Alpha-methylacyl coenzyme A racemase immunoreactivity in partial atrophy of the prostate

Application and Pitfalls of Immunohistochemistry in Diagnosis of Challenging Genitourinary Cases

CONTEXT.—

Immunohistochemistry (IHC) has become increasingly important in the evaluation of pathologic conditions in the genitourinary (GU) organs. In addition to careful evaluation of hematoxylin-eosin sections and generation of a differential diagnosis, choosing the optimal panel of IHC markers becomes even more important when the biopsy material is very limited. The following summary of our experience supplemented with relevant literature review exemplifies how to use IHC to facilitate pathologic diagnosis in the GU system.

OBJECTIVE.—

To describe our experience with the most common immunohistochemical markers used in GU pathology.

DATA SOURCES.—

Institutional experience and literature search comprise our data sources.

CONCLUSIONS.—

Application of IHC provides enormous benefits to the interpretation of GU pathologic conditions, including benign and malignant lesions. However, both insufficient and excessive types of use of IHC, as well as incorrect interpretations in common and rare GU conditions, could present pitfalls in diagnosis.

Immunohistochemical Pitfalls in Genitourinary Pathology: 2018 Update

Immunohistochemistry may be a very useful adjunct to morphologic diagnosis in many areas of surgical pathology, including genitourinary pathology. In this review, we address common diagnostic dilemmas where immunophenotypic analysis may be utilized and we highlight pitfalls specific to each scenario. For prostate, we review the diagnosis of limited prostatic adenocarcinoma and the distinction of high-grade prostatic adenocarcinoma from urothelial carcinoma. We also cover markers of urothelial lineage in the diagnosis of metastatic carcinoma of unknown primary site. In the kidney, distinction of poorly differentiated renal cell carcinoma from urothelial carcinoma and epithelioid angiomyolipoma, adjuncts to the recognition of hereditary renal neoplasia, and the diagnosis of metastatic renal cell carcinoma are discussed. Finally, for testis we address distinction of germ cell tumors from sex cord-stromal tumors, as well as the diagnosis of metastatic germ cell tumors.

Variants of acinar adenocarcinoma of the prostate mimicking benign conditions

Histological variants of acinar adenocarcinoma of the prostate may be of significance due to difficulty in diagnosis or due to differences in prognosis compared to usual acinar adenocarcinoma. The 2016 World Health Organization classification of acinar adenocarcinoma includes four variants that are deceptively benign in histological appearance, such that a misdiagnosis of a benign condition may be made. These four variants are atrophic pattern adenocarcinoma, pseudohyperplastic adenocarcinoma, microcystic adenocarcinoma, and foamy gland adenocarcinoma. They differ from usual small acinar adenocarcinoma in architectural glandular structure and/or cytoplasmic and nuclear alterations. The variants are often admixed, in variable proportions, with usual small acinar adenocarcinoma that is often Gleason pattern 3 but may be high-grade pattern 4 in a minority of cases. Atrophic pattern adenocarcinoma can be identified in a sporadic setting or after radiation or hormonal therapy. This variant is characterized by cytoplasmic volume loss and can resemble benign glandular atrophy, an extremely common benign process in the prostate. The glands of pseudohyperplastic adenocarcinoma simulate usual epithelial hyperplasia, with gland complexity that is not typical of small acinar adenocarcinoma. These complex growth configurations include papillary infoldings, luminal undulations, and branching. Microcystic adenocarcinoma is characterized by cystic dilation of prostatic glands to a size that is much more commonly observed in cystic change in benign prostatic glands. Finally, the cells in foamy gland adenocarcinoma display cytoplasmic vacuolization and nuclear pyknosis, features that can found in benign glands and macrophages. Three of the four variants (atrophic, pseudohyperplastic, and microcystic) are assigned low-grade Gleason pattern 3. Of significance, foamy gland adenocarcinoma can be Gleason pattern 3 but can also be high-grade pattern 4 or 5. Diagnostic awareness of the existence of these deceptively benign-appearing variants of acinar adenocarcinoma is essential so that an accurate diagnosis of prostate cancer may be rendered.

Utility of ERG versus AMACR expression in diagnosis of minimal adenocarcinoma of the prostate in needle biopsy tissue

Adenocarcinoma of the prostate measuring <1 mm in needle core tissue can present a diagnostic challenge. The α-methylacyl-CoA racemase (AMACR) immunostain, a marker of neoplastic prostatic epithelial cells, may be used to evaluate these limited tumor cases, in needle biopsy, with a reported sensitivity ranging to a low of 80%. The use of the ERG immunostain in evaluating prostate cancer is becoming more common, but the utility of this marker in direct comparison with AMACR has not been examined. The purpose of our study was to investigate whether the ERG immunostain adds diagnostic value to AMACR expression in evaluating untreated prostate cancer foci measuring <1 mm in core needle biopsy. We identified 129 blocks from 113 patients with continuous tumor foci measuring <1 mm on core needle biopsy. ERG and AMACR immunostaining analyses were performed on serial sections from the blocks, and expression was assessed by intensity and proportion scores assigned to each stain. Sixty-five of the selected blocks from 63 patients retained tumor foci measuring <1 mm after obtaining deeper sections. Of these 65 tumor foci, 36 were positive for AMACR alone, 28 were positive for AMACR and ERG, and 1 was positive for ERG alone. AMACR had a sensitivity of 99%, and ERG had a sensitivity of 45%. Most cases displayed strong AMACR expression, and only 7 of 65 foci (11%) exhibited weak or negative AMACR expression. Of these 7 foci with weak or negative AMACR expression, only 2 foci were ERG positive. This is the first study to our knowledge that examines the diagnostic utility of ERG expression in comparison with AMACR expression in minimal usual acinar adenocarcinoma of the prostate in core needle biopsy. Our findings suggest that AMACR should be the first-line positive marker for confirmation of a diagnosis of minimal adenocarcinoma of the prostate, when needed. ERG immunohistochemistry is potentially indicated only in uncommon cases of minimal adenocarcinoma when AMACR staining is negative or weak, and in these cases ERG is informative in only a minority (29%) of cases. Evidence-based utilization of diagnostic markers, without their routine overutilization, such as ERG expression in minimal adenocarcinoma, that do not provide added diagnostic value in most cases, is an important principle in application of immunohistochemistry in this era of cost-consciousness.

Alpha methylacyl-CoA racemase (AMACR) in prostate adenocarcinomas from Japanese patients: is AMACR a "race"-dependent marker?

BACKGROUND

Alpha methylacyl-CoA racemase (AMACR) is a useful diagnostic marker for prostate adenocarcinoma. However, its usefulness has not been fully validated in Japanese patients. The aim of this study was to evaluate the diagnostic utility of AMACR in prostate needle biopsy examination in Japanese patients.

METHODS

A total of 119 prospective consecutive prostate needle biopsy specimens (680 cores) obtained from Japanese patients were examined. Sixty patients had adenocarcinoma (adenocarcinoma, 160 cores; benign, 204 cores), 14 patients had high-grade prostatic intraepithelial neoplasia (HGPIN; 19 cores), and 45 patients did not have any neoplastic lesions (297 cores). AMACR expression was scored semi-quantitatively as 0 (no expression), 1+ (partial and/or weak expression), or 2+ (strong, circumferential expression). The number of positively stained glands was counted.

RESULTS

2+ AMACR expression was observed in 70.1% of adenocarcinoma cases and in 52.6% of HGPIN cases. Of the adenocarcinoma cases showing 2+ AMACR expression, 34.8% demonstrated a heterogeneous expression pattern, with 1-75% of AMACR-positive glands. Three hundred eighty-five of the benign glands with an adenocarcinoma component showed 2+ AMACR expression (35 cases, 94 cores). 2+ AMACR expression was observed in 67 non-neoplastic benign glands (9 cases, 19 cores).

CONCLUSIONS

The sensitivity and specificity of AMACR for the diagnosis of prostate adenocarcinoma and benign glands in Japanese patients are lower than those previously reported in Western countries. Pathologists should be cautious while interpreting AMACR expression pattern in Japanese patients.

Pseudoneoplastic mimics of prostate and bladder carcinomas

CONTEXT

The differential diagnoses of prostatic carcinoma and bladder epithelial neoplasms include several histologic mimics that should be known to avoid misdiagnosis.

OBJECTIVE

To discuss pseudoneoplastic lesions of the prostate and bladder that could potentially be confused with prostatic carcinoma and bladder epithelial neoplasms, respectively, with specific focus on their distinguishing histopathologic features.

DATA SOURCES

Relevant published literature and authors' experience.

CONCLUSIONS

Pseudoneoplastic lesions in the prostate include those of prostatic epithelial origin, the most common being atrophy, adenosis (atypical adenomatous hyperplasia), basal cell hyperplasia, and crowded benign glands, as well as those of nonprostatic origin, such as seminal vesicle epithelium. Such lesions often mimic lower-grade prostatic adenocarcinoma, whereas others, such as clear cell cribriform hyperplasia and granulomatous prostatitis, for example, are in the differential diagnosis of Gleason adenocarcinoma, Gleason grade 4 or 5. Pseudoneoplastic lesions of the urinary bladder include lesions that could potentially be confused with urothelial carcinoma in situ, such as reactive urothelial atypia, and others, such as polypoid/papillary cystitis, where papillary urothelial neoplasms are the main differential diagnostic concern. Several lesions can mimic invasive urothelial carcinoma, including pseudocarcinomatous hyperplasia, von Brunn nests, and nephrogenic adenoma. Diagnostic awareness of the salient histomorphologic and relevant immunohistochemical features of these prostatic and urinary bladder pseudoneoplasms is critical to avoid rendering false-positive diagnoses of malignancy.

AMACR is not applicable as a diagnostic tool in hepatocellular carcinoma

Alpha-methylacyl coenzyme A racemase (AMACR or P504S) is a mitochondrial and peroxisomal protein present in a variety of human cells. Demonstration of increased expression is used diagnostically in prostatic adenocarcinoma. AMACR is also produced by normal hepatocytes and it has been postulated that the demonstration of AMACR expression or its pattern of distribution is useful in the diagnosis of hepatocellular carcinoma (HCC) (Jiang et al., Hum Pathol 2003;34, Guzman et al., Appl Immunohistochem Mol Morphol 2006;14, Li et al., J Exp Clin Cancer Res 2008;27). The aim of the present study was to evaluate whether immunohistochemical staining for AMACR can be used in a routine histopathologic setting. Immunohistochemical staining for AMACR was performed on paraffin-embedded tissue from livers resected for HCC during 1980-2006 at Rigshospitalet, Copenhagen, Denmark (n = 44). Tumor sections as well as surrounding non-neoplastic tissues were studied. In both tumor and non-tumor tissues, intracellular localization and staining pattern were assessed and the staining intensity of AMACR was graded. The fraction of stained tumor cells was not significantly different from that of stained non-tumor cells in the same patients (p = 0.97). A significantly lower staining intensity was observed in clear cell areas (p = 0.005), but the AMACR expression did not correlate with the HCC type and could not distinguish neoplastic from non-neoplastic liver cells. AMACR is not applicable as a tool in the histopathologic diagnosis of HCC.

Variability in diagnostic opinion among pathologists for single small atypical foci in prostate biopsies

Pathologists are increasingly exposed to prostate biopsies with small atypical foci, requiring differentiation between adenocarcinoma, atypical small acinar proliferation suspicious for malignancy, and a benign diagnosis. We studied the level of agreement for such atypical foci among experts in urologic pathology and all-round reference pathologists of the European Randomized Screening study of Prostate Cancer (ERSPC). For this purpose, we retrieved 20 prostate biopsies with small (most <1 mm) atypical foci. Hematoxylin and eosin-stained slides, including 10 immunostained slides were digitalized for virtual microscopy. The lesional area was not marked. Five experts and 7 ERSPC pathologists examined the cases. Multirater kappa statistics was applied to determine agreement and significant differences between experts and ERSPC pathologists. The kappa value of experts (0.39; confidence interval, 0.29-0.49) was significantly higher than that of ERSPC pathologists (0.21; confidence interval, 0.14-0.27). Full (100%) agreement was reached by the 5 experts for 7 of 20 biopsies. Experts and ERSPC pathologists rendered diagnoses ranging from benign to adenocarcinoma on the same biopsy in 5 and 9 biopsies, respectively. Most of these lesions comprised between 2 and 5 atypical glands. The experts diagnosed adenocarcinoma (49%) more often than the ERSPC pathologists (32%) (P<0.001). As agreement was particularly poor for foci comprising <6 glands, we would encourage pathologists to obtain intercollegial consultation of a specialized pathologist for these lesions before a carcinoma diagnosis, whereas clinicians may consider to perform staging biopsies before engaging on deferred or definite therapy.

Differentiation of a highly tumorigenic basal cell compartment in urothelial carcinoma

Highly tumorigenic cancer cell (HTC) populations have been identified for a variety of solid tumors and assigned stem cell properties. Strategies for identifying HTCs in solid tumors have been primarily empirical rather than rational, particularly in epithelial tumors, which are responsible for 80% of cancer deaths. We report evidence for a spatially restricted bladder epithelial (urothelial) differentiation program in primary urothelial cancers (UCs) and in UC xenografts. We identified a highly tumorigenic UC cell compartment that resembles benign urothelial stem cells (basal cells), co-expresses the 67-kDa laminin receptor and the basal cell-specific cytokeratin CK17, and lacks the carcinoembryonic antigen family member CEACAM6 (CD66c). This multipotent compartment resides at the tumor-stroma interface, is easily identified on histologic sections, and possesses most, if not all, of the engraftable tumor-forming ability in the parental xenograft. We analyzed differential expression of genes and pathways in basal-like cells versus more differentiated cells. Among these, we found significant enrichment of pathways comprising "hallmarks" of cancer, and pharmacologically targetable signaling pathways, including Janus kinase-signal transducer and activator of transcription, Notch, focal adhesion, mammalian target of rapamycin, epidermal growth factor receptor (erythroblastic leukemia viral oncogene homolog [ErbB]), and wingless-type MMTV integration site family (Wnt). The basal/HTC gene expression signature was essentially invisible within the context of nontumorigenic cell gene expression and overlapped significantly with genes driving progression and death in primary human UC. The spatially restricted epithelial differentiation program described here represents a conceptual advance in understanding cellular heterogeneity of carcinomas and identifies basal-like HTCs as attractive targets for cancer therapy.

Usefulness of cytokeratin 5/6 and AMACR applied as double sequential immunostains for diagnostic assessment of problematic prostate specimens

We evaluated the usefulness of double immunohistochemical staining for cytokeratin (CK)5/6 and alpha-methylacyl coenzyme A racemase (AMACR) applied sequentially on 1 slide by assessing 223 foci in 110 consecutive prostate specimens. Double-chromogen reaction was used to visualize the antibodies: brown for CK5/6 and red for AMACR. Staining was scored as diffuse, focal, or negative. To establish the diagnosis, CK5/6 and AMACR were correlated with the morphologic features. All cancers lacked CK5/6 staining (100% specificity). AMACR showed diffuse or focal positivity in cancer, high-grade prostatic intraepithelial neoplasia, and atypia in 96.8% (120/124), 85% (22/26), and 80% (16/20) of cases, respectively. In atypical cases, diagnosis was because of non-immunohistochemical staining reasons in 80% of cases. In adenosis (n = 14), AMACR was diffusely positive in 4 cases (29%). Double immunohistochemical staining for CK5/6 and AMACR is a simple assay to perform and may be used as an alternative to antibody cocktails for routine evaluation of problematic prostate specimens.