PAX8 and PAX5 are differentially expressed in B-cell and T-cell lymphomas

Polyclonal PAX8 expression in carcinomas of the biliary tract - Frequent non-specific staining represents a potential diagnostic pitfall

Paired box protein 8 (PAX8) is a transcription factor that is considered a relatively specific marker of carcinomas of the thyroid, kidney, and Müllerian/Wolffian duct derivatives. Unexpected PAX8 immunoreactivity has occasionally been reported in other tumors. The frequency of PAX8 expression in carcinomas of the biliary tract is not well studied. We evaluated the immunohistochemical expression of PAX8 in 73 cases of biliary tract carcinoma. We found that 28 of 73 (38%) biliary tract carcinomas had variable immunoreactivity for PAX8, assessed by a widely used polyclonal antibody (ProteinTech Group, Chicago, IL). This included 3 (4%) of cases with strong diffuse, and 14 (19%) of cases with strong focal staining. Strong PAX8 expression was more frequent in distal bile duct carcinomas than other biliary sites (p = 0.015), and showed a weak association with advanced T stage (T3-T4 versus T1-T2; p = 0.09). No correlation was observed between PAX8 positivity and age at diagnosis, gender, or lymph node metastasis. The 28 polyclonal PAX8-positive cases were largely negative for monoclonal PAX8 and PAX6 immunostains, with only rare tumor cells with weak immunoreactivity being present in a subset of cases. We show that a substantial fraction of biliary tract carcinomas exhibit immunoreactivity with a widely used polyclonal PAX8 antibody. Pathologists should be aware of this potential pitfall during the diagnostic workup of hepatobiliary lesions to avoid misdiagnosis as a metastasis from a PAX8-positive tumor.

2021 American Thyroid Association Guidelines for Management of Patients with Anaplastic Thyroid Cancer

Background: Anaplastic thyroid cancer (ATC) is a rare but highly lethal form of thyroid cancer. Since the guidelines for the management of ATC by the American Thyroid Association were first published in 2012, significant clinical and scientific advances have occurred in the field. The aim of these guidelines is to inform clinicians, patients, and researchers on published evidence relating to the diagnosis and management of ATC. Methods: The specific clinical questions and topics addressed in these guidelines were based on prior versions of the guidelines, stakeholder input, and input of the Task Force members (authors of the guideline). Relevant literature was reviewed, including serial PubMed searches supplemented with additional articles. The American College of Physicians Guideline Grading System was used for critical appraisal of evidence and grading strength of recommendations. Results: The guidelines include the diagnosis, initial evaluation, establishment of treatment goals, approaches to locoregional disease (surgery, radiotherapy, targeted/systemic therapy, supportive care during active therapy), approaches to advanced/metastatic disease, palliative care options, surveillance and long-term monitoring, and ethical issues, including end of life. The guidelines include 31 recommendations and 16 good practice statements. Conclusions: We have developed evidence-based recommendations to inform clinical decision-making in the management of ATC. While all care must be individualized, such recommendations provide, in our opinion, optimal care paradigms for patients with ATC.

The Differential Diagnosis of Medullary-Based Renal Masses

CONTEXT.—

Renal malignancies can be divided into cortical- and medullary-based tumors, the latter of which classically infiltrate the renal parenchyma by extending between nonneoplastic structures. Although high-grade cortical tumors can rarely exhibit the same growth pattern, the infiltrative morphology should elicit a differential diagnosis to be considered in each case. However, these diagnoses can be challenging to distinguish, especially on small renal biopsy samples.

OBJECTIVE.—

To provide an overview of the clinical, gross, and microscopic findings; genetic and molecular alterations; and immunohistochemical evaluation of medullary-based renal tumors and other tumor types with overlapping morphologies and growth patterns.

DATA SOURCES.—

Literature review and personal observations were used to compile the information in this review.

CONCLUSIONS.—

Collecting duct carcinoma is a prototypical medullary-based tumor, and although diagnostic criteria exist, it remains a diagnosis of exclusion, especially with ancillary techniques aiding the recognition of established as well as more recently described neoplasms. Other medullary-based malignancies included in the differential diagnosis include renal medullary carcinoma/renal cell carcinoma unclassified with medullary phenotype, fumarate hydratase-deficient renal cell carcinoma, and upper tract urothelial carcinoma. Moreover, other rare entities should be excluded, including metastatic carcinoma, lymphoma, and melanoma. In addition to potential prognostic differences, accurate diagnoses can have important surgical and clinical management implications.

Analysis of PAX8 immunohistochemistry in lung cancers: a meta-analysis

BACKGROUND

In this meta-analysis, we aimed to evaluate the PAX8 immunohistochemical expressions in primary lung cancers and metastatic cancers to the lung.

METHODS

We identified and reviewed relevant articles from the PubMed databases. Ultimately, 18 articles were included in this meta-analysis. PAX8 expression rates were analyzed and compared between primary and metastatic lung cancers.

RESULTS

The PAX8 expression rate in primary lung cancers was 0.042 (95% confidence interval [CI], 0.025 to 0.071). PAX8 expression rates of small cell (0.129; 95% CI, 0.022 to 0.496) and non-small cell carcinomas of the lung (0.037; 95% CI, 0.022 to 0.061) were significantly different (p=.049 in a meta-regression test). However, the PAX8 expression rates of adenocarcinoma (0.013; 95% CI, 0.006 to 0.031) and squamous cell carcinoma (0.040; 95% CI, 0.016 to 0.097) were not significantly different. PAX8 expression rates of metastatic carcinomas to the lung varied, ranging from 1.8% to 94.9%. Metastatic carcinomas from the lung to other organs had a PAX8 expression rate of 6.3%. The PAX8 expression rates of metastatic carcinomas from the female genital organs, kidneys, and thyroid gland to the lung were higher than those of other metastatic carcinomas.

CONCLUSIONS

Primary lung cancers had a low PAX8 expression rate regardless of tumor subtype. However, the PAX8 expression rates of metastatic carcinomas from the female genital organs, kidneys, and thyroid were significantly higher than those of primary lung cancers.

A Comprehensive Review of Biomarker Use in the Gynecologic Tract Including Differential Diagnoses and Diagnostic Pitfalls

Morphologic (ie, hematoxylin and eosin) evaluation of the Mullerian tract remains the gold standard for diagnostic evaluation; nevertheless, ancillary/biomarker studies are increasingly utilized in daily practice to assist in the subclassification of gynecologic lesions and tumors. The most frequently utilized "biomarker" technique is immunohistochemistry; however, in situ hybridization (chromogenic and fluorescence), chromosomal evaluation, and molecular analysis can also be utilized to aid in diagnosis. This review focuses on the use of immunohistochemistry in the Mullerian tract, and discusses common antibody panels, sensitivity and specificity of specific antibodies, and points out potential diagnostic pitfalls when using such antibodies.

Practical Application of Lineage-Specific Immunohistochemistry Markers: Transcription Factors (Sometimes) Behaving Badly

CONTEXT.—

Transcription factors (TFs) are proteins that regulate gene expression and control RNA transcription from DNA. Lineage-specific TFs have increasingly been used by pathologists to determine tumor lineage, especially in the setting of metastatic tumors of unknown primary, among other uses. With experience gathered from its daily application and increasing pitfalls reported from immunohistochemical studies, these often-touted highly specific TFs are not as reliable as once thought.

OBJECTIVES.—

To summarize the established roles of many of the commonly used TFs in clinical practice and to discuss known and potential sources for error (eg, false-positivity from cross-reactivity, aberrant, and overlap "lineage-specific" expression) in their application and interpretation.

DATA SOURCES.—

Literature review and the authors' personal practice experience were used. Several examples selected from the University Health Network (Toronto, Ontario, Canada) are illustrated.

CONCLUSIONS.—

The application of TF diagnostic immunohistochemistry has enabled pathologists to better assess the lineage/origin of primary and metastatic tumors. However, the awareness of potential pitfalls is essential to avoid misdiagnosis.

Renal medullary carcinoma in a young mixed-race man in Japan

Renal medullary carcinoma (RMC) is a rare and aggressive cancer associated with the sickle cell trait. The diagnosis of RMC depends on recognition of its histologic features and immunohistochemical deficiency of INI1, but correct diagnosis is sometimes difficult, especially if a patient's information on race, past, and family medical history is unclear. At present, this is the first report on RMC in Japan.

Morphological characterization of canine retrobulbar lymphoma

This report characterized seven cases of canine retrobulbar lymphoma that have been diagnosed during 2008 to 2014 by immunophenotyping of CD3 and Pax5. Classification of lymphoma were performed according to the revised WHO guidelines. Four retrobulbar lymphomas were of T-cell origin, while the others were of B-cell. Out of 7 cases, four subtypes were diagnosed in this study; T-cell-rich large B-cell lymphoma (3/7), T-cell lymphoblastic lymphoma (2/7), peripheral T-cell lymphoma (1/7), and cutaneous nonepitheliotropic lymphoma (1/7). T-cell-rich large B-cell lymphoma was found to be the most frequent subtype found.

PAX8-Positive B-Cell Lymphoma in Adrenal Gland Masquerading as Metastatic Renal Cell Carcinoma

Extranodal lymphomas involve adrenal glands as a mass lesion in 3% to 5% of cases as identified by imaging studies. Definitive diagnosis of the neoplasm is provided by morphological and immunophenotypical evaluation on limited tissue obtained by fine needle aspiration or core biopsy. We report a diagnostically challenging case that presented as masses involving adrenal gland and lung in the setting of a concurrent primary renal cell carcinoma. PAX8, a frequently used marker for renal cell carcinoma, was immunoreactive in the neoplastic cells of the adrenal mass, and thus highly suggestive for metastatic renal cell carcinoma. The neoplasm was eventually proven to represent PAX8-positive diffuse large B-cell lymphoma after extended immunohistochemical workup. This case of unusual presentation of synchronous renal cell carcinoma and adrenal lymphoma with overlapping PAX8 immunoreactivity serves as a potential diagnostic pitfall with significant clinical implications.

PAX8 Distinguishes Diffuse Large B-Cell Lymphoma Mimicking Sarcoma

PAX8 is important for embryogenesis of the thyroid, Müllerian system, and upper urinary/renal tract, and expression of PAX8 has been described in carcinomas from each of these sites. The sensitivity and specificity of the polyclonal PAX8 antibody in a large cohort of epithelial tumors as well as lymphomas have been previously determined, the latter because polyclonal PAX8 is known to be immunoreactive in nonneoplastic B-cell lymphocytes which are often used as the positive internal control for immunohistochemistry. In this case report, PAX8 was a diagnostic clue for revising a previous diagnosis of unclassified high grade sarcoma to diffuse large B-cell lymphoma. This case report demonstrates a pitfall for PAX8 immunoreactivity and acts as a reminder that lymphoma should be included in the differential diagnosis of a PAX8 positive, epithelial cell marker negative tumor of unknown primary origin.

Inhibition of Pax2 Transcription Activation with a Small Molecule that Targets the DNA Binding Domain

The Pax gene family encodes DNA binding transcription factors that control critical steps in embryonic development and differentiation of specific cell lineages. Often, Pax proteins are re-expressed or ectopically expressed in cancer and other diseases of abnormal proliferation, making them attractive targets for tissue specific inhibition by small molecules. In this report, we used a homology model of the Pax2 paired domain and a virtual screen to identify small molecules that can inhibit binding of the paired domain to DNA and Pax2 mediated transcription activation. Candidates from the virtual screen were then confirmed in a cell based Pax2 transactivation assay. Subsequently, we tested analogs of these hits to identify a single compound that effectively blocked Pax2 activity and DNA binding with a K_d of 1.35-1.5 μM. The compound, termed EG1, was used to inhibit embryonic kidney development, a process directly dependent on Pax2 activity. Furthermore, we show that EG1 can inhibit proliferation of Pax2 positive renal and ovarian cancer cell lines but has little effect on Pax2 negative cancer cells. These data confirm that small molecules targeting the DNA binding paired domain can be identified and may be good lead compounds for developing tissue and cell-type specific anticancer therapies.

Undifferentiated Malignant Neoplasm Involving Parotid and Thyroid: Sampling and PAX8 Cross-Reactivity Can Obscure the Diagnosis of Lymphoma

Poorly differentiated malignant neoplasia arising within the head and neck region may originate from diverse sources. We report a case of a cytologically undifferentiated malignant neoplasm clinically presenting as masses involving thyroid and parotid. Although PAX8 was immunoreactive and thus worrisome for anaplastic thyroid carcinoma, the tumor was eventually proven to represent PAX5 positive diffuse large B-cell lymphoma expressing cross-reactivity with polyclonal PAX8 antibody. Cross-reactivity between commercially available polyclonal PAX8 and PAX5 immunostains has been described in the literature but is not widely known, and it is a potential pitfall for making a misdiagnosis. This distinction can have importance in selection of subsequent clinical therapy and should be considered in choice of immunohistochemical stains for diagnostic purposes.

Evaluation of PAX8 Expression and Its Potential Diagnostic and Prognostic Value in Renal and Extra-Renal Ewing Sarcomas/PNETs

PAX8 is a transcription factor involved in the regulation of organogenesis of the thyroid gland, kidney, and Müllerian system. It is commonly expressed in epithelial tumors of thyroid and parathyroid glands, kidney, thymus, and female genital tract. PAX8 is increasingly used in the establishment of tissue of origin in carcinomas and has recently been identified in a subset of small blue round cell tumors including Ewing sarcomas/PNETs. However, it is unclear if this association in ES/PNETs is due to renal origin or is PNET specific. In this study we investigated the PAX8 staining pattern of primary renal and extra-renal ES/PNETs to explore its potential diagnostic and prognostic role. A tissue microarray (TMA) of 22 cases of extra-renal Ewing/PNETs and two separate cases of primary renal PNET whole slide sections were immunohistochemically stained with rabbit polyclonal PAX8 antibody. PAX8 was positive in 2 of 2 primary renal PNETs and in 14 (64 %) cases of the extra renal PNETs. The association between PAX8 immunoreactivity and Ewing/PNET was identified in both primary renal and extra-renal Ewing/PNETs for the first time. Further studies are warranted to verify these findings and to shed light in the tumorigenesis of Ewing/PNET. However, PAX8 is not useful in establishing a diagnosis of Ewing/PNET due to its presence in different tumors like carcinomas, lymphomas and sarcomas. PAX8 does not seem to have prognostic value.