A protein best known as a water channel appears in more than a third of these breast cancer samples—and its presence is linked to poorer cancer-specific survival. The study asks whether AQP5 is simply a marker, or part of the biology behind aggressive disease.

Aquaporin water channels, or AQPs, have become an area of great interest in human carcinogenesis. This study examined AQP5 expression in breast cancer using 591 tissue samples with seven-year follow-ups. Immunochemistry analysis found AQP5 overexpression in thirty-six percent of cases, or two hundred twelve of five hundred ninety-one.

The analysis then focused on strong, three-plus expression in sixty cases. Strong AQP5 expression correlated positively with tumor grade and was more frequent in estrogen-receptor and progesterone-receptor-negative breast cancers.

Her2/neu-positive status also correlated positively with strong AQP5 expression. Patients with positive AQP expression had less favorable breast cancer-specific survival over seven years, and AQP5 expression was identified as an independent molecular marker associated with worse clinical outcomes.

Fluorescence in situ hybridization identified gene amplification in three of thirty readable breast cancers, suggesting that at least some AQP5 overexpression is associated with a genomic-level aberration. Aquaporins are a family of transmembrane water channel proteins widely distributed throughout the body.

They have been shown to play a key role in transcellular and transepithelial water movement. Two regions are critical for AQP function: the Asn-Pro-Ala, or NPA, regions and the aromatic-arginine region. The NPA regions connect to form an hourglass model.

Earlier studies found that AQP5 overexpression in NIH3T3 and BEAS-2 cells significantly activated Ras pathways, mediated by phosphorylation of the cAMP-protein kinase consensus site of AQP. Ectopic expression of human AQP5 in BEAS-2 cells induced phenotypic changes characteristic of transformation both in vitro and in vivo, apparently dependent on phosphorylation of a PKA consensus site in a cytoplasmic loop.

In lung cancer, more than four hundred resected non-small cell lung cancer samples showed varying AQP5 expression with significant prognostic implications. In breast cancer tissue samples, expressions of AQPs one, three, four, five, ten, eleven, and twelve were examined, with minimal expression in surrounding normal breast tissues.

AQP5 was expressed mainly in cell membranes in carcinoma tissues, while it was absent in normal breast tissues. A similar study found prominent AQP5 expression in breast cancer cells. The study examined AQP5 expression in a large cohort of five hundred ninety-one resected breast cancer samples.

It focused on the sixty cases with high-level AQP5 expression and their clinicopathological characteristics, including estrogen receptor, progesterone receptor, and HER2 status. Seven years of follow-up data were used to study the prognostic implications of overall AQP5 expression in two hundred twelve cases.

The study also examined AQP5 gene amplification as one possible cause of strong expression. Tissue microarrays were constructed from formalin-fixed, paraffin-embedded tissues from five hundred ninety-one breast cancer samples.

The samples came from the Department of Pathology at Asan Medical Center, with Internal Review Board approval. The breast samples were obtained between January nineteen ninety-three and December nineteen ninety-eight. Study pathologists reviewed the original hematoxylin and eosin-stained slides and arrayed representative tumor areas in triplicate.

The triplicated blocks were used to minimize tissue loss and overcome tumor heterogeneity. Some non-small cell lung cancer tissue-microarray samples served as a positive control for AQP5 expression. Two study pathologists, blinded to clinicopathologic variables, graded immunostaining semi-quantitatively using staining intensity and the percentage of positive tumor cells.

Staining intensity used four grades: zero for no staining, one for weak staining, two for moderate staining, and three for strong staining. The percentage of stained tumor cells used two grades: zero for less than ten percent and one for more than ten percent.

AQP5 expression was defined as positive when the product of intensity score and percentage score was one or more. Histological type and grade were confirmed on hematoxylin and eosin-stained tissue-microarray slides. The statistical analysis used the chi-square test with SPSS software, while mean patient age and tumor size were evaluated with a t-test.

Survival curves were produced using the Cox proportional hazards model to test the risk of cancer death. Prognostic factors were examined with both univariate and multivariate analyses. All p-values were two-sided, and differences at p less than zero point zero five were considered statistically significant.

Figure one shows AQP5 immunohistochemical staining across tissue samples, with brown staining indicating AQP5 expression. Panels a through c show non-small cell lung cancers with weak, moderate, and strong immunoreactivity, while panels d through f show the corresponding intensity categories in breast cancers.

This visual establishes how the authors classified AQP5 expression in the tissue microarray, supporting their larger clinical analysis of five hundred ninety-one breast cancers. Table one compares the sixty breast cancers with strong AQP5 expression among five hundred ninety-one patients, across demographics, tumor characteristics, and immunophenotypes.

Most clinicopathologic comparisons, including age, tumor size, T stage, N stage, and TNM stage, have p-values above zero point zero five, while grade shows p equals zero point zero zero six. The strongest statistical associations appear for ER status, with p equals zero point zero zero zero, PR status, with p equals zero point zero zero one, and HER2/neu status, with p equals zero point zero zero five, motivating the study’s later survival analysis.

Her2/neu-positive status was positively correlated with strong AQP5 expression, while the reported comparisons for estrogen-receptor and progesterone-receptor status showed higher strong-expression proportions in negative than positive groups. Among five hundred ninety-one patients, seven were male breast cancer patients.

Because this number was small, proper interpretation of clinicopathological characteristics based on gender difference was not feasible. The prognostic analysis included five hundred ninety-one patients, with overall survival followed for up to seven years after diagnosis.

Patients with positive AQP5 expression included two hundred twelve cases. The group with positive AQP5 expression had a less favorable breast cancer-specific survival rate, with a p-value of zero point zero zero eight.

After adjustment for histologic grade and tumor stage, AQP5 overexpression in two hundred twelve cases correlated with poorer disease-specific survival. The p-value was zero point zero three five, with a relative risk of one point five six seven and a ninety-five percent confidence interval from one point zero three two to two point three seven five.

AQP5 status was therefore identified as an independent molecular marker associated with worse clinical outcomes in breast cancer. This Kaplan–Meier plot compares breast cancer-specific survival over months for AQP5-positive and AQP5-negative groups. The curves separate over follow-up, with the figure reporting less favorable survival for the AQP5-positive group and a log-rank p-value of zero point zero zero eight.

Across 591 patients, the authors therefore identify AQP5-positive status as a marker associated with poorer clinical outcomes. To investigate mechanisms of AQP5 overexpression, fluorescence in situ hybridization identified evidence of gene amplification in three of thirty readable breast cancer cases.

The study therefore concluded that at least some AQP5 overexpression is associated with a genomic-level aberration. For the gene-amplification screen, breast cancer tissues with an AQP5 score of three and some with a score of two were reassembled into two tissue-microarray blocks, and fluorescence in situ hybridization was performed.

Figure three uses fluorescence in situ hybridization to look for AQP5 gene amplification in resected tumor tissue. The representative non-small-cell lung cancer image shows no amplification, consistent with the authors’ finding in all sixty tested cases, while breast-cancer examples include a negative case and positive cases with clustered red AQP5 signals alongside green control signals.

Amplification was detected in at least three of sixty breast cancers, suggesting that AQP5 overexpression can sometimes reflect a genomic alteration in breast cancer, but not in the tested lung cancers. Across 591 breast cancers, AQP5 positivity was associated with worse breast cancer-specific survival, while strong expression tracked with tumor grade and hormone-receptor status.

Gene amplification may explain at least some overexpression.