Expression of KAI1/CD82 in distant metastases from estrogen receptor-negative breast cancer

The tetraspanin protein superfamily member KAI1 suppresses tumor growth and metastasis in animal models and is downregulated in various human malignancies. In breast cancer, KAI1 is preferentially lost in estrogen receptor (ER)-positive tumors. Interestingly, most ER-negative primary breast cancers retain KAI1 expression. This study aimed to evaluate whether or not KAI1 is downregulated during progression to metastasis of these carcinomas. Expression of KAI1, ER, progesterone receptor, c-ErbB2, and Ki67 was analyzed in tissue microarrays comprising a large collection of distant organ metastases from human breast cancers ( n  = 92) by immunohistochemistry. Results were compared with a previously characterized set of primary breast tumors ( n  = 209). Immunoreactivity for KAI1 was observed in one-third of the metastases and was associated with lack of ER expression ( P  = 0.005). The high frequency of KAI1-positive cases in ER-negative primary tumors was maintained in ER-negative metastases. Expression of KAI1 was also observed in MDA-MB-468 and SK-BR-3, two ER-negative breast cancer cell lines of metastatic origin. Moreover, a reanalysis of independent microarray gene expression data indicated maintenance of KAI1 mRNA expression in metastases from ER-negative breast cancers. Furthermore, in a series of matched pairs of mammary carcinomas and metachronous distant metastases, all metastases from KAI1-positive/ER-negative primary tumors were KAI1-positive as well. Collectively, these findings demonstrate that the expression of KAI1 is maintained during progression to metastasis in a large proportion of ER-negative mammary carcinomas. This has significant implications for the use of KAI1 as a clinical marker and the understanding of the metastatic process in human breast cancer. ( Cancer Sci 2009; 100: 1767–1771)     

Transduction of KAI1/CD82 cDNA promotes hematogenous spread of human lung-cancer cells in natural killer cell-depleted SCID mice.

KAI1, which is identical to CD82, was initially identified as a metastasis-suppressor gene for human prostate cancer, and its expression is reported to be a favorable prognostic factor for operable human lung cancer. In this study, we examined the functional role of KAI1/CD82 in the late phase of metastatic spread of human lung-cancer cells. For this, KAI1/CD82 cDNA was introduced into KAI1/CD82 low-expressing human lung-cancer cell lines, SBC-3 and PC-14, and then the metastatic potential of the transformants was analyzed by i.v. inoculation of KAI1/CD82-transduced cells, SBC-3/KAI1 and PC-14/KAI1, into NK cell-depleted SCID mice. Contrary to our expectations, KAI1/CD82 gene transfer promoted multiorgan metastasis of i.v.-inoculated human lung-cancer cells, while s.c. tumor growth was unaffected. Cancer cells from metastatic tumors of NK cell-depleted SCID mice injected i.v. with SBC-3/KAI1 expressed appreciable cell-surface KAI1/CD82, and cells not expressing KAI1/CD82 (revertants) were not detected in the tumors. Our findings indicate that under conditions where the host's natural cytotoxicity is suppressed, KAI1/CD82 may enhance the formation of tumors by circulating lung-cancer cells at metastatic sites.     

Expression Levels of Tetraspanin KAI1/CD82 in Breast Cancers in North Indian Females

Background: Carcinogenesis is a multifaceted intricate cellular mechanism of transformation of the normal functions of a cell into neoplastic alterations. Metastasis may result in failure of conventional treatment and death Hence, research on metastatic suppressors in cancer is a high priority. The metastatic suppressor gene CD82, also known as KAI1, is a member of the transmembrane 4 superfamily which was first identified in carcinoma of prostate. Little work has been done on this gene in breast cancer. Herein, we aimed to determine the gene and protein level expression of CD82/KAI1 in breast cancer and its role as a prognosticator. Materials and Methods: In this study, 83 histologically proven cases of breast cancer and a similar number of controls were included. Patient age ranged from 1870 years. Quantitative Real Time Polymerase Chain Reaction (qRT PCR) and immunohistochemistry (IHC) were used to investigate KAI1 expression at gene and protein levels, respectively. Statistical analysis was done to correlate expression of KAI1 and clinicopathological parameters. Results: It was revealed that: (i) KAI1 was remarkably diminished in metastatic vs non metastatic breast cancer both at the gene and the protein levels (P<.05); (ii) KAI1 expression levels were strongly correlated with TNM staging, histological grade and advanced stage (p<0.001) and no association was found with any other studied parameter; (iii) Lastly, a significant correlation was observed between expression of KAI1 and overall median survival of BC patients (P 0.04). Conclusions: Our results suggest that lack of expression of the KAI1 might indicate a more aggressive form of breast cancer. Loss of KAI1 may be considered a significant prognostic marker in predicting metastatic manifestation. When evaluated along with the clinical and pathological factors, KAI1 expression may be beneficial to tailor aggressive therapeutic strategies for such patients.     

Loss of KAI1 expression in the progression of colorectal cancer

The transmembrane 4 superfamily member KAI1 (CD82) has been shown to inhibit pulmonary metastases in experimental metastasis models of prostate cancer and melanoma. KAI1 expression is decreased in the progression of common solid epithelial tumors of adulthood, including lung, prostate, breast, esophageal, gastric, pancreatic, and bladder cancers. The purpose of our study was to investigate KAI1 expression in the progression of human colorectal cancer. We first analyzed 20 colorectal cancer cell lines by immunoblot techniques. KAI1 was expressed heterogeneously, with the tumor cell lines having a more complex degree of glycosylation compared with that of the normal colonic tissue. KAI1 was highly expressed in the primary SW480 colon cancer cell line but was down-regulated 15-fold in the matched metastatic SW620 cell line. We also investigated KAI1 protein expression by immunohistochemistry in tissues from 84 patients with colorectal cancer. Each tissue section was assigned a KAI1 mean score (KMS) from 0 to 300 based on the product of the percentage of cells that stained for KAI1 and the intensity of the stain (1, 2, or 3). In 84 patients with colorectal cancer, KAI1 was expressed at high levels in normal colonic mucosa (KMS 226) but was expressed at lower levels in the primary tumors (KMS 65; P < 0.0001). In a subset of 12 patients with stage IV metastatic disease, we observed a progressive down-regulation of KAI1, from the normal adjacent colonic mucosa (KMS 193) to the primary tumor (KMS 72; P = 0.0001) to the liver metastasis (KMS 25; tumor compared with metastasis, P = 0.0135). We found no correlation between loss of KAI1 expression and stage of disease. In 10 patients, we also noted loss of KAI1 expression in the transition from normal colonic mucosa (KMS 237) to adenoma (KMS 174) to carcinoma (KMS 62; P < 0.0167 for all three comparisons). We conclude that the down-regulation of KAI1 occurs early in the progression of colorectal cancer.     

肾癌KAI—1基因表达与浸润转移的关系

目的　研究ＫＡＩ１ 基因在肾细胞癌的表达状况。　方法　采用逆转录多聚酶链反应（ＲＴＰＣＲ） 技术检测２２ 例肾癌及２２ 例非癌肾组织ＫＡＩ１ ｍ ＲＮＡ 的表达。　结果　１６ 例肾癌及２２ 例非癌肾组织表达ＫＡＩ１ ｍＲＮＡ，癌组织的表达阳性率显著低于非癌组织（ Ｐ＜ ００５） ；有肾外浸润或淋巴结转移移的肾癌组织阳性率显著低于无浸润转移者（ Ｐ＜ ００１）。　结论　ＫＡＩ１ 基因的低表达可促进肾癌细胞转移。     

KAI1 protein is down-regulated during the progression of human breast cancer.

The KAI1 gene was identified as a metastasis suppressor gene for human prostate cancer. Recently, we showed that KAI1 mRNA levels were higher in an immortal, normal-like breast epithelial cell line and nonmetastatic breast cancer cell lines but lower substantially in highly metastatic breast cancer cell lines. In this study, we examined KAI1 protein expression in breast cancer cell lines by Western blot and immunohistochemical study. KAI1 protein levels paralleled KAI1 mRNA levels and were inversely correlated with the metastatic potential of breast cancer cells. Furthermore, we examined KAI1 protein expression immunohistochemically in specimens from 81 patients with breast cancer and then correlated the findings with the clinical and histopathological parameters of the patients. High levels of KAI1 protein expression were found in normal breast tissues and noninvasive breast cancer (ductal carcinoma in situ). In contrast, KAI1 expression was reduced in most of the infiltrating breast tumors. We found that, in general, more malignant tumors demonstrated significantly lower KAI1 expression (P = 0.004). Additionally, among 29 specimens demonstrating multiple stages of malignancy within a single specimen, 23 demonstrated significant differences in KAI1 expression between benign breast tissue, ductal carcinoma in situ, and invasive carcinoma. The higher the incidence for malignancy within a given specimen, the lower the KAI1 expression (P < 0.001). These data suggest that in advanced breast cancer, KAI1 expression is down-regulated. Therefore, KAI1 may be a potentially useful indicator of human breast cancer progression.     

Frequent loss of expression of the cyclin-dependent kinase inhibitor p27(Kip1) in estrogen-related Endometrial adenocarcinomas.

PURPOSE: p27(Kip1) is a member of the Cip1/Kip1 family of cyclin-dependent kinase inhibitors and is a potential tumor suppressor gene. Low levels of p27 are associated with poor prognosis in a variety of gynecological tumors, including breast, ovarian, and cervical carcinomas. The role of p27 in endometrial cancer remains controversial. EXPERIMENTAL DESIGN: In the present study, p27 protein expression was investigated by immunohistochemistry in a series of 217 endometrial adenocarcinomas and, where present, in synchronous normal endometrium, simple and complex hyperplasia (with or without atypia), and cystic atrophy. The relationship between p27 expression and clinical outcome was also evaluated. RESULTS: Immunohistochemical analysis revealed a significant loss of p27 expression from normal (33%) through hyperplastic endometrium (50%) to endometrial adenocarcinomas (71%; P 相似文献   

Clinical implications of mRNA expression of KAI1 in ovarian cancer with or without metastasis

Background. KAI1 is a potential metastasis suppressor gene for prostate cancer. Decreased expression of KAI1 mRNA has been shown to be associated with the formation of metastasis and the progression of prostate, lung, breast, pancreatic, and bladder cancer. It has also been reported, however, that KAI1 expression is unchanged in metastatic and nonmetastatic esophageal and gastric cancer. We performed the present study to investigate the function of KAI1 in the progression and/or metastasis of ovarian cancer. Methods. We investigated the mRNA expression levels of the KAI1 gene, using quantitative polymerase chain reaction (PCR), in 29 ovarian tumors (1 adenoma, 2 low- malignant potential tumors, 9 adenocarcinomas without metastasis, and 17 adenocarcinomas with metastasis), seven ovarian cancer cell lines, and two normal ovaries. Using a thermal cycler, we found that the KAI1 gene was amplified in parallel with an internal control gene, β-Actin. The relative expression ratio (KAI1/β-Actin) as measured by densitometry was used to evaluate gene expression. Immunohistochemical localization of the KAI1 protein in ovarian cancer tissues was confirmed by the avidin-biotin peroxidase complex (ABC) method. Results. The mRNA expression levels of KAI1 were consistent in normal ovary, ovarian tumor samples, and ovarian cancer cell lines. No statistically significant difference in the KAI1 mRNA expression level was found in ovarian cancer samples with or without metastasis. Immunohistochemistry revealed that the KAI1 protein was expressed in the cell membranes of ovarian cancer cells. Conclusions. Our results suggest that reductions in KAI1 mRNA expression are not involved in either the progression or metastasis of ovarian carcinomas. Received: April 22, 1999 / Accepted: July 26, 1999     

Maspin和Ki67在子宫内膜癌中的表达及其相关性分析

目的:探讨在正常子宫内膜、子宫内膜增殖症(非典型)和子宫内膜癌中Maspin和Ki67的表达、相关性及与临床病理特征的关系.方法:采用免疫组织化学方法检测Maspin和Ki67在30例正常增生期子宫内膜、40例子宫内膜增殖症(非典型)和72例子宫内膜癌中的表达.结果:在子宫内膜癌中,Ki67表达分别显著高于正常子宫内膜和子宫内膜增殖症(P =0.043;P =0.020),Maspin表达分别显著高于正常子宫内膜和子宫内膜增殖症(P ＜0.05);Ki67与子宫内膜癌的组织学分级和分期有统计学差异(P＜0.05),Maspin与子宫内膜癌的组织学分级、分期和淋巴结转移有统计学差异(P＜0.05),Maspin和Ki67表达呈正相关(r=0.231,P =0.005).结论:在子宫内膜癌中,Maspin和Ki67的表达提示两者可能成为子宫内膜癌的预后因子.     

Mutation and expression of the metastasis suppressor gene KAI1 in esophageal squamous cell carcinoma

BACKGROUND: KAI1/CD82, a tumor metastasis suppressor gene, is correlated inversely with the progression and invasion of several tumors. It also has been reported that the KAI1 gene is related to the tumor suppressor gene p53. This study was performed to clarify the correlation between KAI1/CD82 expression and clinicopathologic characteristics and p53 expression in patients with esophageal squamous cell carcinoma (ESCC). The authors also investigated mutation of the KAI1 gene coding region to determine whether this may reduce KAI1 expression in ESCC. METHODS: Using immunohistochemistry with anti-KAI1 polyclonal antibody and monoclonal antibody against p53, KAI1/CD82 and p53 expression were detected in 55 patients with ESCC who had undergone surgery. The authors examined the KAI1 gene mutation in 22 patients with ESCC by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and DNA sequencing. RESULTS: KAI1/CD82 expression was positive in 36 of 55 patients (65.5%). There was a significant inverse correlation between KAI1/CD82 expression and regional lymph node metastasis (P = 0.0045), distant metastasis (P = 0.0092), the number of lymph node metastases (P = 0.0019), and pathologic stage (P = 0.0046). The survival rates of KAI1/CD82 negative patients were poorer than those of positive patients (P = 0. 024). The correlation between KAI1 positive and p53 positive tumors was not statistically significant. None of the 22 patients with ESCC showed mutation of the KAI1 gene by PCR-SSCP. In one patient, there was polymorphism in the SSCP assay and DNA sequencing. CONCLUSIONS: The authors demonstrated immunohistochemically that the expression of KAI1 protein appeared to be correlated with lymph node metastasis. Mutation does not seem to be a mechanism for dysregulation of the KAI1 protein in ESCC.     

Expression and prognostic significance of urokinase and plasminogen activator inhibitor type-1 in endometrial hyperplasia and cancer

Proteolytic enzymes, like urokinase (uPA) and plasminogen activator inhibitor type-1 (PAI-1), are involved in remodelling tissues during invasion and metastasis of tumor cells. The purpose of the study is to evaluate the expression and the prognostic significance of these enzymes in endometrial hyperplasia and cancer. We used immunohistochemical staining to localize uPA and PAI-1 antigens and evaluate their expression, and the enzyme-linked immunosorbent assay (ELISA) to measure their levels during the progression of endometrial carcinoma. The results show that the levels of uPA and PAI-1 detection are systematically weak in simplex hyperplasia and are moderate in complex hyperplasia. In the endometrial carcinoma a very strong reaction was observed in the most aggressive variant of epithelial tumors. A positive signal for uPA was found only in the cytoplasm of normal and hyperplastic cells while, in tumors, uPA was present also in the cellular areas surrounding the neoplastic glands and at the apex of the malignant cells. The PAI-1 immunoreactivity was weak to moderate in 95.4% of carcinomas, with a diffuse signal mostly distributed in the cytoplasm of neoplastic cells and tumor stroma. UPA antigen concentrations were significantly higher in endometrial carcinoma than in endometrial hyperplasia (p<0.05) and in normal endometrium (p<0.001). PAI-1 antigen concentrations in carcinoma samples were significantly higher than in normal endometrium (p=0.002), but the difference was not statistically significant with respect to that in endometrial hyperplasia. We did not find any correlation between uPA and PAI-1 concentrations and the standard prognostic parameters for evaluating endometrial carcinoma. In conclusion, this study demonstrates that in hyperplastic endometria and in endometrial carcinoma there is a progressive increase in expression of uPA and PAI-1 than in normal endometrial tissue. In carcinoma tissues, the high expression of uPA is unregulated in the surrounding stroma tissue, particularly in the most aggressive histopathologic variants. UPA and PAI-1 may be factors associated with invasive behavior in endometrial carcinoma independent of other clinicopathological parameters.     

Loss of PTEN expression is associated with metastatic disease in patients with endometrial carcinoma

BACKGROUND: The PTEN tumor suppressor gene frequently is involved in endometrial carcinoma. Loss of heterozygosity and mutations reportedly are common, although the biologic importance of these changes remain largely unknown. The objective of this study was to assess the pattern of PTEN expression by immunohistochemistry in a large series of patients with endometrial carcinoma. METHODS: A population-based series of 316 patients with endometrial carcinoma who had long and complete follow-up was investigated for PTEN expression and its correlation with clinicopathologic variables, tumor markers, and survival. RESULTS: PTEN protein expression was mainly cytoplasmic in tumor cells, with no expression seen in 56 of 279 patients (20%) who had evaluable results. A heterogeneous staining pattern was found in 70 tumors (25%). A significant association between the loss of PTEN expression and metastatic disease was identified (P = 0.05). However, PTEN staining did not influence survival significantly. CONCLUSIONS: The loss of PTEN expression is relatively frequent in endometrial carcinoma and is associated significantly with metastatic disease. This indicates that the PTEN system plays an important role in some endometrial carcinomas, but further studies of PTEN protein expression related to various genetic alterations are necessary.     

Reduced Invasive and Metastatic Potentials of KAI1-transfected Melanoma Cells

KAI1 is a metastasis suppressor gene for human prostate cancer. To reveal the effect of KAI1 on the in vivo metastasis of tumors other than prostatic cancer, we transfected a human KAI1 cDNA into highly metastatic B16-BL6 murine melanoma cells and established stable transfectant clones with different expression levels of KAI1 message. The following results were obtained with the use of those transfectants. (1) Cell aggregation assay revealed a significantly enhanced Ca²⁺-independent aggregation of B16-BL6 cells by KAI1 cDNA transfection compared with mock transfectants ( P <0.01). (2) The in vivo phagokinetic activity and invasive ability of KAI1 transfectants were clearly decreased as compared with those of mock transfectants ( P <0.01). There was no significant effect of KAI1 expression on the in vitro or in vivo proliferation of B16-BL6 cells. (3) Lung colony formation of intravenously injected KAI1 transfectants in nude mice was significantly reduced as compared with mock transfectants or parental B16-BL6 cells ( P <0.01). These data suggest that KAI1 expression gives rise to the suppression of invasive and metastatic potentials of B16-BL6 cells.     

KAI1/CD82 expression as a prognosic factor in sporadic colorectal cancer

BACKGROUND: Since its identification as a suppressor gene for prostate cancer metastasis, down-regulation of KAI1/CD82 in a variety of malignancies has been reported. MATERIALS AND METHODS: Using immunohistochemistry, we examined KAI1/CD82 expression in surgical specimens obtained from 70 patients with advanced colorectal cancer and its correlation with clinicopathological factors, to clarify their prognostic significance. RESULTS: KAI1/CD82 expression was positive in 55% of the 70 colorectal cancers. There were statistically significant correlations between KAI1/CD82 expression and Dukes' stage, venous invasion, lymph node metastasis, tumor differentiation and liver metastasis. The significant correlation between KAI1/CD82 expression and outcome among patients with Dukes' C cancer (p=0.024) is particularly noteworthy. On multivariate analysis, KAI1/CD82 expression and Dukes' stage were identified as significant and independent prognostic factors (p=0.006 and 0.045, respectively). CONCLUSION: KAI1/CD82 expression closely correlates with clinicopathological factors for colorectal cancers. KAI1/CD82 expression appears to be a useful prognostic marker.     

Microarray analysis of endometrial carcinomas and mixed mullerian tumors reveals distinct gene expression profiles associated with different histologic types of uterine cancer.

Previous studies using cDNA microarray have indicated that distinct gene expression profiles characterize endometrioid and papillary serous carcinomas of the endometrium. Molecular studies have observed that mixed mullerian tumors, characterized by both carcinomatous and sarcomatous components, share features that are characteristic of endometrial carcinomas. The objective of this analysis was to more precisely define gene expression patterns that distinguish endometrioid and papillary serous histologies of endometrial carcinoma and mixed mullerian tumors of the uterus. One hundred nineteen pathologically confirmed uterine cancer samples were studied (66 endometrioid, 24 papillary serous, and 29 mixed mullerian tumors). Gene expressions were analyzed using the Affymetrix Human Genome Arrays U133A and U133B Genechip set. Unsupervised analysis revealed distinct global gene expression patterns of endometrioid, papillary serous, mixed mullerian tumors, and normal tissues as grossly separated clusters. Two-sample t tests comparing endometrioid and papillary serous, endometrioid and mixed mullerian tumor, and papillary serous and mixed mullerian tumor pairs identified 1,055, 5,212, and 1,208 differentially expressed genes at P < 0.001, respectively. These data revealed that distinct patterns of gene expression characterize various histologic types of uterine cancer. Gene expression profiles for select genes were confirmed using quantitative PCR. An understanding of the molecular heterogeneity of various histologic types of endometrial cancer has the potential to lead to better individualization of treatment in the future.     

KAI1/CD82 is a novel target of estrogen receptor-mediated gene repression and downregulated in primary human breast cancer

The cell-surface glycoprotein KAI1 suppresses tumor growth and metastasis in various animal models. Downregulation of KAI1 has been implicated in the progression of cancer. However, the mechanisms of KAI1 inactivation are poorly understood. This is the first study that investigates expression and regulation of KAI1 in human breast cancer. KAI1 expression was analyzed on custom-made tissue microarrays comprising 209 well-characterized breast cancers and normal mammary gland tissue. Strong KAI1 immunoreactivity was observed throughout the normal mammary gland epithelium. In breast cancer tissue, KAI1 immunoreactivity was lost in 161/209 (77%) cases. Strikingly, KAI1 was preferentially lost in estrogen receptor (ER)-positive breast cancers (p < 0.001). This was validated by real-time RT-PCR analyses showing a 7.5-fold downregulation of KAI1 mRNA in ER-positive relative to ER-negative tumors (p = 0.028). Notably, this was also corroborated by Affymetrix microarray expression data of an independent cohort of 49 breast cancers. Class comparison analysis identified KAI1 as downregulated in ER-positive tumors. Subsequently, human breast cancer cell lines were employed to test a potential role of ER-activity in the downregulation of KAI1, as suggested by our expression analyses. Exposure of ER-positive breast cancer cells to fulvestrant, a clinically approved ER-antagonist that reverses ER-mediated gene repression, induced a significant upregulation of KAI1 and inhibited cell proliferation as well as migration. In summary, we demonstrate for the first time that KAI1 is a target of ER-mediated gene-repression, and thus, it is downregulated in ER-positive breast cancer. Importantly, KAI1 might be reinducible by endocrine therapy with ER-antagonists in patients suffering from ER-positive breast cancer.     

Histopathologie und Stadieneinteilung des Endometriumkarzinoms und seiner Präkanzerosen

Two groups of endometrial adenocarcinoma can be distinguished, which differ in morphology, molecular biology and prognosis. Type I carcinomas are estrogen-dependent and have a favorable prognosis. The most frequent type of carcinoma in this group is endometrioid carcinoma. By molecular biology, PTEN mutations can be found in ca. 80% of the cases. Other frequent mutations affect the K-ras and the ß catenin gene. The most important prognostic factor is tumor stage. The precursor lesion is atypical hyperplasia of the endometrium which also reveals mutations of the PTEN gene. Type II carcinomas are not estrogen-dependent and by contrast are typically found in an atrophic endometrium. Classical examples of carcinomas in this group are serous and clear cell carcinoma. In contrast to type I carcinomas, these tumors are positive for p53 by immunohistochemistry. The most likely precursor lesion of invasive serous carcinoma is the endometrial intraepithelial carcinoma (EIC) which also reacts positively for p53. Growth fractions as determined by Ki67 immunostaining or MIB1 staining in type II carcinomas are large. Classification systems of endometrial hyperplasia have continued to change over the years, and this process is likely to continue. In the WHO classification simple and complex hyperplasia are distinguished as the two main groups, and as a third group atypical hyperplasia has been defined, since this form is biologically and prognostically different from the non-atypical forms. A new concept has recently been proposed. This concept of endometrial intraepithelial neoplasia (EIN) is characterized by better reproducibility and lower interobserver variability. The main idea of this new concept is the perception that atypical endometrial glands represent a monoclonal proliferation of cells with an increased risk of endometrial cancer, and thus need proper treatment.     

KAI1/CD82 protein expression in primary prostate cancer and in BPH associated with cancer

Current prognostic methods in primary prostate cancer cannot accurately identify patients with clinically significant disease at highest risk of developing metastases. This study examined KAI1/CD82 metastasis suppressor expression by quantitative immunohistochemical analysis of benign prostatic hyperplasia (BPH) and prostate cancer specimens. Altogether, prostate cancers exhibited significant KAI1 overexpression compared to BPH not associated with cancer (P = 0.022). Increased KAI1 expression in well and moderately differentiated cancers, above levels seen in BPH, with decreased expression in poorly differentiated cancers was observed. Interestingly, KAI1 expression in BPH associated with cancers was significantly higher than in BPH not associated with cancer (P = 0.009). Thus, KAI1 overexpression may restrain onset and early stage prostate cancer development, whilst its loss may predispose the patient to more aggressive cancer behaviour. Altered KAI1 expression in prostate cancers and BPH associated with cancer may have important diagnostic roles.