Utility of Immunohistochemistry in the Diagnosis of Pleuropulmonary and Mediastinal Cancers: A Review and Update

CONTEXT.—

Immunohistochemistry has become a valuable ancillary tool for the accurate classification of pleuropulmonary and mediastinal neoplasms necessary for therapeutic decisions and predicting prognostic outcome. Diagnostic accuracy has significantly improved because of the continuous discoveries of tumor-associated biomarkers and the development of effective immunohistochemical panels.

OBJECTIVE.—

To increase the accuracy of diagnosis and classify pleuropulmonary neoplasms through immunohistochemistry.

DATA SOURCES.—

Literature review and the author's research data and personal practice experience.

CONCLUSIONS.—

This review article highlights that appropriately selecting immunohistochemical panels enables pathologists to effectively diagnose most primary pleuropulmonary neoplasms and differentiate primary lung tumors from a variety of metastatic tumors to the lung. Knowing the utilities and pitfalls of each tumor-associated biomarker is essential to avoid potential diagnostic errors.

PAX1 expression in thymic epithelial neoplasms and morphologic mimics

Thymic epithelial neoplasms are morphologically diverse and can pose a diagnostic challenge that is complicated by a lack of immunohistochemistry (IHC) markers that are entirely sensitive and specific for thymic epithelium. Polyclonal PAX8 is often used in this context, but it is not a specific marker. The PAX1 transcription factor shares significant homology with PAX8 and plays an integral role in thymic development in humans and murine models. This study evaluated the role of PAX1 IHC in differentiating thymic epithelial neoplasms from morphologic mimics on whole slide tissue sections. The PAX1 antibody stained all 74 thymoma cases; however, there was wide variability in staining intensity within each subtype. The antibody was less sensitive in thymic carcinomas and thymic neuroendocrine tumors compared to thymomas and demonstrated weak staining in a subset of morphologic mimics (21 squamous cell carcinomas, 6 pulmonary neuroendocrine tumors, 1 mesothelioma, 1 lymphoblastic lymphoma, and 1 granulosa cell tumor). With a H-score positive threshold of 75, the antibody had 100% specificity, and sensitivities of 92%, 56%, and 47% in thymomas, thymic neuroendocrine tumors, and thymic carcinomas respectively. The PAX1 antibody showed frequent geographic reduction in staining consistent with compromised antigenicity from variable formalin fixation. PAX1 IHC has a moderate-to-high sensitivity for thymic epithelial neoplasms; however, the wide staining variability and fixation effects may lead to difficulty with consistent interpretation. This marker is unlikely to supplant the role of PAX8 in diagnostic practice, but it may be a useful addition to immunohistochemistry panels when evaluating for thymic primary tumors.

Biocompatibility of three different root canal sealers, experimental study

OBJECTIVES

This study was assessed the biocompatibility of three different root canal sealers (Well-Root St, GuttaFlow Bioseal, and AH-Plus) following implantation in rat subcutaneous tissues, using histopathological immunohistochemical analysis.

METHODS

Four groups of eighty-four male rats each underwent subcutaneous dorsal implantation of a polyethylene tube, either empty or filled. Tissues were collected, fixed, and processed for histological analysis after 7, 15, and 30 d. Slides were photographed and digitally processed to identify lymphocytes and macrophages using Cluster of differentiation 3 (CD3) and cluster of differentiation 68 (CD68) markers, respectively. P was set at 0.05, when lymphocyte and macrophage infiltration was compared between groups and observation times using one-way analysis of variance (ANOVA).

RESULTS

Histopathological analysis of all groups revealed an inflammatory reaction followed by the emergence of a fibrous capsule after 7 days. After 30 days, the thickness of the fibrous capsule and the inflammatory response subsided. CD3 staining for immunohistochemical analysis revealed that the AH-Plus group had the highest mean percentage of lymphocyte infiltration at 7 and 15 days, followed by the Well-Root St, GuttaFlow Bioseal, and Control groups. After 30 days, no discernible difference was observed between the groups in terms of the mean percentage of lymphocyte infiltration. After 7, 15, and 30 days, there was a significant difference in the mean percentage of macrophage infiltration across the groups, as demonstrated by CD68 staining. After 7, 15, and 30 days, the AH-Plus group had the highest mean percentage of macrophage infiltration, followed by the Well-Root St. and GuttaFlow Bioseal groups, while the control group had the lowest mean percentage.

CONCLUSION

All observational periods showed minimal inflammatory reactions to GuttaFlow Bioseal. After subcutaneous tissue implantation in a rat model, the initial inflammatory reactions to Well-Root St and AH-Plus had abated by day 30, and all tested sealers had outstanding biocompatibility.

Immunocytochemistry for diagnostic cytopathology-A practical guide

Cytological specimens, which are obtained by minimally invasive methods, are an excellent source of diagnostic material. Sometimes they are the only material available for diagnosis as well as for prognostic/predictive markers. When cytomorphology is not straightforward, ancillary tests may be required for a definitive diagnosis to guide clinical management. Immunocytochemistry (ICC) is the most common and practical ancillary tool used to reach a diagnosis when cytomorphology is equivocal, to differentiate entities with overlapping morphological features, and to determine the cell lineage and the site of origin of a metastatic neoplasm. Numerous immunomarkers are available, and some are expressed in multiple neoplasms. To rule out entities within a differential diagnosis, the use of more than one marker, sometimes panels, is necessary. ICC panels for diagnostic purposes should be customised based on the clinical context and cytomorphology, and the markers should be used judiciously to preserve material for additional tests for targeted therapies in the appropriate setting. This review offers a practical guide for the use of ICC for diagnostic cytopathology, covering the most commonly encountered non-hematolymphoid diagnostic scenarios in various body sites.

A practical guide for ancillary studies in pulmonary cytologic specimens

Although most pulmonary cytologic specimens obtained by either exfoliation or fine needle aspirates can be reliably and accurately diagnosed based on pure morphologic criteria alone, a small proportion of cases require ancillary studies for either refining a diagnosis, for resolving a differential diagnosis or increasingly, for predictive purposes in primary lung carcinomas. This article aims to provide practical guidance on the use of common ancillary studies in pulmonary cytologic specimens. Cancer Cytopathol 2018;000:000-000. © 2018 American Cancer Society.

Cutaneous Metastases: A Review and Diagnostic Approach to Tumors of Unknown Origin

CONTEXT.—

Cutaneous metastases from a distant malignancy are a diagnostic challenge for pathologists. Secondary involvement of the skin by a metastatic process portends a much worse clinical prognosis than any primary cutaneous malignant mimickers. Immunohistochemical staining methods continue to evolve and are of paramount importance in diagnosis.

OBJECTIVE.—

To review the clinical, histopathologic, and immunohistochemical staining patterns for commonly encountered entities and discuss potential pitfalls in diagnosis. A practical guide useful in approaching cutaneous metastases of unknown primary is outlined.

DATA SOURCES.—

An extensive search and review of literature in PubMed was performed, processed, and condensed.

CONCLUSIONS.—

Cutaneous metastases have broad histopathologic patterns. They are nearly always dermal based, with an overall foreign appearance. They can be single papules/nodules or multiple in number, mimicking an inflammatory or infectious process. Ultimately, immunohistochemistry remains an essential diagnostic tool, and clinical correlation is paramount in the workup of these entities.

Classification and Pathology of Lung Cancer

Advancement in the understanding of lung tumor biology enables continued refinement of lung cancer classification, reflected in the recently introduced 2015 World Health Organization classification of lung cancer. In small biopsy or cytology specimens, special emphasis is placed on separating adenocarcinomas from the other lung cancers to effectively select tumors for targeted molecular testing. In resection specimens, adenocarcinomas are further classified based on architectural pattern to delineate tissue types of prognostic significance. Neuroendocrine tumors are divided into typical carcinoid, atypical carcinoid, small cell carcinoma, and large cell neuroendocrine carcinoma based on a combination of features, especially tumor cell proliferation rate.

Primary lung sarcoma treated with stereotactic ablative radiotherapy: a case report

Primary lung sarcoma (PLS) is an extremely rare, very aggressive malignancy. Surgical removal is considered the treatment of choice, and patients who have been given conventional radiotherapy have had inferior outcomes. This study is the first describing a case of PLS treated with stereotactic ablative radiotherapy (SABR), which precisely targets a small tumor with a markedly higher biologically effective dose than conventional radiotherapy. The patient was an 82-year-old man who was diagnosed with primary lung leiomyosarcoma based on radiology, pathology, and immunohistochemical examinations. The PLS was located in the right lower lobe and measured 2.5 cm. No regional nodal or distant organ metastasis was observed. He was inoperable medically. The SABR was performed using volumetric modulated arc therapy and a dose of 56 Gy in four fractions. Follow-up computed tomography 2 months after SABR revealed a complete tumor response. The toxicity was limited to mild respiratory symptoms. The patient is alive and has had no evidence of disease for 2 years. This study suggests that SABR can be a safe and effective treatment option for PLS.

Application of Immunohistochemistry in the Diagnosis of Pulmonary and Pleural Neoplasms

CONTEXT

- A vast majority of neoplasms arising from lung or pleura are initially diagnosed based on the histologic evaluation of small transbronchial, endobronchial, or needle core biopsies. Although most diagnoses can be determined by morphology alone, immunohistochemistry can be a valuable diagnostic tool in the workup of problematic cases.

OBJECTIVE

- To provide a practical approach in the interpretation and immunohistochemical selection of lung/pleura-based neoplasms obtained from small biopsy samples.

DATA SOURCES

- A literature review of previously published articles and the personal experience of the authors were used in this review article.

CONCLUSION

- Immunohistochemistry is a useful diagnostic tool in the workup of small biopsies from the lung and pleura sampled by small biopsy techniques.

Ribonucleic Acid In Situ Hybridization Is a More Sensitive Method Than Immunohistochemistry in Detection of Thyroid Transcription Factor 1 and Napsin A Expression in Lung Adenocarcinomas

CONTEXT

TTF-1 and napsin A immunomarkers have a crucial role in differentiating lung adenocarcinoma from lung squamous cell carcinoma and in identifying a primary lung adenocarcinoma when working on a tumor of unknown origin.

OBJECTIVES

To investigate the diagnostic sensitivity of ribonucleic acid in situ hybridization (RNAscope) in the detection of expression of these biomarkers in lung adenocarcinomas and to compare RNAscope to immunohistochemical techniques.

DESIGN

Both RNAscope and the immunohistochemical assays for TTF-1 and napsin A were performed on tissue microarray sections containing 80 lung adenocarcinomas and 80 lung squamous cell carcinomas. The RNAscope assay for both TTF-1 and napsin A was also performed on 220 adenocarcinomas from various organs.

RESULTS

The RNAscope assay for TTF-1 gave positive results in 92.5% (74 of 80) of the lung adenocarcinomas; in contrast, immunohistochemistry gave positive results in 82.5% (66 of 80) of those cases. The RNAscope assay for napsin A gave positive results in 90% (72 of 80) of lung adenocarcinomas; immunohistochemistry results were positive in 77.5% (62 of 80) of those cases. Napsin A expression was not seen in lung squamous cell carcinomas by either method. In contrast, TTF-1 expression was seen in 3.8% (3 of 80) (1(+)) and 10% (8 of 80) (1(+)) of the squamous cell carcinomas by immunochemistry and the RNAscope, respectively. All nonpulmonary adenocarcinoma results were negative for TTF-1 by the RNAscope assay.

CONCLUSIONS

Preliminary data suggest that RNAscope is superior to immunohistochemistry in detecting TTF-1 and napsin A expression in primary lung adenocarcinomas. Therefore, performing an RNAscope assay may be considered for both TTF-1(-) and napsin A(-) cases with a clinical suspicion of lung adenocarcinoma. The TTF-1 results should be interpreted with caution because a small percentage of squamous cell carcinomas can be focally positive by either assay.

Non-mesenchymal Mimics of Sarcoma

A variety of different non-mesenchymal neoplasms may mimic sarcoma, in particular sarcomatoid carcinoma and melanoma, but also mesothelioma and rarely some lymphomas. This article reviews the key clinical and histologic features of such neoplasms in different settings, along with the use of ancillary studies to help identify the tumor types most frequently misdiagnosed as sarcoma.