OBJECTIVETo detect the expression of aquaporin 1 (AQP1) in breast cancer tissues, and to analyze its relationship with clinicopathological characteristics and prognosis of breast cancer patients.

METHODSHistochemical SP staining was used to assess the AQP1 expression in 30 cases of lobular hyperplasia of mammary gland, 16 cases of ductal carcinoma in situ (DCIS), and 78 cases of invasive ductal carcinoma-not otherwise specified (IDC-NOS), and to analyze the relationship between cytoplasmic expression of AQP1 in IDC-NOS and clinical pathological characteristics and prognosis of the patients.

RESULTSPositive AQP1 immunolabelling appeared as brown deposit over the membrane of myoepithelial cells in all cases of lobular hyperplasia of mammary gland, but only 10.0% of cases showed cytoplasmic staining in glandular epithelial cells. In the ductal carcinoma in situ, brown deposit of AQP1 immunolabelling appeared over the myoepithelial cell membrane in all cases, but only 12.5% of cases were accompanied with cytoplasmic staining in glandular epithelial cells. In the invasive ductal carcinoma not otherwise specified, 35.9% of the cases showed cytoplasmic AQP1 immunoreactivity, but only 3.8% of cases showed positive membrane staining of the tumor cells. There were highly positive AQP1 expression in 14 cases, weakly positive in 14 cases, and negative in 50 cases. Cytoplasmic AQP1 expression in the IDC-NOS cases was significantly correlated with pathologic stage, PR, HER-2, lymph node status, Nottingham prognostic index (NPI) and metastasis or recurrence (all P < 0.05). The 5-year progression-free survival (PFS) rates were 16.8% in the patients with strong positive AQP1 expression, 90.9% in the cases with weakly positive AQP1 expression and 94.9% in the AQP1-negative cases, showing a significant difference (P < 0.05). Multivariate analysis indicated that the lymph node status and cytoplasmic expression of AQP1 were independent factors for PFS (both P < 0.05). The 5-year overall survival (OS) rates were 45.6% in the AQP1- strong positive cases, 90.0% in the AQP1-weakly positive cases and 97.7% in the AQP1-negative cases, showing a significant difference (P < 0.05). Multivariate analysis indicated that the lymph node status and cytoplasmic expression of AQP1 were independent factors affecting the overall survival and progression-free survival (both P < 0.05).

CONCLUSIONAQP1 is mainly expressed on the membrane of myoepithelial cells in the benign breast lesions, but in the cytoplasm of breast cancer cells, and its expression is an independent factor affecting prognosis of breast cancer patients.