ALDH1-positive intratumoral stromal cells indicate epithelial differentiation and good prognosis in prostate cancer
Aldehyde dehydrogenase 1 (ALDH1) characterizes tumor-initiating cells in solid tumors, however little is known about its expression in intratumoral stromal cells. Herein, we aimed to dissect its potential dual relevance in prostate cancer (PCa). ALDH1 expression was evaluated immunohistochemically in tumor and stromal cells in primary PCa and metastasis. It was correlated with clinico-pathological parameters, outcome of patients, and selected protein expression (CK5/6, CK14, CK8/18, CK19,
... CK8/18, CK19, EpCAM, Ki-67, E-cadherin, N-cadherin, and vimentin). ALDH1 protein was detected in tumor and stromal cells in 16% and 67% of 348 primary PCa, respectively. Tumor cell ALDH1 expression was associated with advanced tumor (T) status (p=0.009), higher Gleason score (p=0.016), shorter time to biochemical recurrence (BR) (p=0.010) and CK14 expression (p=0.023). Stromal cell ALDH1 expression correlated with lower T status (p=0.008), N0 status (p=0.017), lower Gleason score (p=0.016) and longer time to BR (p=0.017). In the subgroup of dAmico high-risk patients it occurred even to be an independent predictor of good prognosis (multivariate analysis, p=0.050). ALDH1 was found in stroma of tumors characterized by CK8/18 (p=0.033) or EpCAM expression (p<0.001) and rarely by epithelial-mesenchymal transition defined as CK8/18(-)vimentin(+) phenotype (p=0.003). ALDH1 was detected in tumor cells and stroma of 33% and 41% of hormone naive lymph node metastases (n=63), 52% and 24% of castration resistant bone metastases, as well as 89% and 28% of castration resistant visceral metastases (n=21), respectively. We have determined that contrary to tumor cell ALDH1, the presence of stromal ALDH1 is associated with a more differentiated tumor epithelial phenotype in primary PCa, improved clinical outcome, and is less frequent in PCa metastases.