Mounting evidence indicates that signaling pathways implicated in development are altered in tumorigenesis as well [
1]. SLIT proteins bind ROBO proteins and are involved in axon guidance during development [
2]. In addition, SLIT/ROBO interactions play important roles in many processes, including apoptosis, motility, angiogenesis and invasion of cancer cells [
2]. For example, decrease of SLIT/ROBO interaction leads to loss of E-cadherin expression [
3,
4]. ROBO1-deficient mice suffer from cancer development [
5]. Axon guidance genes ROBO1 and ROBO2 are frequently lost in many cancers (head/neck, breast, lung, kidney and uterine cancers), and considered tumor suppressor genes (TSG) in them [
6‐
9]. In prostate cancers (PCA), mRNA expression of axon guidance genes were frequently altered [
10]. ROBO1 mRNA expression was down-regulated compared with normal prostate tissues, while ROBO2 mRNA expression was not altered [
10]. However, it remains unclear whether ROBO1 and ROBO2 expression is altered in PCA at protein level. In this study, we analyzed expression of ROBO1 and ROBO2 proteins in PCA tissues.