyme, 4-hydroxyphenylpyruvate dioxygenase (HPD), is critical to tyrosine metabolism; its deficiency can cause tyrosinemia. However, its precise contribution to tumorigenesis is unclear. Here, we investigated the correlation between HPD expression and prognosis in patients with breast cancer.

145 breast cancer specimens were selected to analyze HPD protein expression by immunohistochemistry and evaluate its relationship to patients' clinicopathological features. HPD localization was confirmed in MCF-7 and MDA-MB-231 breast cancer cells, using immunofluorescence staining. The expression of HPD protein was detected in breast cancer and cancer-adjacent normal tissues using Western blot analysis. Survival rates were calculated by the Kaplan-Meier method.

We found that HPD protein was mainly located in the cytoplasm/nucleoli/perinucleus in breast cancer cells, as shown by immunofluorescence staining in MCF-7 and MDA-MB-231 cells, and immunohistochemistry in breast cancer and adjacent normal tissues (HPD protein expression-breast cancer: 46.9% [68/145], ductal carcinoma in situ [DCIS]: 22.6% [12/53], and normal tissues: only 4.8% [2/42]). Similarly, the Western blot results further confirmed the increased expression of HPD in breast cancer compared with cancer-adjacent normal tissues (P < 0.05). HPD expression level was positively correlated with histological grade and clinical stage, and inversely correlated with 10-year overall survival (OS) rates, in patients with breast cancer. Among patients with breast cancer, those with high HPD expression had worse OS rates than those with low HPD expression. Additionally, when patients were subgrouped by disease stage or grade, those with high HPD expression had worse OS rates than those with low HPD expression for each respective stage or grade.

Our findings indicate that HPD may be a useful prognostic predictor, and a potential therapeutic target for patients with breast cancer.