By Andre L. Moreira, MD
Posted: April 1, 2019
Most of the progress in thoracic oncology is in the treatment of patients with NSCLC. The determination of subtypes of NSCLC, namely adenocarcinoma and squamous cell carcinoma, is directly linked with chemotherapy regimens and the search for targetable molecular alterations. The 2015 World Health Organization Classification of Lung Tumors first introduced the importance of immunohistochemical (IHC) stains as an ancillary test to separate NSCLC subtypes, especially in small biopsy and cytologic samples that constitute most specimens for the diagnosis of lung cancer. One important consideration is the need to balance tissue use for diagnostic and molecular testing when more stains are added to the panels.
Although the classification of lung cancer remains based on histologic features, IHC is recommended in cases with no morphologic evidence of differentiation, thus improving diagnostic accuracy. However, interpretation of IHC can be challenging. The pathologists must be aware of the many pitfalls that can involve selection of antibody panels, clones, and staining patterns.
The IASLC Pathology Committee undertook a comprehensive project to provide a consensus guideline for IHC use for lung cancer classification. Members of the Committee were asked to raise questions concerning IHC use in their daily practice. The questions were not limited to the subclassification of NSCLC but rather were inclusive of all possible scenarios in which IHC should be used in lung cancer pathology, including best markers to distinguish NSCLC subtypes, use of IHC for the diagnosis of neuroendocrine tumors, uncommon subtypes, and distinction of primary pulmonary tumors from metastatic cancers to the lung.
Most clinicians experience frustration with cytologic material, and often these useful specimens are left out of clinical trials. The use of cytology specimens for IHC is addressed in this study and will be expanded under a study from the cytology working group of the IASLC Pathology Committee. Their additional observations and recommendations will be the subject of a separate publication.
The results of this project were summarized into 11 practical core questions that were then answered by literature search and consensus discussions within the group (Table). The results are now published in the Journal of Thoracic Oncology.1 The article by the IASLC Pathology Committee provides guidelines and quick, useful explanations for pathologists and the larger lung cancer healthcare provider community concerning the best use of IHC encountered in daily routine for the diagnosis of lung carcinoma. ✦
About the Author: Dr. Moreira is a professor in the Department of Pathology, director of the Cardiopulmonary Pathology Fellowship Program, director of Surgical Pathology, director of NYU Center for Biospecimen Research and Development, and director of Pulmonary Pathology at NYU Langone.
1. Yatabe Y, Dacic S, Borczuk AC, et al. Best Practices Recommendations for Diagnostic Immunohistochemistry in Lung Cancer. J Thorac Oncol. 2019;14(3):377-407.