The Utility of Pax-2 and Renal Cell Carcinoma Marker Immunohistochemistry in Distinguishing Papillary Renal Cell Carcinoma From Nonrenal Cell Neoplasms With Papillary Features

Metastatic Renal Cell Carcinoma to Pancreas: Case Series and Review of the Literature

Metastasis to the pancreas represents a small proportion of all pancreatic malignancies. Among primary tumors that metastasize to the pancreas, renal cell carcinoma (RCC) is one of the most common causes of metastatic pancreatic lesions. We herein report a case series of three patients with pancreatic metastasis from RCC. The first is a 54-year-old male with a history of left nephrectomy for RCC, in whom an isthmic pancreatic mass suggestive of a neuroendocrine lesion was found during oncological follow-up. Endoscopic ultrasound (EUS)-guided fine needle biopsy (FNB) identified pancreatic metastasis of RCC and the patient was referred for surgery. The second case is a 61-year-old male, hypertensive, diabetic, with left nephrectomy for RCC six years previously, who complained of weight loss and was found with a hyperenhancing mass in the head of the pancreas and a lesion with a similar pattern in the gallbladder. EUS-FNB from the pancreas proved to be a metastatic pancreatic lesion. Cholecystectomy and treatment with tyrosine kinase inhibitors were recommended. The third case is a 68-year-old dialysis patient referred for evaluation of a pancreatic mass, also confirmed by EUS-FNB, who was started on sunitinib treatment. We report a literature summary on epidemiology and clinical features, diagnosis and differential diagnosis and treatment and outcomes in pancreatic metastasis of RCC.

Metastatic Renal Cell Carcinoma to Pancreas: Case Series and Review of the Literature

Metastasis to the pancreas represents a small proportion of all pancreatic malignancies. Among primary tumors that metastasize to the pancreas, renal cell carcinoma (RCC) is one of the most common causes of metastatic pancreatic lesions. We herein report a case series of three patients with pancreatic metastasis from RCC. The first is a 54-year-old male with a history of left nephrectomy for RCC, in whom an isthmic pancreatic mass suggestive of a neuroendocrine lesion was found during oncological follow-up. Endoscopic ultrasound (EUS)-guided fine needle biopsy (FNB) identified pancreatic metastasis of RCC and the patient was referred for surgery. The second case is a 61-year-old male, hypertensive, diabetic, with left nephrectomy for RCC six years previously, who complained of weight loss and was found with a hyperenhancing mass in the head of the pancreas and a lesion with a similar pattern in the gallbladder. EUS-FNB from the pancreas proved to be a metastatic pancreatic lesion. Cholecystectomy and treatment with tyrosine kinase inhibitors were recommended. The third case is a 68-year-old dialysis patient referred for evaluation of a pancreatic mass, also confirmed by EUS-FNB, who was started on sunitinib treatment. We report a literature summary on epidemiology and clinical features, diagnosis and differential diagnosis and treatment and outcomes in pancreatic metastasis of RCC.

Contemporary Clinical Definitions, Differential Diagnosis, and Novel Predictive Tools for Renal Cell Carcinoma

Despite significant progress regarding clinical detection/imaging evaluation modalities and genetic/molecular characterization of pathogenesis, advanced renal cell carcinoma (RCC) remains an incurable disease and overall RCC mortality has been steadily rising for decades. Concomitantly, clinical definitions have been greatly nuanced and refined. RCCs are currently viewed as a heterogeneous series of cancers, with the same anatomical origin, but fundamentally different metabolisms and clinical behaviors. Thus, RCC pathological diagnosis/subtyping guidelines have become increasingly intricate and cumbersome, routinely requiring ancillary studies, mainly immunohistochemistry. Meanwhile, RCC-associated-antigen targeted systemic therapy has been greatly diversified and emerging, novel clinical applications for RCC immunotherapy have already reported significant survival benefits, at least in the adjuvant setting. Even so, systemically disseminated RCCs still associate very poor clinical outcomes, with currently available therapeutic modalities only being able to prolong survival. In lack of a definitive cure for advanced RCCs, integration of the amounting scientific knowledge regarding RCC pathogenesis into RCC clinical management has been paramount for improving patient outcomes. The current review aims to offer an integrative perspective regarding contemporary RCC clinical definitions, proper RCC clinical work-up at initial diagnosis (semiology and multimodal imaging), RCC pathological evaluation, differential diagnosis/subtyping protocols, and novel clinical tools for RCC screening, risk stratification and therapeutic response prediction.

Carcinoma of Unknown Primary Origin: Application of Immunohistochemistry With Emphasis to Different Cytokeratin 7 and 20 Staining Patterns

BACKGROUND

Although the primary origin of some carcinomas may be obscure to clinicians, its identification is crucial as it affects prognosis and treatment (especially novel targeted therapies). Immunohistochemistry (IHC) may be helpful in identifying the primary origin of carcinomas. This retrospective survey aimed to evaluate the frequency and accuracy of each IHC marker used to determine the origin of carcinomas.

METHODS

The review of pathology department archives revealed 307 cases of cancer of unknown primary origin (CUP) between 2015 and 2020, which were accessible in the department archives. Demographic information, site of biopsy, clinical and pathologic diagnoses, and IHC results of the patients were collected.

RESULTS

The patients included 157 (51.15%) men and 150 (48.85%) women. The age of the patients ranged from 14 to 92 years, including 106 (34.5%) expired cases. In 27% of cases, the primary origin of carcinoma remained unknown. The agreement between pathologic and clinical diagnoses was 59%. The most common pattern of cytokeratin (CK) expression in CUP was CK7+/CK20- (55.3%), followed by CK7-/CK20- (19%), CK7+/CK20+ (15%), and CK7-/CK20+ (10.7%), respectively.

CONCLUSION

The IHC analysis may improve the diagnosis of CUPs. However, the origin of some cases remains unknown despite an IHC analysis, thereby necessitating the use of more diagnostic procedures or gene expression studies for reaching a definitive diagnosis.

Serous Carcinoma of the Endometrium with Mesonephric-Like Differentiation Initially Misdiagnosed as Uterine Mesonephric-Like Adenocarcinoma: A Case Report with Emphasis on the Immunostaining and the Identification of Splice Site TP53 Mutation

We present herein a rare case of uterine serous carcinoma with mesonephric-like differentiation (SC-MLD) initially misdiagnosed as mesonephric-like adenocarcinoma (MLA). A 51-year-old woman underwent total hysterectomy for a uterine tumor. Histologically, the tumor exhibited various architectures, including papillary, glandular, tubular, cribriform, and cystic. On the basis of this architectural diversity accompanied by intraluminal eosinophilic secretions and intermediate-grade nuclear atypia, the initial diagnosis was MLA. However, the tumor was diffusely and strongly positive for the expression of p16 and negative for the expression of GATA-binding protein 3 (GATA3). Furthermore, we identified a pathogenic tumor protein 53 (TP53) mutation affecting an acceptor splice site in intron 9, despite a wild-type p53 immunostaining pattern. The observations of diffuse and strong p16 expression, lack of GATA3 expression, pathogenic TP53 mutation, and wild-type Kirsten rat sarcoma viral oncogene homolog indicate that this tumor was not an MLA but an SC-MLD. Both uterine SC and MLA can exhibit various histological growth patterns. Our comprehensive clinicopathological and molecular analyses can serve to improve the understanding of this rare condition and help pathologists in making an accurate diagnosis.

Congenital Anomalies of the Kidney and Urinary Tract and Adulthood risk of Urinary Tract Cancer

Introduction

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common kidney diseases in childhood. Alterations in genes governing nephrogenesis may cause CAKUT, and in some cases may contribute to development of urinary tract (UT) tumors later in life. We aimed to assess the association between CAKUT and UT cancer in adulthood.

Methods

We conducted a population-based historical cohort study encompassing 1,510,042 recruits to the Israeli army between 1967 and 1997. CAKUT exposure was determined by army medical coding of CAKUT in childhood. Incidence of UT cancer (kidney, ureter, or bladder) was available through record linkage with the Israeli Cancer Registry. Recruits were followed from the prerecruitment assessment until cancer diagnosis, death, or study termination, in 2012. Cox proportional hazards models were constructed to estimate the hazard ratios (HRs) for UT cancer in participants with vs. without CAKUT.

Results

During a mean follow-up of 30.4 years, 2959 participants (2573 men and 386 women) developed UT cancer. Men with CAKUT exhibited an increased risk of UT cancer compared with men without CAKUT, yielding an adjusted HR of 1.98 (95% confidence interval [CI] 1.03-3.82). Among women CAKUT was associated with a HR of 5.88 (95% CI 2.19-15.76). Notably, upon stratification according to age of cancer diagnosis, the association between CAKUT and UT cancer was statistically significant only before 45 years of age in women and only after 45 years of age in men.

Conclusion

CAKUT is associated with a significantly increased risk of UT cancer, although the incidence and absolute risk remained quite low.

Paired box 2 promotes progression of endometrial cancer via regulating cell cycle pathway

Background: Human paired box 2 (PAX2) plays a key role in cell fate, early patterning and organogenesis.

Methods: We investigated the function of PAX2 on the biological behavior of endometrial cancer in vitro and in vivo and to explore the regulation mechanism, stable knocking-down and over-expression PAX2 endometrial cancer cell lines were established. CCK-8 and transwell assays were applied to determine proliferation, invasion and migration ability. Cell cycle distribution was analyzed by flow cytometry. Affymetrix GeneChip® human Exon 1.0 ST arrays was used to screen the downstream target genes of PAX2.

Results: PAX2 significantly enhanced proliferation and invasiveness. In addition, PAX2 influenced the expression of cyclin-dependent kinase 1(CDK1), which play pivotal roles in cell cycle pathway. When CDK1 was knocked down, and the cell proliferation promotion role of PAX2 was attenuated dramatically to a level comparable with the control groups.

Conclusions: PAX2, though influencing the expression of CDK1, promotes the proliferation, enhances the mobility of endometrial cancer cells, thus exerts an important role in the carcinogenesis of endometrial cancer. PAX2 may be a potential therapeutic target for endometrial cancer.

Emerging entities in renal cell neoplasia: thyroid-like follicular renal cell carcinoma and multifocal oncocytoma-like tumours associated with oncocytosis

The list of accepted entities of renal cell neoplasia has burgeoned since the turn of the century through recognition of rare tumour types and the discovery of genetic mutations driving renal neoplasia syndromes. This growth has not finished and in this report we present examples of each of these types which were not included in the 2016 World Health Organization classification of renal neoplasia, but are candidates for inclusion in the next edition of the classification. Thyroid-like follicular renal cell carcinoma is a rare tumour type with a distinctive microscopic appearance resembling follicles of the thyroid gland. Thirty-nine cases have been described and the findings have been reasonably consistent. Oncocytoma-like tumours associated with oncocytosis arise as a result of somatic mutations in the mitochondrial genome. The differential diagnosis is mainly with the renal lesions of the Birt-Hogg-Dubé syndrome, which is the result of germline mutations in the folliculin gene. Patients with oncocytoma-like tumours associated with oncocytosis are at great risk of developing renal failure as the proliferating lesions replace the renal parenchyma. Oncocytoma-like tumours have never been found to metastasise.

Metastatic neoplasms to the thyroid diagnosed by fine-needle aspiration/core needle biopsy: Clinicopathologic and cytomorphologic correlation

BACKGROUND

Although thyroid fine-needle aspiration (FNA) and core needle biopsy (CNB) are commonly utilized modalities in the evaluation of thyroid nodules, metastatic tumors to the thyroid are only rarely encountered. We aspired to determine the incidence and primary origin of metastases to the thyroid at our institution and to examine their clinicopathologic and cytomorphologic features.

MATERIALS AND METHODS

A search of our database was undertaken to review all thyroid FNA and/or CNB examined between January 2004 and December 2013.

RESULTS

During our 10 year study period, 7497 patients underwent 13,182 FNA and/or CNB. Four hundred sixty one (6%) patients were diagnosed with neoplasms. Only five (1.1%) were found to have metastatic tumors to the thyroid involving three females and two males. Two were diagnosed by FNA, one by CNB, and two by both FNA and CNB, with rapid on-site evaluation (ROSE) employed in all cases. The primary malignancies in the five cases were pulmonary and nasopharyngeal squamous cell carcinomas, renal cell carcinoma, pancreatic adenocarcinoma, and olfactory neuroblastoma. The cytomorphologic features of these metastases to the thyroid aided in their distinction from primary thyroid carcinoma. Two of these metastases, a renal cell carcinoma and pancreatic adenocarcinoma, were the first clinical manifestations of cancer.

CONCLUSION

Metastases to the thyroid diagnosed by FNA and/or CNB are exceedingly rare in our institution, comprising only 0.04% of total FNA/CNB and only 1.1% of all thyroid neoplasms. We report the first known case of metastatic olfactory neuroblastoma to the thyroid diagnosed by aspiration cytology. In addition, an occult primary may present as a thyroid mass on FNA or CNB as occurred with two of our cases. FNA/CNB proved to be highly effective in the diagnosis of metastases to the thyroid, with ROSE proving valuable in assuring specimen adequacy. Thyroid FNA and CNB demonstrated great utility in the setting of metastatic disease, obviating the need for more invasive procedures.

PAX2 and PAX8 reliably distinguishes ovarian serous tumors from mucinous tumors

Ovarian cancer is the leading cause of cancer-related death in gynecologic malignancies and consists of different histologic types. Histopathologic examination and accurate subtype diagnosis has become increasingly important in guiding patient management and, as such, is the most important currently available ovarian carcinoma "biomarker." In this study, we examined the expression of PAX2 and PAX8 by immunohistochemistry in 58 cases of ovarian serous tumors and 68 cases of ovarian mucinous tumors. The results demonstrated that PAX2 and PAX8 were detected in 100% (30/30) and 77% (23/30) of serous cystadenomas, 100% (16/16) and 94% (15/16) of borderline serous cystadenomas, and 100% (12/12) and 83% (10/12) of serous carcinomas, respectively. However, PAX2 and PAX8 were detected in only 0% (0/29) and 0% (0/29) of mucinous cystadenoma, 4% (1/24) and 4% (1/24) of borderline mucinous cystadenoma, and 0% (0/15) and 7% (1/15) of mucinous carcinoma, respectively. Further, there is a linear correlation between PAX2 and PAX8 (R=0.745; P<0.0001). Overall, our data indicated that PAX2 correlated with PAX8, and these 2 proteins differentially expressed in ovarian serous tumors and ovarian mucinous tumors. Thus, PAX2 and PAX8 are useful biomarker in the differential diagnosis of ovarian serous and mucinous tumors.

The ventricular system and choroid plexus as a primary site for renal cell carcinoma metastasis

BACKGROUND

Brain metastases (BM) are the most common intracranial tumours amongst adults. Ten to 40 % of patients with cancer will develop BM. In this study, we observed a high affinity of renal cell carcinoma (RCC) to the ventricular system, with close association to the choroid plexus.

METHODS

This is a retrospective study evaluating data of our prospectively maintained brain tumour database, focusing on consecutive BM patients, who were treated at our center between March 2003 and December 2011. Data collected included primary pathologies, anatomical distribution of the brain metastasis according to neuroimaging, and treatment modalities.

RESULTS

We identified 614 patients with BM, of whom 24 (3.9 %) were diagnosed with RCC, harboring 33 lesions. Nine of the 24 patients (37.5 %) presented with an intraventricular location (10 of 33 RCC BM lesions). Of the remaining 590 patients with non-RCC pathologies, five patients (0.8 %) were diagnosed with intraventricular lesions (p < 0.0001).

CONCLUSION

In this unselected, consecutive treated BM patient cohort we observed a high affinity of RCC BM to the ventricular system with close association to the choroid plexus. The reason for this affinity is unknown. Surgical approaches for resection of these lesions should be planned to include early control on the vascular supply from the choroidal vessels.

Renal tumors: diagnostic and prognostic biomarkers

The International Society of Urological Pathology convened a consensus conference on renal cancer, preceded by an online survey, to address issues relating to the diagnosis and reporting of renal neoplasia. In this report, the role of biomarkers in the diagnosis and assessment of prognosis of renal tumors is addressed. In particular we focused upon the use of immunohistochemical markers and the approach to specific differential diagnostic scenarios. We enquired whether cytogenetic and molecular tools were applied in practice and asked for views on the perceived prognostic role of biomarkers. Both the survey and conference voting results demonstrated a high degree of consensus in participants' responses regarding prognostic/predictive markers and molecular techniques, whereas it was apparent that biomarkers for these purposes remained outside the diagnostic realm pending clinical validation. Although no individual antibody or panel of antibodies reached consensus for classifying renal tumors, or for confirming renal metastatic disease, it was noted from the online survey that 87% of respondents used immunohistochemistry to subtype renal tumors sometimes or occasionally, and a majority (87%) used immunohistochemical markers (Pax 2 or Pax 8, renal cell carcinoma [RCC] marker, panel of pan-CK, CK7, vimentin, and CD10) in confirming the diagnosis of metastatic RCC. There was consensus that immunohistochemistry should be used for histologic subtyping and applied before reaching a diagnosis of unclassified RCC. At the conference, there was consensus that TFE3 and TFEB analysis ought to be requested when RCC was diagnosed in a young patient or when histologic appearances were suggestive of the translocation subtype; whereas Pax 2 and/or Pax 8 were considered to be the most useful markers in the diagnosis of a renal primary.

Histologic variations and immunohistochemical features of metastatic clear cell renal cell carcinoma

BACKGROUND

Due to advancements in treatment of metastatic and advanced renal cell carcinoma (RCC), it has become increasingly important to diagnose metastatic RCC and the specific subtype. In this study, we investigated the diverse histologic features of metastatic clear cell renal cell carcinoma (CCRCC) cases in comparison with corresponding primary lesions.

METHODS

We identified 119 metastatic CCRCC cases from 81 corresponding primary lesions diagnosed between 1995 and 2010 and evaluated the diverse histologic and immunohistochemical features of these lesions.

RESULTS

A total of 44 primary lesions (54.3%) had a non-clear cell component in addition to a typical clear cell component. Of the 119 metastatic lesions, 63 lesions (52.9%) contained a non-clear cell component, and 29 metastatic lesions were composed of a non-clear cell component only. Rhabdoid features were the most frequent non-clear cell histology among the metastatic lesions. Metastatic CCRCCs mainly showed positive CD10 and epithelial membrane antigen staining and negative cytokeratin 7 staining.

CONCLUSIONS

Metastatic CCRCC commonly showed a variety of histologic features. If there is a difficulty to diagnose metastatic CCRCC due to a variety of histologic features or small biopsy specimen, histologic review of the primary lesion and immunohistochemical analysis can help determine the correct diagnosis.

Primary carcinoma of renal calyx

Renal calyx carcinoma (RCXC) may mimic collecting duct carcinoma (CDC) or urothelial carcinoma (UC) of the renal pelvis. RCXC is distinguished from CDC and UC of the renal pelvis as having the tumor epicenter in the renal calyx, with limited involvement of the surrounding renal pelvis surface urothelium. In this study, we summarize our experience with this entity. Ten cases of RCXC, including 9 cases with urothelial differentiation (RCXC-UC) and 1 case with salivary gland-type differentiation (RCXC-SC), were identified. Ten consecutive cases of UC were selected for comparison, with extensive renal pelvis involvement and with secondary renal parenchymal invasion. Two cases of collecting duct carcinoma (CDC) were also examined. Immunohistochemistry (IHC) was performed on representative tissue blocks for PAX8, PAX2, CK5, CK7, CK20, p63, GATA3, AMACR, RCC, CD10, vimentin, S100, and MSA. The 10 cases of RCXC (M:F=4:6, ages: 62-91 years, mean: 76) presented with renal masses of 3-6cm. Ureteroscopic studies and renal pelvic washings showed atypical/malignant cells in three cases. Seven patients were treated with nephrectomy followed by radiation±chemotherapy, and all cases developed metastases to lymph nodes or liver/lung/bone. In all 7 cases with nephrectomy, there was extensive renal parenchymal involvement with infiltrating borders and diffuse spread along collecting ducts. Six RCXC-UC contained focal squamous differentiation. The RCXC-SC displayed features of adenoid cystic and basaloid features. In situ UC, with or without papillary components, was identified in the calyces in all 7 nephrectomy cases with remaining renal pelvis harboring small tumor burden in 5 cases, and no tumor in another 2 cases. Of the three cases without nephrectomy, no tumor in the renal pelvis could be visualized with endoscopy, however one case was associated with UC of the urinary bladder. Of 10 control UC cases, tumor was limited to the tip of renal papilla in 7 cases, extensive in 3 cases, and with no extension into the collecting ducts. RCXC-UC were all positive for p63, CK5, CK7, and PAX2, with all negative for RCC. PAX8 (70% positive) and GATA3 (50% positive) reactivity was variable. The 10 UC cases shared IHC properties with RCXC-UC but frequent negativity for PAX8 and positivity for GATA3. RCXC is an aggressive neoplasm with high risk of metastases. Similar to CDC, it is located in the renal papilla and rarely with clinically visible renal pelvis tumor or ureteral urine positive for tumor cells. Unlike CDC and non-calyceal UC, RCXC shows predominantly urothelial and squamous differentiation and is associated with an in situ component of adjacent renal calyces. By IHC, RCXC exhibited features intermediate between UC and CDC with decreased or negative immunoreactivity for PAX8 and GATA.

Value of PAX8, PAX2, napsin A, carbonic anhydrase IX, and claudin-4 immunostaining in distinguishing pleural epithelioid mesothelioma from metastatic renal cell carcinoma

Both mesotheliomas and renal cell carcinomas can present a wide variety of cytomorphologic features and histologic patterns. Because of this, renal cell carcinomas metastatic to the pleura and lung can be confused with mesotheliomas. Recently, a variety of positive carcinoma markers, including kidney-associated markers, have become available. The aim of this study is to investigate the value of some of these markers, specifically PAX8, PAX2, napsin A, carbonic anhydrase IX, and claudin-4, for assisting in distinguishing pleural epithelioid mesotheliomas from metastatic renal cell carcinomas. To do so, a total of 40 pleural epithelioid mesotheliomas and 55 renal cell carcinomas (33 clear cell, 10 papillary, and 12 chromophobe) were investigated. In all, 91% of the renal cell carcinomas expressed claudin-4, 89% PAX8, 60% PAX2, 71% carbonic anhydrase IX, and 29% napsin A. All of the mesotheliomas were positive for carbonic anhydrase IX and were negative for all of the other markers. On the basis of these results, it is concluded that claudin-4 and PAX8 have a higher sensitivity and specificity for assisting in discriminating between pleural epithelioid mesotheliomas and renal cell carcinomas when compared with all of the other positive carcinoma markers that are, at present, recommended to be included in the immunohistochemical panels used in this differential diagnosis. Even though PAX2 and napsin A are highly specific, because of their low sensitivity, they have only a limited value. Carbonic anhydrase IX is not useful.

Value of PAX8, PAX2, claudin-4, and h-caldesmon immunostaining in distinguishing peritoneal epithelioid mesotheliomas from serous carcinomas

Distinguishing between peritoneal epithelioid mesotheliomas and papillary serous carcinomas involving the peritoneum can be difficult on routine histological preparations, but this differential diagnosis can be facilitated by the use of immunohistochemistry. Recent investigations have indicated that PAX8, PAX2, claudin-4, and h-caldesmon are immunohistochemical markers that can assist in distinguishing between these two malignancies; however, much of the information published on the value of these markers is either insufficient or contradictory. The purpose of this study is to resolve some of the existing controversies and to fully determine the practical value of these markers for assisting in the differential diagnosis between peritoneal mesotheliomas and serous carcinomas. In order to do so, a total of 40 peritoneal epithelioid mesotheliomas and 45 serous carcinomas (15 primary, 30 metastatic to the peritoneum) were investigated. PAX8 and PAX2 nuclear positivity was demonstrated in 42 (93%) and 25 (56%) of the serous carcinomas, respectively, whereas none of the mesotheliomas expressed either marker. Forty-four (98%) of the serous carcinomas exhibited claudin-4 reactivity along the cell membrane, whereas none of the mesotheliomas were positive for this marker. All of the serous carcinomas and mesotheliomas were negative for h-caldesmon. Based on these results, it is concluded that PAX8 and claudin-4 have a higher sensitivity and specificity for assisting in discriminating between peritoneal epithelioid mesotheliomas and serous carcinomas when compared with all of the other positive carcinoma markers that are, at present, recommended to be included in the immunohistochemical panels used in this differential diagnosis. Even though it is highly specific, PAX2 has little practical value in the diagnosis of peritoneal epithelioid mesotheliomas as its sensitivity is low. The h-caldesmon is not useful.

PAX2 and PAX8 Expression in Primary and Metastatic Renal Tumors: A Comprehensive Comparison

Context.—The diagnosis of renal cell carcinoma (RCC) remains problematic, especially in the context of metastasis or small-needle biopsies. PAX2 and PAX8 transcription factors are known to be expressed by several histologic types of renal neoplasms.

Objective.—To evaluate the diagnostic utility of PAX2 and PAX8 relative to one another, which has not been studied.

Design.—Consecutive tissue sections from the archival samples of 243 primary and 99 metastatic renal neoplasms were submitted to PAX2 and PAX8 immunostain.

Results.—Within the primary neoplasms, PAX2 versus PAX8 expression was noted in 90 of 95 (95%) versus 92 of 95 (97%) for clear cell RCC, 29 of 38 (76%) versus 38 of 38 (100%) for papillary RCC, 14 of 25 (56%) versus 22 of 25 (88%) for chromophobe RCC, 3 of 7 (43%) versus 5 of 7 (71%) for collecting duct RCC, 6 of 8 (75%) versus 8 of 8 (100%) for acquired cystic kidney disease–related RCC, and 7 of 13 (54%) versus 11 of 13 (85%) for oncocytoma. Regardless of histologic subtype, PAX8 staining was noted in more cells and with more intense staining than PAX2. Within the metastatic RCCs, PAX8 expression was more frequently positive than PAX2 expression (88 of 99 cases; 89%; versus 75 of 99 cases; 76%).

Conclusions.—Both PAX2 and PAX8 are diagnostically useful markers for both primary and metastatic renal neoplasms of a large variety of histologic types. However, PAX8 appears to be more sensitive than PAX2 in both primary and metastatic settings. PAX8 can be included in any immunohistochemical panel for the diagnosis of primary renal neoplasms. Adding PAX2 should be optional, but this would gain limited further diagnostic yield. In a metastatic setting, both PAX8 and PAX2 can be included in a panel because a small subset of metastatic RCCs are stained only with PAX2.

Value of PAX2 immunostaining in tumor diagnosis: a review and update

PAX2 is a member of the PAX family of transcription factors that, together with PAX8, is involved in the regulation of the organogenesis of the kidney and the Müllerian system. Recent investigations have demonstrated that, among tumors, PAX2 is commonly expressed in epithelial tumors of the kidney and female genital tract. Although PAX2 expression has also been reported in B-cell lymphomas and rhabdomyosarcomas, especially alveolar rhabdomyosarcomas, it has been suggested that the positivity in these tumors was most probably due to a cross-reactivity of the anti-PAX2 antibody used in those investigations with other members of the PAX protein family. An analysis of published studies indicates that PAX2 sensitivity for epithelial renal neoplasms and epithelial tumors of the female genital tract is lower than that of PAX8. In contrast to the latter marker, however, PAX2 does not appear to be expressed in epithelial tumors of the thyroid gland or thymus. Because of its restricted expression, PAX2 has proved to be a useful immunohistochemical marker with a wide range of diagnostic applications in surgical pathology, some of which will be briefly reviewed.

Application of immunohistochemistry in the diagnosis of epithelioid mesothelioma: a review and update

A large number of immunohistochemical markers that can assist in the differential diagnosis of epithelioid mesotheliomas are currently available. Because these markers are expressed differently in the various types of carcinomas that can metastasize to the serosal membranes and can potentially be confused with epithelioid mesothelioma, their selection for inclusion in a diagnostic panel largely depends on the differential diagnosis, as well as on which ones work the best in a given laboratory. Traditionally, the panels used in the differential diagnosis of epithelioid mesothelioma have consisted of a combination of positive mesothelioma markers and broad-spectrum carcinoma markers. At present, a wide variety of organ-associated carcinoma markers such as thyroid transcription factor-1 and napsin A for the lung, PAX 8 and PAX 2 for the kidney, and Müllerian-derived tumors; gross cystic disease fluid protein-15 and mammaglobin for the breast; and CDX2 for intestinal differentiation are available, which can assist in establishing the site of origin of an adenocarcinoma when included in a diagnostic panel. This article provides updated information on the composition of the panels of markers recommended in the various differential diagnoses.

Value of PAX 8 immunostaining in tumor diagnosis: a review and update

PAX 8 is a transcription factor involved in the regulation of organogenesis of the thyroid gland, kidney, and Müllerian system. Recent studies have shown that, among tumors, PAX 8 is commonly expressed in epithelial tumors of the thyroid and parathyroid glands, kidney, thymus, and female genital tract. Although PAX 8 expression has also been reported in certain neuroendocrine tumors, including well-differentiated pancreatic neuroendocrine tumors, and duodenal and rectal carcinoids, as well as in B-cell lymphomas, it has recently been shown that the PAX 8 positivity reported in these tumors was due to a cross-reactivity of the antibody used with the N-terminal region of PAX 6 and PAX 5, respectively. Owing to its restricted expression, PAX 8 has proved to be a useful immunohistochemical marker with a wide range of diagnostic applications in surgical pathology, some of which are briefly reviewed.