Editors: Rouzan Karabakhtsian, MD, PhD, professor of pathology and director of the Women’s Health Pathology Fellowship, Albert Einstein College of Medicine, Montefiore Medical Center, Bronx, NY; S. Emily Bachert, MD, associate pathologist, Brigham and Women’s Hospital, Boston; Amarpreet Bhalla, MD, assistant professor of pathology, Albert Einstein College of Medicine, Montefiore Medical Center; Divya Sharma, MD, associate professor, Department of Pathology and Laboratory Medicine, University of Cincinnati Medical Center; and Paula Toro, MD, pathology resident, Cleveland Clinic.
Evaluation of claudin-18.2 IHC in gastric and gastroesophageal junction adenocarcinomas to direct therapy
April 2025—Claudin-18.2 (CLDN18.2) is a biomarker for locally advanced or metastatic gastric and gastroesophageal junction adenocarcinomas that may respond to targeted therapy with monoclonal antibodies directed against CLDN18.2. Despite successful testing in clinical trials, no practical testing guidelines had been proposed at the time the authors’ article featured herein was published. Several preanalytical and analytical variables may interfere with CLDN18.2 staining interpretation. Therefore, the authors provided practical guidance on CLDN18.2 testing and scoring in gastric and gastroesophageal junction adenocarcinomas. They established criteria pertaining to sample characteristics, analytical requirements, staining evaluation, and reporting. Sample requirements included at least six tissue fragments on biopsy or 50 viable malignant cells (preferably 100 in effusion cytology). Because CLDN18.2 expression is highly concordant in matched primary and metastatic lesions, the most suitable sample should be used for testing. Analytical requirements included performing CLDN18.2 staining on formalin-fixed, paraffin-embedded tissues and using isoform-specific or pan-claudin-18-specific antibodies. Positive staining for CLDN18.2 is defined as crisp membranous staining—complete, basolateral, or lateral. Any granular membranous staining, cytoplasmic staining, or nuclear staining is considered negative. Staining intensity is scored between 0 and 3+ (absent, 0; weak, 1+; moderate, 2+; strong, 3+). A 3+ intensity is defined as strong brown immunoreactivity with an evident chicken wire distribution at low power (×5 objective) when 3,3’ diaminobenzidine is used as a chromogen. A 2+ membranous staining is visible using a ×10 objective and a 1+ staining using a ×20 objective. Normal foveolar epithelium is a valuable internal control and serves as the maximal 3+ staining intensity. Moderate to strong (2+/3+) positive membrane staining in 75 percent or more of tumor cells is the proposed cutoff for clinical use of the anti-CLDN18.2 monoclonal antibody zolbetuximab. The authors advocate that the pathology report incorporate type of specimen (biopsy or surgical), site of sampling (primary or metastatic), tissue fixation time, sample adequacy, antibody clone and IHC stainer used, identification as a laboratory-developed or companion diagnostic test, and test results reported as the percentage of cells with moderate to strong (2+/3+) membranous immunoreactivity and as positive or negative according to the cutoff of 75 percent or more of membranous positive (2+/3+) adenocarcinoma cells.
Fassan M, Kuwata T, Matkowskyj KA, et al. Claudin-18.2 immunohistochemical evaluation in gastric and gastroesophageal junction adenocarcinomas to direct targeted therapy: A practical approach. Mod Pathol. 2024;37(11). doi.org/10.1016/j.modpat.2024.100589
Correspondence: Dr. Matteo Fassan at [email protected]
Banking tissue before initial H&E section as a source of DNA for molecular testing
Small biopsies are used for histologic, immunophenotypic, cytogenetic, molecular genetic, and other ancillary studies. Occasionally, this diagnostic tissue is exhausted before molecular testing can be performed. The authors conducted a study to investigate a simple protocol for banking DNA for molecular studies using tissues trimmed off prior to creating the initial hematoxylin and eosin-stained section. Mock biopsies of lung adenocarcinomas, benign testes, and B-cell lymphomas were constructed from biobank blocks. The simulated biopsies were assessed via epidermal growth factor receptor (EGFR) p.L858R droplet digital polymerase chain reaction (PCR), Biomed B-cell clonality testing by PCR, or a custom next-generation sequencing panel for lymphomas. For each mock cancer biopsy, DNA amounts and molecular test results from the “trimmings” were compared with data from corresponding molecular samples acquired via a standard clinical protocol. The data showed that although the trimmings usually contained less DNA than the standard samples, both generally had sufficient DNA for testing and produced essentially identical molecular results. A single benign testes trimmings sample showed low-level carryover contamination on droplet digital PCR testing. The authors concluded that tissue trimmings that were banked using the study protocol demonstrated value as potential alternative samples for molecular testing.
Sabatini P, Ta R, Peralta M, et al. Tissue prior to the initial hematoxylin-eosin section demonstrates value as an alternative source of DNA for molecular testing. Arch Pathol Lab Med. 2024. doi.org/10.5858/arpa.2024-0222-OA
Correspondence: Dr. Daniel Xia at [email protected]
Inflammatory giant cell carcinoma of lung: a clinicopathologic, IHC, and next-generation sequencing study
Pleomorphic carcinoma encompasses primary lung sarcomatoid tumors that present with spindled or giant neoplastic tumor cells, or both. These tumors may be variably diagnosed as spindle cell carcinoma or giant cell carcinoma, depending on the proportions of cell types identified within each tumor (10 percent of each component needed). The authors studied 14 cases of primary sarcomatoid lung carcinoma that were characterized by a distinctive histological appearance in which the majority of the tumor consisted of poorly differentiated sheets of large discohesive tumor cells embedded in a dense inflammatory stromal background. They described the clinicopathologic, IHC, and molecular genetic features of these tumors and reviewed the related literature. The tumors occurred in seven men and seven women (mean age, 56 years). They predominantly affected the upper lobes and measured 1.3 to 9 cm in greatest diameter (mean, 4.6 cm). Morphologically, the tumor cells were characterized by large pleomorphic nuclei with prominent nucleoli, ample cytoplasm, and frequent abnormal mitoses. They were surrounded by a dense inflammatory cell infiltrate often associated with emperipolesis. IHC stains were positive in the tumor cells for cytokeratin AE1/AE3 and CK8/18 and negative for markers of squamous (p40, CK5/6) or glandular (TTF-1, napsin) differentiation. Next-generation sequencing on the Oncomine precision assay (Thermo Fisher Scientific) showed that the most common abnormalities were TP53 mutations (nine cases) and AKT1 amplification (eight cases), followed by KRAS (four cases) and MAP2K1/2 mutations (four cases). Clinical follow-up was available for 13 patients. Eight of those patients died from their tumors at six months to eight years (mean, 2.7 years); three patients were alive and free of disease between four and six years; and two patients had metastases when last seen but were lost to follow-up. This study, which focused on tumors that fit the World Health Organization definition of giant cell carcinoma, calls attention to distinctive features of these tumors that set them apart histologically from other sarcomatoid subtypes of lung carcinoma.
Suster DI, Mackinnon AC, Ronen N, et al. Inflammatory giant cell carcinoma of the lung: clinicopathologic, immunohistochemical, and next-generation sequencing study of 14 cases. Am J Surg Pathol. 2024;48(10):1215–1223.
Correspondence: Dr. David I. Suster at [email protected]