False-negative Papanicolaou tests in women with biopsy-proven invasive endocervical adenocarcinoma/adenocarcinoma in situ: a retrospective analysis with assessment of interobserver agreement.

INTRODUCTION: The objectives of our study were to identify factors contributing to false-negative Papanicolaou (Pap) tests in patients with endocervical adenocarcinoma (EA) or adenocarcinoma in situ (AIS), and to analyze the impact of educational instruction on interobserver agreement in these cases. MATERIALS AND METHODS: False-negative Pap tests from patients with EA/AIS were reviewed by a consensus group and by 12 individual reviewers in 2 rounds, with an educational session on glandular neoplasia in Pap tests conducted between the 2 rounds. RESULTS: Of 79 Pap tests from patients with EA/AIS, 57 (72.2%) were diagnosed as abnormal and 22 (27.8%) as negative. Of the 22 false-negative cases, 10 remained negative on consensus review, with false-negative diagnoses attributed to sampling variance. The other 12 cases were upgraded to epithelial abnormalities (including 8 to glandular lesions). The false-negative diagnoses were attributed to screening variance in 2 cases and interpretive variance in 10 cases. On individual review, abnormal cells were misinterpreted as reactive glandular cells or endometrial cells in 7 of 8 and 5 of 8 cases upgraded to glandular abnormalities, respectively. With education, the proportion of individual reviewers demonstrating at least moderate agreement with the consensus diagnosis (Cohen's kappa >0.4) increased from 33% (4 of 12) to 75% (9 of 12). CONCLUSIONS: Sampling and interpretive variance each accounted for nearly one-half of the false-negative Pap tests, with underclassification as reactive glandular or endometrial cells the main source of the interpretive variances. Educational instruction significantly decreased the interpretive variance and interobserver variability in the diagnosis of glandular abnormalities.

Targeting progesterone signaling prevents metastatic ovarian cancer.

Effective cancer prevention requires the discovery and intervention of a factor critical to cancer development. Here we show that ovarian progesterone is a crucial endogenous factor inducing the development of primary tumors progressing to metastatic ovarian cancer in a mouse model of high-grade serous carcinoma (HGSC), the most common and deadliest ovarian cancer type. Blocking progesterone signaling by the pharmacologic inhibitor mifepristone or by genetic deletion of the progesterone receptor (PR) effectively suppressed HGSC development and its peritoneal metastases. Strikingly, mifepristone treatment profoundly improved mouse survival (∼18 human years). Hence, targeting progesterone/PR signaling could offer an effective chemopreventive strategy, particularly in high-risk populations of women carrying a deleterious mutation in the BRCA gene.

In vivo modeling of metastatic human high-grade serous ovarian cancer in mice.

Metastasis is responsible for 90% of human cancer mortality, yet it remains a challenge to model human cancer metastasis in vivo. Here we describe mouse models of high-grade serous ovarian cancer, also known as high-grade serous carcinoma (HGSC), the most common and deadliest human ovarian cancer type. Mice genetically engineered to harbor Dicer1 and Pten inactivation and mutant p53 robustly replicate the peritoneal metastases of human HGSC with complete penetrance. Arising from the fallopian tube, tumors spread to the ovary and metastasize throughout the pelvic and peritoneal cavities, invariably inducing hemorrhagic ascites. Widespread and abundant peritoneal metastases ultimately cause mouse deaths (100%). Besides the phenotypic and histopathological similarities, mouse HGSCs also display marked chromosomal instability, impaired DNA repair, and chemosensitivity. Faithfully recapitulating the clinical metastases as well as molecular and genomic features of human HGSC, this murine model will be valuable for elucidating the mechanisms underlying the development and progression of metastatic ovarian cancer and also for evaluating potential therapies.

Successful yolk-sac tumor treatment with fertility-sparing partial oophorectomy.

Yolk-sac tumors account for about 20% of ovarian germ cell tumors and occur predominantly in women below 35 years of age. Modern evidence-based treatment strategies have ensured long term post-treatment survival, but with increased survival, attention has been turned to an urgent need for developing fertility sparing treatment strategies. In this report we describe the successful treatment of a young woman who was able to conceive and deliver two children, in spite of the loss of one ovary two years prior to being diagnosed with an ovarian yolk-sac tumor on the remaining ovary.

Cell Origins of High-Grade Serous Ovarian Cancer.

High-grade serous ovarian cancer, also known as high-grade serous carcinoma (HGSC), is the most common and deadliest type of ovarian cancer. HGSC appears to arise from the ovary, fallopian tube, or peritoneum. As most HGSC cases present with widespread peritoneal metastases, it is often not clear where HGSC truly originates. Traditionally, the ovarian surface epithelium (OSE) was long believed to be the origin of HGSC. Since the late 1990s, the fallopian tube epithelium has emerged as a potential primary origin of HGSC. Particularly, serous tubal intraepithelial carcinoma (STIC), a noninvasive tumor lesion formed preferentially in the distal fallopian tube epithelium, was proposed as a precursor for HGSC. It was hypothesized that STIC lesions would progress, over time, to malignant and metastatic HGSC, arising from the fallopian tube or after implanting on the ovary or peritoneum. Many clinical studies and several mouse models support the fallopian tube STIC origin of HGSC. Current evidence indicates that STIC may serve as a precursor for HGSC in high-risk women carrying germline BRCA1 or 2 mutations. Yet not all STIC lesions appear to progress to clinical HGSCs, nor would all HGSCs arise from STIC lesions, even in high-risk women. Moreover, the clinical importance of STIC remains less clear in women in the general population, in which 85⁻90% of all HGSCs arise. Recently, increasing attention has been brought to the possibility that many potential precursor or premalignant lesions, though composed of microscopically-and genetically-cancerous cells, do not advance to malignant tumors or lethal malignancies. Hence, rigorous causal evidence would be crucial to establish that STIC is a bona fide premalignant lesion for metastatic HGSC. While not all STICs may transform into malignant tumors, these lesions are clearly associated with increased risk for HGSC. Identification of the molecular characteristics of STICs that predict their malignant potential and clinical behavior would bolster the clinical importance of STIC. Also, as STIC lesions alone cannot account for all HGSCs, other potential cellular origins of HGSC need to be investigated. The fallopian tube stroma in mice, for instance, has been shown to be capable of giving rise to metastatic HGSC, which faithfully recapitulates the clinical behavior and molecular aspect of human HGSC. Elucidating the precise cell(s) of origin of HGSC will be critical for improving the early detection and prevention of ovarian cancer, ultimately reducing ovarian cancer mortality.

Negative Pap tests in women with high-grade cervical lesions on follow-up biopsies: Contributing factors and role of human papillomavirus genotyping.

BACKGROUND: Previous studies have indicated that negative Papanicolaou (Pap) tests can precede high-grade cervical lesions (HGCL) on biopsy. This study aims to determine the contributing factors for cytologic discrepancy and the potential role of human papilloma virus (HPV) testing in risk evaluation of women with negative Pap tests. METHODS: Of 42,797 Pap tests interpreted as negative for intraepithelial lesion or malignancy (NILM) from March 1, 2013 to December 30, 2014, 426 had available HPV testing and follow-up biopsy. The NILM Pap tests with biopsy-confirmed HGCL were reviewed. RESULTS: Among 426 cytology-negative cases, the biopsies showed benign histology in 243 (57%), low-grade squamous intraepithelial lesion in 157 (37%), HGCL in 22 (5%), and endometrial adenocarcinoma in 4 (1%) cases. The sensitivity/specificity/positive predictive values (PPV) of high-risk HPV (hrHPV) and HPV16/18 tests in predicting HGCL was 91%/45%/8% and 55%/76%/11%, respectively. Upon review of NILM Pap tests with biopsy-confirmed HGCL, the contributing factors to negative cytology included absence of abnormal cells (12/21, 57%) or diagnostic high-grade cells (6/21, 29%), unsatisfactory samples (2/21, 10%), and interpretation variances (1/21, 5%). Interpretation variances in three high-risk lesions (1 HSIL, 2 ASC-H) were influenced by marked obscuring inflammation. CONCLUSIONS: Our study demonstrated that 5% of women underwent co-testing with negative Pap tests had HGCL on follow-up biopsy. Absence of diagnostic cells was the leading cause for cytology discrepancy and interpretation variances were influenced by marked obscuring inflammation. HPV testing and genotyping had limited value in risk stratification due to extremely low PPV. Focused rescreening of hrHPV-positive NILM with obscuring factors may help reduce interpretation variances.

The ovary is an alternative site of origin for high-grade serous ovarian cancer in mice.

Although named "ovarian cancer," it has been unclear whether the cancer actually arises from the ovary, especially for high-grade serous carcinoma (HGSC), also known as high-grade serous ovarian cancer, the most common and deadliest ovarian cancer. In addition, the tumor suppressor p53 is the most frequently mutated gene in HGSC. However, whether mutated p53 can cause HGSC remains unknown. In this study, we bred a p53 mutation, p53(R172H), into conditional Dicer-Pten double-knockout (DKO) mice, a mouse model duplicating human HGSC, to generate triple-mutant (TKO) mice. Like DKO mice, these TKO mice develop metastatic HGSCs originating from the fallopian tube. Unlike DKO mice, however, even after fallopian tubes are removed in TKO mice, ovaries alone can develop metastatic HGSCs, indicating that a p53 mutation can drive HGSC arising from the ovary. To confirm this, we generated p53(R172H)-Pten double-mutant mice, one of the genetic control lines for TKO mice. As anticipated, these double-mutant mice also develop metastatic HGSCs from the ovary, verifying the HGSC-forming ability of ovaries with a p53 mutation. Our study therefore shows that ovaries harboring a p53 mutation, as well as fallopian tubes, can be a distinct tissue source of high-grade serous ovarian cancer in mice.

The Utility of Core Needle Biopsy and Fine-Needle Aspiration in the Workup of Tumors of Suspected Müllerian Origin.

OBJECTIVES: Core needle biopsy (CNB) and fine-needle aspiration (FNA) for tumors of suspected Müllerian origin may prevent unnecessary laparotomies and allow patients the benefit of neoadjuvant chemotherapy. An assessment of the utility and limitations of CNB/FNA, with incorporation of current immunohistochemistry, is needed. STUDY DESIGN: Two hundred nineteen female patients with CNB/FNA of the omentum, pelvis, abdomen, adnexa, ovary, uterus, and fallopian tube were identified. From these, 30 consecutive CNB/FNA with corresponding surgical resection were reviewed to assess diagnostic agreement and identify potential diagnostic pitfalls. RESULTS: The most frequent diagnosis overall was adenocarcinoma (96/219; 43.8%), most commonly adenocarcinoma of gynecologic origin (65/219; 30%). Nondiagnostic or unsatisfactory material was present in a minority of cases (10/219; 5%). In the 30 CNB/FNA cases examined for diagnostic agreement with surgical resection, 24 (80%) had exact or essential agreement with the final diagnosis. Of the 23 cases that were positive and/or suspicious on cytology, 18 (78%) had neoadjuvant chemotherapy or radiation treatment prior to surgical resection. CONCLUSIONS: The majority of CNB/FNA for tumors of suspected Müllerian origin are diagnostic, correlate with the surgical resection, and contribute to management. A standard diagnostic algorithm is suggested.

PAX2 and PAX8: useful markers for metastatic effusions.

OBJECTIVE: It was the aim of this study to determine the utility of PAX2 and PAX8 in cytology effusions with metastatic tumor. STUDY DESIGN: PAX2 and PAX8 immunohistochemical staining was performed on cell blocks of 89 pleural, pericardial and peritoneal effusions with benign diagnoses (18 cases), or secondary to renal cell carcinoma (RCC; 9 cases), müllerian carcinoma (21 cases) or non-müllerian carcinoma (41 cases). RESULTS: PAX2 stained 0% (0/18) of controls, 100% (8/8) of RCCs, 35% (7/20) of müllerian carcinomas, and 2% (1/41) of non-müllerian carcinomas. PAX8 stained 6% (1/18) of control cases, 100% (9/9) of RCC cases, 100% (20/20) of müllerian carcinomas, and 5% (2/41) of non-müllerian carcinomas. PAX2 was 35% sensitive and 95% specific for müllerian carcinoma and 100% sensitive and 95% specific for RCC. PAX8 was 100% sensitive and 95% specific for müllerian carcinoma and 100% sensitive and 95% specific for RCC. CONCLUSIONS: PAX8 is more sensitive than PAX2 for metastatic effusions from müllerian carcinomas (100 vs. 35%), while also having a higher intensity of staining than PAX2. However, PAX2 and PAX8 are both highly sensitive and specific for RCCs. PAX2 and PAX8 are valuable diagnostic markers for metastatic müllerian carcinomas and RCCs in effusion cytology. PAX8 is superior for carcinomas of müllerian origin.

Genotype-specific prevalence and distribution of human papillomavirus genotypes in underserved Latino women with abnormal Papanicolaou tests.

INTRODUCTION: Knowledge about the prevalence and distribution of human papillomavirus (HPV) genotypes in cervical premalignant and malignant lesions is crucial to guide development of clinical management strategies and prophylactic vaccines. The aim of this study was to determine HPV genotype-specific prevalence and distribution in an underserved cohort of Latino women. MATERIALS AND METHODS: From December 2009 to April 2011, 808 SurePath cervicovaginal specimens were collected from women who were referred from charity clinics for abnormal Papanicolaou tests. The patients' average age was 36.5 years (range 19-85 years). The specimens were tested for HPV genotypes by DNA microarray and sequencing assays. RESULTS: The HPV infection rate was extremely high (93% for any HPV and 64% for high-risk [HR]-HPV), with frequent multiple-strain infection (39%). Younger age (<30 years) was associated with frequent HR-HPV infection, multiple strain infections, and cytologic abnormalities. When compared with previous reports, HPV 16 remained the most common genotype (44.6%) in women with high-grade squamous intraepithelial lesion; however, a significant increase in HPV 31 (17.9%) and 45 (10.7%) and a decrease in HPV 35, 52, 33, and 66 were observed. CONCLUSIONS: The HPV genotype-specific prevalence and distribution pattern in this cohort of underserved Latino women differed significantly from previously published data in the United States. Understanding the potentially changing trends in HPV distribution pattern will help guide the development of appropriate preventive and therapeutic strategies for both underserved and general populations.

Tumor-to-tumor metastasis with endometrial carcinoma metastatic to squamous cell carcinoma of vulva: the first reported case.

Endometrial carcinoma metastasizing to the vulva is a rare occurrence, with only 15 reported cases in the literature. To our knowledge, no cases of tumor-to-tumor metastasis involving endometrial carcinoma as a donor tumor have ever been published. We report the first case of an endometrial carcinoma as a donor tumor metastasizing to a squamous cell carcinoma of the vulva, a recipient tumor. A 79-year-old woman with a history of endometrioid adenocarcinoma of the uterus presented with a vulvar lesion. Pathologic examination of the excised lesion confirmed the presence of metastatic endometrioid adenocarcinoma; however, it was found within a well-differentiated squamous cell carcinoma of the vulva. Surrounding the squamous cell carcinoma was a background of a high-grade vulvar intraepithelial lesion (vulvar intraepithelial neoplasia 3), and immunohistochemistry confirmed the presence of 2 separate tumors involved in a tumor-to-tumor metastasis. This unique case highlights the importance of awareness of the phenomenon, and expands the current spectrum of tumor-to-tumor metastases.

Expression and functional pathway analysis of nuclear receptor NR2F2 in ovarian cancer.

CONTEXT: Recent evidence implicates the orphan nuclear receptor, nuclear receptor subfamily 2, group F, member 2 (NR2F2; chicken ovalbumin upstream promoter-transcription factor II) as both a master regulator of angiogenesis and an oncogene in prostate and other human cancers. OBJECTIVE: The objective of the study was to determine whether NR2F2 plays a role in ovarian cancer and dissect its potential mechanisms of action. DESIGN, SETTING, AND PATIENTS: We examined NR2F2 expression in healthy ovary and ovarian cancers using quantitative PCR and immunohistochemistry. NR2F2 expression was targeted in established ovarian cancer cell lines to assess the impact of dysregulated NR2F2 expression in the epithelial compartment of ovarian cancers. RESULTS: Our results indicate that NR2F2 is robustly expressed in the stroma of healthy ovary with little or no expression in epithelia lining the ovarian surface, clefts, or crypts. This pattern of NR2F2 expression was markedly disrupted in ovarian cancers, in which decreased levels of stromal expression and ectopic epithelial expression were frequently observed. Ovarian cancers with the most disrupted patterns of NR2F2 were associated with significantly shorter disease-free interval by Kaplan-Meier analysis. Targeting NR2F2 expression in established ovarian cancer cell lines enhanced apoptosis and increased proliferation. In addition, we found that NR2F2 regulates the expression of NEK2, RAI14, and multiple other genes involved in the cell cycle, suggesting potential pathways by which dysregulated expression of NR2F2 impacts ovarian cancer. CONCLUSIONS: These results uncover novel roles for NR2F2 in ovarian cancer and point to a unique scenario in which a single nuclear receptor plays potentially distinct roles in the stromal and epithelial compartments of the same tissue.

Digital slide imaging in cervicovaginal cytology: a pilot study.

CONTEXT: Digital whole slide imaging is the anticipated future of anatomic pathology, where sign-out of glass slides will be replaced by scanned images. Whole slide imaging has been successfully used in surgical pathology, but its usefulness and clinical application have been limited in cytology for several reasons, including lack of availability of z-axis depth focusing and large file size. Recently, several systems have become available in the United States for whole slide imaging with z-axis technology. OBJECTIVE: To determine the accuracy and efficiency of whole slide imaging, as compared with traditional glass slides, for use in cervicovaginal diagnostic cytology. DESIGN: Eleven cervicovaginal cytology cases (ThinPrep and SurePath) scanned at ×20, ×40, and ×40 z-stack magnifications using the BioImagene iScan Coreo Au 3.0 scanner were evaluated by 4 cytotechnologists and 3 pathologists in a blinded study. Different magnification scans were recorded as separate cases and presented in a randomized sequence. Corresponding glass slides were also reviewed. For each case, the diagnoses and total time to reach each diagnosis were recorded. RESULTS: Diagnostic accuracy was higher and average time per case was lower with glass slides as compared with all digital images. Among the digital images, the ×40 or ×40 z-stack had the highest diagnostic accuracy and lowest interpretation time. CONCLUSIONS: Whole slide imaging is a viable option for the purposes of teaching and consultations, and as a means of archiving cases. However, considering the large file size and total time to reach diagnosis on digital images, whole slide imaging is not yet ready for daily cervicovaginal diagnostic cytology screening use.

Should LSIL-H be a distinct cytology category?: A study on the frequency and distribution of 40 human papillomavirus genotypes in 808 women.

BACKGROUND: The 2001 Bethesda System for gynecologic cervical cytology reporting classifies squamous intraepithelial lesions into low-grade (LSIL) and high-grade (HSIL) lesions. An intermediate term, "low-grade squamous intraepithelial lesion, cannot exclude high-grade squamous intraepithelial lesion (LSIL-H)," has been used in a small percentage of LSIL cases. To the authors' knowledge, little is known regarding the human papillomavirus (HPV) status in patients with LSIL-H. METHODS: A total of 808 SurePath specimens obtained between December 2009 and April 2011 were tested for 40 HPV genotypes using DNA microarray, followed by a confirmatory DNA sequencing assay. RESULTS: The infection rate for high-risk HPV in women with LSIL-H (92%) was strikingly close to that for women with HSIL (91%), which was higher than that for those with LSIL (74%); atypical squamous cells, cannot rule out high-grade lesion (ASC-H) (78%); or LSIL and ASC-H combined (74%). HPV type 16, the most common carcinogenic HPV genotype, was detected in 36% of women with LSIL-H, which was significantly higher than that in women with LSIL and ASC-H combined (13.8%), but less than that in women with HSIL (44.6%). Patients with LSIL-H and HSIL had similar infection rates for low-risk/intermediate-risk HPV genotypes, which were lower than those in LSIL or LSIL and ASC-H combined. CONCLUSIONS: Women found to have LSIL-H on a Papanicolaou test appear to have a unique HPV distribution pattern that clearly differs from LSIL and is comparable to that for HSIL, suggesting an increased risk of high-grade lesions over that of women with LSIL. Recognizing LSIL-H as an independent diagnostic category may help in the early identification of the high-risk subgroup that may require a management algorithm comparable to that for patients with HSIL. Cancer (Cancer Cytopathol) 2012. © 2012 American Cancer Society.

High-grade serous ovarian cancer arises from fallopian tube in a mouse model.

Although ovarian cancer is the most lethal gynecologic malignancy in women, little is known about how the cancer initiates and metastasizes. In the last decade, new evidence has challenged the dogma that the ovary is the main source of this cancer. The fallopian tube has been proposed instead as the primary origin of high-grade serous ovarian cancer, the subtype causing 70% of ovarian cancer deaths. By conditionally deleting Dicer, an essential gene for microRNA synthesis, and Pten, a key negative regulator of the PI3K pathway, we show that high-grade serous carcinomas arise from the fallopian tube in mice. In these Dicer-Pten double-knockout mice, primary fallopian tube tumors spread to engulf the ovary and then aggressively metastasize throughout the abdominal cavity, causing ascites and killing 100% of the mice by 13 mo. Besides the clinical resemblance to human serous cancers, these fallopian tube cancers highly express genes that are known to be up-regulated in human serous ovarian cancers, also demonstrating molecular similarities. Although ovariectomized mice continue to develop high-grade serous cancers, removal of the fallopian tube at an early age prevents cancer formation--confirming the fallopian tube origin of the cancer. Intriguingly, the primary carcinomas are first observed in the stroma of the fallopian tube, suggesting that these epithelial cancers have a mesenchymal origin. Thus, this mouse model demonstrates a paradigm for the origin and initiation of high-grade serous ovarian carcinomas, the most common and deadliest ovarian cancer.

Identification of tissue of origin in body fluid specimens using a gene expression microarray assay.

BACKGROUND: Body fluid specimens may be the first and only pathologic specimen for clinical evaluation in metastatic cancer cases. The challenge of identifying the tissue of origin in metastatic cancer has led to the emergence of molecular-based assays, such as the microarray-based Pathwork Tissue of Origin gene expression test. The ability to use body fluid specimens in this test would be valuable in providing diagnoses to cancer patients without clearly identifiable primary sites. In the current study, the authors evaluated the Tissue of Origin Test for use with malignant effusion specimens. METHODS: A total of 27 metastasis-positive body fluid specimens from different body sites, including pleural, ascites, pericardial, and pelvic wash fluids, were obtained from patients with known diagnoses. Nine specimens from nonmalignant body fluids were included as controls. RNA was extracted from formalin-fixed, paraffin-embedded (FFPE) tissue and gene expression analysis was performed with the Tissue of Origin Test. RESULTS: Seventeen of 27 metastasis-positive samples were non-necrotic with ≥60% tumor and yielded sufficient RNA. Of these samples, 94.1% (16 of 17) were in agreement with the available diagnosis. Of the 9 negative control samples evaluated, 7 (77.8%) demonstrated microarray expression profiles most similar to lymphoma, which is consistent with the predominance of inflammatory cells in these specimens. CONCLUSIONS: The results of the current study demonstrated that FFPE cell blocks from cytologic body fluid specimens yield adequate diagnostic material for the Pathwork test and can be used in the workup of patients with unknown primary tumors.

PAX2 and PAX8 expression in primary and metastatic müllerian epithelial tumors: a comprehensive comparison.

PAX2 and PAX8 are transcription factors that are essential in embryonic development of müllerian organs. They may also play a role in tumor development in these organs. The diagnostic utility of PAX2 and PAX8 relative to one another has not been comprehensively studied. Archival tissue samples for normal or non-neoplastic tissue (251), primary epithelial neoplasms (316 for PAX2 and 357 for PAX8), and metastatic epithelial neoplasms (16), all of müllerian origin, were subjected to PAX2 and PAX8 immunostaining. The staining frequency, extent, and intensity for these markers were compared. Virtually identical PAX2 and PAX8 expressions were noted in non-neoplastic tissue. They were constantly seen in most epithelial cells (but not in stromal cells) of the endocervix, endometrium, fallopian tube, paratubal cyst, endosalpingiosis, endometriosis, and endometrial polyp. Within the primary epithelial neoplasms, PAX2 and PAX8 expression was noted in 55% and 98% of serous tumors, 25% and 94% of endometrioid tumors, 19% and 100% of clear cell tumors, 11% and 67% of transitional/undifferentiated tumors, and 10% and 22% of mucinous tumors, respectively. Regardless of histologic subtypes, PAX2 staining was noted in fewer cells and with less staining intensity compared with PAX8. No tumor showed only PAX2 staining. Within the metastatic carcinomas, PAX2 and PAX8 expression was noted in 38% and 98% of cases, respectively, with a diffuse and strong staining for PAX8, contrasting with a patchy and weak PAX2 expression. PAX2 and PAX8 are constantly expressed in normal or non-neoplastic tissue of müllerian origin. For primary and metastatic müllerian epithelial tumors, PAX8 shows strong and diffuse staining in most cases of all histologic subtypes, except in mucinous tumors. In contrast, PAX2 expression is always less than PAX8, and exclusive staining for PAX2 is not seen. PAX8 supersedes PAX2 as probably the best epithelial marker hitherto for primary or metastatic müllerian epithelial tumors.