PD-L1 immunohistochemical testing: A review with reference to cytology specimens
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Published on: September 25, 2018
Lester J Layfield1, Tao Zhang2, Magda Esebua1
1Department of Pathology and Anatomical Sciences, University of Missouri, Columbia, Missouri, USA.
Background:
Immunotherapy based on disruption of the PD-1/PD-L1 axis is standard of care for many high stage malignancies including melanomas, non-small cell carcinomas of the lung, triple negative breast carcinomas, and squamous cell carcinomas of the head and neck. Eligibility for immunotherapy requires immunohistochemical assessment of PD-L1 expression. Currently, many high stage malignancies are diagnosed by cytology and cytologic material is the only specimen available for ancillary testing. Formal guidelines do not currently exist defining the optimal specimen type, antibody to be used or the best scoring system for cytologic material. Significant information has been published for PD-L1 testing of pulmonary specimens but much less data exists for the reproducibility, accuracy and best practices for material obtained from other body sites and types of malignancy.
Methods:
We searched the PubMed data base for manuscripts relating to PD-L1 testing of cytologic specimens. The search period was between 2016 and 2022. The search terms used were PD-L1, cytology, FNA, immunotherapy, immunohistochemistry, immunocytochemistry, cytology-histology correlation. Cross referencing techniques were used to screen for the most relevant manuscripts. The abstracts of these were then reviewed for final data collection and analysis.
Results:
A total of 86 studies were identified conforming to study relevancy. These were reviewed in their entirety by two authors (LJL, TZ) for extraction of data. The majority of studies involved pulmonary specimens (79) with three relating to PD-L1 testing of head and neck cytologic specimens and one each for PD-L1 testing of cytology specimens from melanomas, pancreas, pleural fluids, and triple negative breast carcinomas. While smears could be used, most studies found cell blocks optimal for testing.
Summary:
Currently, four drugs are approved for immunotherapy based on PD-L1 status. These drugs require specific antibody clones as well as scoring systems. Scoring systems and cut points vary with the type of neoplasm being treated. Cytology specimens from the lung, head and neck and melanomas can all be used for PD-L1 testing with good agreement with corresponding histology specimens.
Insights
PD-L1 testing on cytology specimens is crucial for immunotherapy eligibility in various cancers. Cell blocks are optimal for this testing, showing good agreement with histology, especially for lung, head and neck, and melanoma samples.
Area of Science:
- Oncology
- Immunology
- Pathology
Background:
- Immunotherapy targeting the PD-1/PD-L1 axis is a standard treatment for advanced cancers.
- PD-L1 expression assessment via immunohistochemistry is required for immunotherapy eligibility.
- Cytologic specimens are often the only available material for ancillary testing, yet guidelines for PD-L1 assessment are lacking.
Approach:
- A systematic literature search of PubMed was conducted for studies on PD-L1 testing in cytologic specimens from 2016 to 2022.
- Search terms included PD-L1, cytology, FNA, immunotherapy, immunohistochemistry, immunocytochemistry, and cytology-histology correlation.
- Relevant manuscripts were screened, and data were extracted for analysis.
Key Points:
- 86 studies were reviewed, with most focusing on pulmonary specimens.
- PD-L1 testing on cytology specimens from lung, head and neck, melanoma, pancreas, pleural fluids, and triple-negative breast carcinoma were included.
- Cell blocks were found to be optimal for PD-L1 testing compared to smears.
Conclusions:
- Cytology specimens from lung, head and neck, and melanomas can be reliably used for PD-L1 testing.
- Results show good agreement between PD-L1 testing on cytology and corresponding histology specimens.
- Standardized guidelines for PD-L1 testing on cytologic material are needed.
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