Moreover, we speculate that SCF may induce c-Kit expression through a positive-feedback loop, a possibility supported by our observation that expression levels of SCF and c-Kit were highly correlated in the cases with perineural invasion. This finding is in agreement with a recent report: c-Kit-negative PC3 prostate cancer cells gained c-Kit expression when the cells developed metastasized bone tumors in xenograft mice, where the bone marrow stromal cells expressed SCF [21]. The study may offer a valuable clue about why slow-growing ACCs become aggressive

when the tumors invade the neural space or metastasize to bone. In this work, we performed phospho-ERK1/2 IHC simply as a way to facilitate analysis. Our choice of this approach Proteasome inhibitor was not intended to imply that ERK1/2 is phosphorylated only by SCF-mediated c-Kit activation. Moreover, the results were variable between cases likely owing to the nature of antigenicity of phosphorylated protein. A recent study showed that phosphorylated-ERK1/2

in primary tumors was largely degraded in the process of formalin-fixation [22]. The extreme rarity of ACC limits the fresh tissue donor pool. In addition, phospho-c-Kit IHC with FFPE samples is not yet established. Thus, in light of these limitations, we believe that using phospho-ERK1/2 IHC with FFPE samples is the most practical approach for accomplishing our purpose. There was a substantial increase Selleckchem Thiazovivin of active ERK1/2 protein in more than 20% of ACC tumor cells. We found that immunoreactivity was greater in the outer myoepithelial cells than in the inner duct-type epithelial cells. The difference

could be attributed Farnesyltransferase to the characteristic difference between two cell types in ACC. c-Kit protein is specifically elevated in duct-type epithelial cells, whereas EGFR expression is limited to the myoepithelial cells [12]. Moreover, a differentiation marker p63 is predominantly found in the myoepithelial but not duct-type epithelial component [23]. Thus, ERK1/2 activation appeared to be accelerated in differentiated cells in ACC. In this paper, we found that the highest quartile of c-Kit mRNA expression was cross-correlated with short-term poor prognosis. Because quantitative PCR is sensitive, reproducible and reliable for determining the level of c-Kit mRNA, this gene expression analysis may have a larger potential to identify the patients more likely to benefit from c-Kit-targeted therapies in ACC [24] and [25]. These therapies may include targeting c-Kit protein or upstream molecules that regulate it. It has been suggested that c-Kit is a downstream transcriptional target of MYB, which is activated by gene fusion with nuclear factor nuclear factor I/B (NFIB) in roughly half of ACC tumors [26] and [27].