**7. AQPs: cancer diagnostic markers in breast cancer**

There is no clinical data so far which confirms the use of AQPs as diagnostic markers for breast cancer. However, many reports suggest a strong correlation between the expression profile of certain types of AQPs and breast cancer pathogenesis and prognosis. For example, AQP 1 expression was associated with poor clinical prognosis in ductal type, ER −ve and HER2/neu −ve breast cancer patients [132]. The cytoplasmic expression of AQP 1 was also correlated with advanced pathological features of invasive ductal carcinoma, lymph node metastasis and shorter survival [134]. Overexpression of AQP 3 in HER2-overexpressing patients [137] as well as in premenopausal ER+ve breast cancer patients [138] was associated with advanced stage. AQP 5 expression was also shown to be associated with poor clinical prognosis [133], partic‐ ularly in patients with ER/PR+ve tumors [142], and in the ductal epithelial cells of human breast tissues [143].

Detection of serum AQP 4 auto-antibodies has shown promising indication as a diagnostic tool in neuromyelitis optica (NMO), an inflammatory demyelinating disease that selectively affects optic nerves and spinal cord. It is claimed to be significantly associated with a higher number of relapses and longer disease duration [146, 147]. There are also reports suggesting a role for other AQPs: AQP 2 in determining the etiology of metabolic disorders dependent on the arginine vasopressin [148], AQP 3 in eczema [149] and AQP 4 in epilepsy [150].
