Introduction. The biological role of amyloid precursor protein (APP) is not well understood, especially in testicular germ cell tumors (TGCTs). Therefore, we aimed to investigate the immunoreactivity (IR) and expression of APP in TGCTs and evaluated its clinical relevance. Materials and Methods. We performed an analysis of immunohistochemistry and mRNA expression of APP in 64 testicular specimens and 21 snap-frozen samples obtained from 1985 to 2004. We then evaluated the association between APP expression and clinicopathological status in TGCTs. Results. Positive APP IR was observed in 9.8% (4/41) of seminomatous germ cell tumors (SGCTs) and 39.1% (9/23) of nonseminomatous germ cell tumors (NGCTs). NGCTs showed significantly more cases of positive IR and a higher mRNA expression level compared with those of SGCTs . Positive APP IR was also significantly associated with α-fetoprotein (αFP) elevation and venous invasion . Conclusion. We observed an elevated APP expression in TGCTs, especially in NGCTs. APP may be associated with a more aggressive cancer in TGCTs. 1. Introduction Testicular cancer is a relatively rare cancer that accounts for approximately 1–1.5% of male cancers, and 90–95% of these cancers are testicular germ cell tumors (TGCTs) [1]. TGCTs can be classified into two major histological categories, namely, seminomatous germ cell tumor (SGCT) and nonseminomatous germ cell tumor (NGCT). NGCTs, which include yolk sac tumors, embryonal cell carcinomas, teratomas, and choriocarcinomas, are different from SGCTs with regard to clinical characteristics and therapy required. Amyloid precursor protein (APP) is a type 1 transmembrane protein that is considered to play a key role in Alzheimer’s disease. It has multiple isoforms attributable to alternative splicing and is expressed in various types of human cells. APP695 predominantly exists in the neurons whereas other isoforms such as the APP751 and APP770 are expressed in nonneuronal cells [2]. The biological role of APP is not well understood. APP and its cleaved forms have been suggested to mediate various functions, including cell adhesion [3], cell signaling [4], and cell growth [5–7]. These functions are important in carcinogenesis, and APP expression may be involved in the development of various cancers [8–13]. We have previously shown that APP is a primary androgen-responsive gene that promotes the growth of prostate cancer cells [14]. In the present study, we investigated APP immunoreactivity (IR) and APP mRNA expression in TGCTs and evaluated its clinical significance. 2. Materials and
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