Molecular pathology of breast apocrine carcinomas: a protein expression signature specific for benign apocrine metaplasia

Breast cancer is a heterogeneous disease that encompasses a wide range of histopathological types including: invasive ductal carcinoma, lobular carcinoma, medullary carcinoma, mucinous carcinoma, tubular carcinoma, and apocrine carcinoma among others. Pure apocrine carcinomas represent about 0.5% of all invasive breast cancers according to the Danish Breast Cancer Cooperative Group Registry, and despite the fact that they are morphologically distinct from other breast lesions, there are at present no standard molecular criteria available for their diagnosis. In addition, the relationship between benign apocrine changes and breast carcinoma is unclear and has been a matter of discussion for many years. Recent proteome expression profiling studies of breast apocrine macrocysts, normal breast tissue, and breast tumours have identified specific apocrine biomarkers [15-hydroxyprostaglandin dehydrogenase (15-PGDH) and hydroxymethylglutaryl coenzyme A reductase (HMG-CoA reductase)] present in early and advanced apocrine lesions. These biomarkers in combination with proteins found to be characteristically upregulated in pure apocrine carcinomas (psoriasin, S100A9, and p53) provide a protein expression signature distinctive for benign apocrine metaplasias and apocrine cystic lesions. These studies have also presented compelling evidence for a direct link, through the expression of the prostaglandin degrading enzyme 15-PGDH, between early apocrine lesions and pure apocrine carcinomas. Moreover, specific antibodies against the components of the expression signature have identified precursor lesions in the linear histological progression to apocrine carcinoma. Finally, the identification of proteins that characterize the early stages of mammary apocrine differentiation such as 15-PGDH, HMG-CoA reductase, and cyclooxygenase 2 (COX-2) has opened a window of opportunity for pharmacological intervention, not only in a therapeutic manner but also in a chemopreventive setting. Here we review published and recent results in the context of the current state of research on breast apocrine cancer.     

15-prostaglandin dehydrogenase expression alone or in combination with ACSM1 defines a subgroup of the apocrine molecular subtype of breast carcinoma

Established histopathological criteria divide invasive breast carcinomas into defined groups. Ductal of no specific type and lobular are the two major subtypes accounting for around 75 and 15% of all cases, respectively. The remaining 10% include rarer types such as tubular, cribriform, mucinous, papillary, medullary, metaplastic, and apocrine breast carcinomas. Molecular profiling technologies, on the other hand, subdivide breast tumors into five subtypes, basal-like, luminal A, luminal B, normal breast tissue-like, and ERBB2-positive, that have different prognostic characteristics. An additional subclass termed "molecular apocrine" has recently been described, but these lesions did not exhibit all the histopathological features of classical invasive apocrine carcinomas (IACs). IACs make up 0.5-3% of the invasive ductal carcinomas, and despite the fact that they are morphologically distinct from other breast lesions, there are presently no standard molecular criteria available for their diagnosis and as a result no precise information as to their prognosis. Toward this goal our laboratories have embarked in a systematic proteomics endeavor aimed at identifying biomarkers that may characterize and subtype these lesions as well as targets that may lead to the development of novel targeted therapies and chemoprevention strategies. By comparing the protein expression profiles of apocrine macrocysts and non-malignant breast epithelial tissue we have previously reported the identification of a few proteins that are specifically expressed by benign apocrine lesions as well as by the few IACs that were available to us at the time. Here we reiterate our strategy to reveal apocrine cell markers and present novel data, based on the analysis of a considerably larger number of samples, establishing that IACs correspond to a distinct molecular subtype of breast carcinomas characterized by the expression of 15-prostaglandin dehydrogenase alone or in combination with a novel form of acyl-CoA synthetase medium-chain family member 1 (ACSM1). Moreover we show that 15-prostaglandin dehydrogenase is not expressed by other breast cancer types as determined by gel-based proteomics and immunohistochemistry analysis and that antibodies against this protein can identify IACs in an unbiased manner in a large breast cancer tissue microarray making them potentially useful as a diagnostic aid.     

Malignancy-associated changes in breast tissue detected by image cytometry.

In several tissues, nuclear differences have been described in normal-appearing cells from patients with invasive carcinomas compared to cases without invasive carcinoma, a phenomenon known as malignancy-associated changes (MACs). The aim of this study was to determine the presence of malignancy-associated changes in breast tissue. Image cytometry was performed on Feulgen stained tissue sections of patients with usual ductal hyperplasia with (n = 30) or without (n = 41) adjacent invasive breast carcinoma. Nuclear features of normal-appearing cells as well as of usual ductal hyperplastic cells were separately compared between the two groups. Many features of normal-appearing epithelial cells were significantly different between cases with and without invasive cancer. Significant differences were also found by measuring ductal hyperplastic nuclei instead of normal-appearing nuclei. Cases with or without cancer could be distinguished with a classification accuracy of 80% by discriminant analysis using 2 nuclear features derived from ductal hyperplastic cells. In conclusion, image cytometry on breast tissue sections shows that malignancy-associated changes can be found in normal as well as in usual ductal hyperplastic breast cells. This could be clinically relevant for the detection of occult breast cancer, for the prediction of risk in these lesions, and to monitor the effect of chemopreventive agents.     

Image cytometry in nonproliferative fibrocystic breast changes. Ploidy evaluation and epidemiologic study

OBJECTIVE: To determine the usefulness of image cytometry on fine needle aspirates from patients with fibrocystic changes (FCCs) to assess the subsequent risk of breast cancer. STUDY DESIGN: Thirty-five hundred archival cases with fine needle aspiration (FNA) biopsy were assessed to select nonproliferative FCCs of the breast (500 cases), also classified as type 1 (FCC I). DNA evaluation was analyzed by means of image cytometry on ductal epithelial cells and on apocrine metaplastic cells; 97 quantifications were performed. Cytometric variables investigated were: DNA ploidy, G0/G1 peak of diploid nuclei, S-phase fraction, 5cER, 2cDI and coefficient of variation. Two groups each with 15 years of follow-up were formed: Simple pathology (SP), fibrocystic changes alone; associated pathology (AP), FCCs plus breast cancer. Each was studied separately and compared. RESULTS: In SP cases the average ploidy was 2.2 for epithelial cells and 4.2 for apocrine cells. The proportion of G0G1 diploid nuclei was 100%. In the study of AP, the average ploidy was 2.2 for epithelial ductal cells and 4.1 for apocrine ones, for a slight increase in SPF. Ductal cells were diploid, while apocrine cells were tetraploid, with statistical significance of P < .05. For the epidemiologic study we calculated the proportion of patients with FCC I who developed cancer by referring to a historical cohort study, obtaining a relative risk of 0.7. CONCLUSION: Our results prove that DNA image cytometry applied on FNA cytology is a very useful, minimally invasive and reliable tool to determine higher activity and risk for development of breast cancer in FCC I and thus to establish the need for closer follow-up of these patients. In addition, apocrine metaplastic cells of the breast display a tetraploid DNA histogram, while the other karyometric variables remain in the range of normality.     

Substrate specificity of three prostaglandin dehydrogenases

Studies on the substrate specificity, kcat/Km, and effect of inhibitors on the human placental NADP-linked 15-hydroxyprostaglandin dehydrogenase (9-ketoprostaglandin reductase) indicate that it is very similar to a human brain carbonyl reductase which also possesses 9-ketoprostaglandin reductase activity. These observations led to a comparison of three apparently homogeneous 15-hydroxyprostaglandin dehydrogenases with varying amounts of 9-ketoprostaglandin reductase activity: an NAD- and an NADP-linked enzyme from human placenta and an NADP-linked enzyme from rabbit kidney. All three enzymes are carbonyl reductases for certain non-prostaglandin compounds. The placental NAD-linked enzyme, which has no 9-ketoprostaglandin reductase activity, is the most specific of the three. Although it has carbonyl reductase activity, a comparison of the Km and kcat/Km for prostaglandin and non-prostaglandin substrates of this enzyme suggests that its most likely function is as a 15-hydroxyprostaglandin dehydrogenase. The results of similar comparisons imply that the other two enzymes may function as less specific carbonyl reductases.     

乳腺内不可触及病灶的定位活检应用价值

目的:探讨乳腺内不可触及病灶(NPBL)的定位活检技术及其在乳腺癌早期诊断中的临床应用价值。方法:对彩超发现的4459个和钼靶发现的25个NPBL分别行麦默通旋切和钩丝定位活检,确定病灶的病理类型。结果:4459个NPBL中3196个病灶为乳腺腺病或伴纤维腺瘤样结节(71.7%),1198个为纤维腺瘤(26.9%),11个为分叶状肿瘤(0.2%),17个为导管内乳头状瘤(0.4%),9个为乳腺导管原位癌,5个为导管原位癌伴微浸润,23个为浸润性癌(恶性占0.8%)。25个钼靶发现的NPBL中乳腺腺病13例(52%),导管原位癌7例,导管原位癌伴微浸润2例,浸润性癌3例(恶性占48%)。结论:超声引导下麦默通和钼靶引导下钩丝定位切除可以对NPBL做出定性诊断,具备创伤小、手术时间短和定位精准等特点,对提高乳腺癌的早期诊断率、降低死亡率具有一定的临床应用价值。     

Steroid biochemistry and categorization of breast cyst fluid: relation to breast cancer risk

Patients bearing macrocysts of the breast are at higher risk of later developing cancer. The fluid filling the cysts (breast cysts fluid, BCF) contains unusual amounts of steroid conjugates, first androgen and estrogen sulfates. Measuring BCF cations (K⁺, Na⁺) allows categorization of cysts into two major subsets (type I and type II) that are associated with a different degree and/or turnover of apocrine metaplastic cells in the lining epithelium. Type I cysts (high K⁺/ Na⁺ ratio) accumulate huge amounts of dehydroepiandrosterone sulfate, estrone sulfate, androstane-3, 17β-diol glucuronide, androsterone glucuronide and contain more testosterone and dihydrotestosterone than type II. Conversely, type II cysts (low K⁺/Na⁺ ratio) contain more progesterone and pregnenolone. A cohort study was started in 1983 at the Cancer Prevention Center, Ravenna, Italy, with the aim of evaluating the relationships between the biochemistry of BCF and the incidence of breast cancer in women with gross cystic disease (GCD) of the breast. The bimodal distribution of the cationic pattern has been confirmed from data obtained in 798 patients aspirated. The risk of cyst relapse was significantly higher among women with type I cysts or with multiple cysts at presentation. Twelve incident cases of breast cancer have been diagnosed among women whose BCF was categorized. Eleven out of 12 cases had type I or multiple cysts. The cumulative incidence of breast cancer among patients bearing type I cysts was 2.5%. We conclude that women with GCD bearing type I cysts have an increased breast cancer risk when compared with the counterpart bearing type II cysts or the general population.     

Dormant Wnt-initiated mammary cancer can participate in reconstituting functional mammary glands

The minimal residual disease foci that beget breast cancer relapse after a period of disease dormancy remain uncharacterized despite their enormous clinical importance. To model dormant breast cancer in vivo, we employed a transgenic mouse model in which Wnt1-initiated mammary cancer is doxycycline dependent. After regression of Wnt-dependent cancers, subclinical disease lesions were propagated in vivo using classical tissue recombination techniques. Surprisingly, outgrowths derived from dormant malignant tissue reconstituted morphologically normal ductal trees in wild-type mammary fat pads. Whereas hyperplasia-derived outgrowths remained benign, outgrowths derived from dormant malignancy underwent a morphological transition suggesting single-step transformation following reactivation of Wnt signaling and rapidly yielded invasive mammary tumors. Remarkably, outgrowths derived from dormant malignancy could be serially propagated in vivo and retained the potential to undergo lobuloalveolar differentiation in response to hormones of pregnancy. Matching somatic H-Ras mutations shared by antecedent tumors and descendant mammary ductal outgrowths confirmed their clonal relatedness. Thus, propagation of epithelium that possesses a latent malignant growth program reveals impressive regenerative and developmental potential, supporting the notion that dormant mammary cancers harbor transformed mammary progenitor cells. Our results define an experimental paradigm for elucidating biological properties of dormant malignancy.     

DCE-MRI参数与肿瘤新生血管的相关性的研究

目的:研究DCE-MRI(dynamic contrast-enhanced magnetic resconance imaging,DCE-MRI)参数与肿瘤新生血管的相关性。方法:应用3.0T磁共振仪对124例乳腺肿瘤患者行DCE-MR检查,经手术病理证实恶性59例;良性65例。并计算血流动力学参数K~(trans)、K_(ep)、Ve以及ADC(apparent diffusion cofficient,ADC)值。运用Person检验分析磁共振各参数值与CD31、CD105表达的微血管密度(MVD)之间的相互关系,以及与细胞增殖Ki-67的相关性。结果:K~(trans)、K_(ep)以及ADC值在恶、良性病变、正常腺体组之间两两比较有统计学差异,K~(trans)、K_(ep)值在恶性病变组最高,高于正常组织、良性病变组(P0.05)。而Ve值正常腺体、良性病变以及正常腺体组与恶性病变组两两比较有统计学意义(P0.05),良性病变与恶性病变组比较无统计学差异(P0.05)。并且K~(trans)和K_(ep)值在浸润性导管癌和导管原位癌组明显高于不典型增生组(P0.001)。相反ADC值浸润性癌和导管原位癌低于不典型增生(P0.001)。而Ve值在各组间无统计学差异(P0.05)。另外CD105、Ki-67与磁共振参数K~(trans)、K_(ep)和ADC值之间具有相关性(P0.05,r=0.563,r=-0.566)。结论:DCE-MRI成像中K~(trans)、K_(ep)和ADC值可以定量评估乳腺癌微血管密度。     

A novel histology-directed strategy for MALDI-MS tissue profiling that improves throughput and cellular specificity in human breast cancer

We describe a novel tissue profiling strategy that improves the cellular specificity and analysis throughput of protein profiles obtained by direct MALDI analysis. The new approach integrates the cellular specificity of histology, the accuracy and reproducibility of robotic liquid dispensing, and the speed and objectivity of automated spectra acquisition. Traditional methodologies for preparing and analyzing tissue samples rely heavily on manual procedures, which for various reasons discussed, restrict cellular specificity and sample throughput. Here, a robotic spotter deposits micron-sized droplets of matrix precisely onto foci of normal mammary epithelium, ductal carcinoma in situ, invasive mammary cancer, and peritumoral stroma selected by a pathologist from high resolution histological images of sectioned human breast cancer samples. The location of each matrix spot was then determined and uploaded into the instrument to facilitate automated profile acquisition by MALDI-TOF. In the example shown, the different lesions were clearly differentiated using mass profiling. Further, the workflow permits a visual projection of any information produced from the profile analyses directly on the histological image for a unique combination of proteomic and histological assessment of sample regions. The higher performance characteristics offered by the new workflow promises to be a significant advancement toward the next generation of tissue profiling studies.     

Cohort study of association of risk of breast cancer with cyst type in women with gross cystic disease of the breast.

OBJECTIVE: To assess correlation between type of breast cyst and risk of breast cancer in women with gross cystic disease of the breast. DESIGN: Cohort study of women with breast cysts aspirated between 1983 and 1993 who were followed up until December 1994 for occurrence of breast cancer. SETTING: Major cancer prevention centre. SUBJECTS: 802 women with aspirated breast cysts. MAIN OUTCOME MEASURES: Type of breast cyst based on cationic content of cyst fluid: type I (potassium:sodium ratio > 1.5), type II (potassium:sodium ratio < 1.5), or mixed (both types). Subsequent occurrence and type of breast cancer. RESULTS: After median follow up of six years (range 2-12 years) 15 cases of invasive breast cancer and two ductal carcinomas in situ were diagnosed in the cohort: 12 invasive cancers (and two carcinomas in situ) among the 417 women with type I cysts, two cancers among the 325 women with type II cysts, and one among the 60 women with mixed cysts. The incidence of breast cancer in women with type I cysts was significantly higher than that in women with type II cysts (relative risk 4.62 (95% confidence interval 1.26 to 29.7)). These results were confirmed after adjustment for several risk factors for breast cancer (relative risk 4.24 (1.12 to 27.5)). CONCLUSIONS: The increased risk of breast cancer of women with breast cysts seems to be concentrated among women with type I breast cysts.     

Fine needle aspiration cytology of mammary hamartoma: a review of nine cases with histological correlation

Mammary hamartoma is a breast lesion rarely reported by fine-needle aspiration cytology (FNAC). We report on our experience of FNAC in nine cases confirmed by biopsy. We searched hospital case files for mammary hamartoma or similar lesions (fibrolipomas, lipomas, fibromas, etc.), and cases included were only those in which both FNAC and a histopathological study had been performed. The cytological features that were analysed included epithelial components, mesenchymal fragments and isolated cells dispersed in the background. The patients ranged in age from 25 to 58 years (mean 40 years), and the lesions were predominantly in the right breast and upper outer quadrant. The duration varied from 1 to 20 years. Mammographic features were characteristic revealing well-circumscribed masses of heterogeneous radiodensity and by ultrasonography were hypoechoic without calcification. Grossly, these lesions were oval to round, well-demarcated masses, ranging in diameter from 10 to 80 mm. The tumours were firm, rubbery and white, consisting largely of dense fibroconnective tissue with variable amounts of adipose tissue and glandular elements. Cytological samples showed two components, epithelial and mesenchymal. The cellularity was variable and was composed of lobular cells forming acini, ductal cells, occasional apocrine and foamy cells; myoepithelial cells and isolated naked nuclei were also observed. Adipose tissue and dense fibrous tissue were observed, occasionally with epithelial cells attached, and this finding was an important feature for diagnosis. We considered that the cytological findings could help to diagnose mammary hamartoma, FNAC making a rapid and very important technique for the diagnosis of this pathology.     

Selective release of microRNA species from normal and malignant mammary epithelial cells

MicroRNAs (miRNAs) in body fluids are candidate diagnostics for a variety of conditions and diseases, including breast cancer. One premise for using extracellular miRNAs to diagnose disease is the notion that the abundance of the miRNAs in body fluids reflects their abundance in the abnormal cells causing the disease. As a result, the search for such diagnostics in body fluids has focused on miRNAs that are abundant in the cells of origin. Here we report that released miRNAs do not necessarily reflect the abundance of miRNA in the cell of origin. We find that release of miRNAs from cells into blood, milk and ductal fluids is selective and that the selection of released miRNAs may correlate with malignancy. In particular, the bulk of miR-451 and miR-1246 produced by malignant mammary epithelial cells was released, but the majority of these miRNAs produced by non-malignant mammary epithelial cells was retained. Our findings suggest the existence of a cellular selection mechanism for miRNA release and indicate that the extracellular and cellular miRNA profiles differ. This selective release of miRNAs is an important consideration for the identification of circulating miRNAs as biomarkers of disease.     

Diagnosing benign and malignant lesions in breast tissue sections by using IR-microspectroscopy

The collection of IR spectra through microscope optics and the visualization of the IR data by IR imaging represent a visualization approach, which uses infrared spectral features as a native intrinsic contrast mechanism. To illustrate the potential of this spectroscopic methodology in breast cancer research, we have acquired IR-microspectroscopic data from benign and malignant lesions in breast tissue sections by point microscopy with spot sizes of 30-40 microm. Four classes of distinct breast tissue spectra were defined and stored in the data base: fibroadenoma (a total of 1175 spectra from 14 patients), ductal carcinoma in situ (a total of 1349 spectra from 8 patients), connective tissue (a total of 464 spectra), and adipose tissue (a total of 146 spectra). Artifical neural network analysis, a supervised pattern recognition method, was used to develop an automated classifier to separate the four classes. After training the artifical neural network classifier, infrared spectra of independent external validation data sets ("unknown spectra") were analyzed. In this way, all spectra (a total of 386) taken from micro areas inside the epithelium of fibroadenomas from 4 patients were correctly classified. Out of the 421 spectra taken from micro areas of the in situ component of invasive ductal carcinomas of 3 patients, 93% were correctly identified. Based on these results, the potential of the IR-microspectroscopic approach for diagnosing breast tissue lesions is discussed.     

Prostaglandin dehydrogenase activity of purified rat liver 3 alpha-hydroxysteroid dehydrogenase

Homogeneous 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSD) from rat liver cytosol displays 9, 11, and 15-hydroxyprostaglandin dehydrogenase activity. Using [14C]-PGF2 alpha as substrate the products of this reaction were separated by TLC and identified by autoradiography as PGE2 and PGB2. The purified enzyme catalyzes this reaction at a rate 200 times faster than cytosol. This corresponds to the rate enhancement observed when the enzyme is purified from cytosol using androsterone (a 3 alpha-hydroxysteroid) as substrate and suggests that it may represent a major 9-hydroxyprostaglandin dehydrogenase in this tissue. Although the 3 alpha-HSD has many properties in common with the 9-hydroxyprostaglandin dehydrogenase of rat kidney, rat kidney contains no protein that is immunodetectable with polyclonal antibody raised against the purified 3 alpha-HSD.     

Mammary mucinous carcinoma with marked cytoplasmic hyalinization. A report of 2 cases with emphasis on fine needle aspiration cytologic findings

BACKGROUND: Cytoplasmic eosinophilia in breast tumors is due mainly to abundance of secretory granules, lysosomes and/or mitochondria. Diffuse cytoplasmic hyalinization caused by intermediate filaments has not been described before. CASES: Two cases of pure mammary mucinous carcinoma occurred with marked cytoplasmic hyalinization among 556 wide excision/mastectomy specimens of mammary ductal carcinoma, either in situ or invasive, encountered at Pamela Youde Nethersole Eastern Hospital, Hong Kong, during the period from 1994 to the end of 2001. Preoperative fine needle aspiration cytology was available in 1 case, showing cohesive clusters and micropapillae of tumor cells in abundant background mucin. The tumor cells had low mitotic activity and possessed round to oval nuclei, solitary macronucleoli; ample, eosinophilic cytoplasm and discrete cell borders. Cytoplasmic granularity, intracytoplasmic vacuoles or "cometlike" cells were not found. Histologic examination of the surgical specimens in both cases revealed pure mucinous carcinoma with diffuse and marked cytoplasmic hyalinization. There was no evidence of peritumoral lymphovascular permeation or regional lymph node metastasis. Ultrastructural examination showed minimal secretory activity, with abundant, loose aggregates of intermediate filaments in the cytoplasm. There was a relative paucity of other organelles. CONCLUSION: Diffuse cytoplasmic hyalinization is a peculiar morphologic change in mammary ductal carcinoma and apparently unique to pure mucinous carcinoma. Recognition of this phenomenon may help to avoid misdiagnosis of other types of ductal carcinoma with cytoplasmic eosinophilia, such as apocrine carcinoma and ductal carcinoma with neuroendocrine differentiation, which sometimes are also associated with pools of extracellular mucin.     

Non-enzymatic,Serum-free Tissue Culture of Pre-invasive Breast Lesions for Spontaneous Generation of Mammospheres

Breast ductal carcinoma in situ (DCIS), by definition, is proliferation of neoplastic epithelial cells within the confines of the breast duct, without breaching the collagenous basement membrane. While DCIS is a non-obligate precursor to invasive breast cancers, the molecular mechanisms and cell populations that permit progression to invasive cancer are not fully known. To determine if progenitor cells capable of invasion existed within the DCIS cell population, we developed a methodology for collecting and culturing sterile human breast tissue at the time of surgery, without enzymatic disruption of tissue.Sterile breast tissue containing ductal segments is harvested from surgically excised breast tissue following routine pathological examination. Tissue containing DCIS is placed in nutrient rich, antibiotic-containing, serum free medium, and transported to the tissue culture laboratory. The breast tissue is further dissected to isolate the calcified areas. Multiple breast tissue pieces (organoids) are placed in a minimal volume of serum free medium in a flask with a removable lid and cultured in a humidified CO₂ incubator. Epithelial and fibroblast cell populations emerge from the organoid after 10 - 14 days. Mammospheres spontaneously form on and around the epithelial cell monolayer. Specific cell populations can be harvested directly from the flask without disrupting neighboring cells. Our non-enzymatic tissue culture system reliably reveals cytogenetically abnormal, invasive progenitor cells from fresh human DCIS lesions.     

Characterization of a monoclonal antibody for human aldo-keto reductase AKR1C3 (type 2 3alpha-hydroxysteroid dehydrogenase/type 5 17beta-hydroxysteroid dehydrogenase); immunohistochemical detection in breast and prostate

Human aldo-keto reductase AKR1C3 (type 2 3alpha-hydroxysteroid dehydrogenase/type 5 17beta-hydroxysteroid dehydrogenase) catalyzes the reduction of Delta(4)-androstene-3,17-dione to yield testosterone, the reduction of 5alpha-dihydrotestosterone to yield 3alpha- and 3beta-androstanediol, and the reduction of estrone to yield 17beta-estradiol. Relatively, high mRNA expression of AKR1C3 was found in human prostate and mammary gland where it is implicated in regulating ligand access to the androgen and estrogen receptor, respectively. AKR1C3 shares high sequence identity >86% with related plastic human 20alpha-hydroxysteroid dehydrogenases (AKR1C1), type 3 3alpha-hydroxysteroid dehydrogenase (AKR1C2) and type 1 3alpha-hydroxysteroid dehydrogenase (AKR1C4), and reagents are urgently needed to discriminate between these enzymes at the mRNA, protein and functional level. We describe the characterization of a high-titer isoform specific monoclonal antibody (Ab) for AKR1C3. It does not cross react with human AKR1C1, AKR1C2 or AKR1C4, human aldehyde reductase AKR1A1 or rat 3alpha-hydroxysteroid dehydrogenase (AKR1C9) on immunoblot analysis. The monoclonal Ab can be used to detect AKR1C3 expression by immunohistochemistry in sections of paraffin-embedded mammary gland and prostate. In the breast enzyme staining was detected in ductal carcinoma in situ where the cancerous cells were strongly immunoreactive. In normal prostate immunoreactivity was limited to stromal cells with only faint staining in the epithelial cells. In adenocarcinoma of the prostate elevated staining was observed in the endothelial cells and carcinoma cells. The reagent thus has utility to access the localized expression of AKR1C3 in hormonal dependent malignancies of the breast and prostate.