The 28-8 clone is a distinct PD-L1 antibody used in immune-oncology workups, and understanding its staining principle prevents the common error of mixing it up with other clones. This service delivers a tumor-cell PD-L1 score using the 28-8-specific algorithm that pathologists and prescribers rely on. Because scoring thresholds are clone-specific, the antibody named on the report is as important as the percentage printed next to it.
On a formalin-fixed section, the 28-8 antibody localizes PD-L1 membrane expression; automated staining and a peroxidase substrate produce a visible signal. A pathologist then counts the share of tumor cells with partial or complete membrane staining to derive the tumor proportion score. Internal controls confirm staining quality, and only validated lots are used to keep signal interpretation stable. Weak or absent control staining blocks sign-out, which protects against falsely low scores reaching the clinic.
28-8 scoring is requested where that specific clone is the intended assay, often alongside tissue availability for a single-slide read. It supports immune-therapy discussion when the prescriber needs a clone-specific, audit-ready result. Labs document the scoring version so a result generated this quarter stays comparable to one generated later in the same program.
A four micron FFPE cut with matched H&E is preferred. Equivocal staining is repeated, and the report records the TPS with the clone named. A second review resolves borderline cases. Turnaround is tracked so the immune-oncology team can time the therapy decision against the scan and the performance status.
Slides travel ambient in a protective sleeve; heat and humidity are limited to preserve antigen signal. Distributors receive calibration slides so offshore readings track the reference site. Lot-to-lot staining checks are archived, giving cross-border partners confidence that a 28-8 score means the same thing everywhere.
Q: What distinguishes 28-8 from 22C3 staining? A: They are different antibodies with different thresholds, so scores are not interchangeable. The clone must match the indication's validated assay before use.
Q: How is the tumor proportion score derived? A: By counting tumor cells with membrane staining after validated automated IHC. Only tumor cells are scored, not immune or stromal cells, per the algorithm.
Q: Can one slide serve multiple PD-L1 clones? A: Typically no; each clone needs its own stained section for a valid score. Ordering the correct clone up front avoids a repeat biopsy or recut.
The 28-8 clone is a distinct PD-L1 antibody used in immune-oncology workups, and understanding its staining principle prevents the common error of mixing it up with other clones. This service delivers a tumor-cell PD-L1 score using the 28-8-specific algorithm that pathologists and prescribers rely on. Because scoring thresholds are clone-specific, the antibody named on the report is as important as the percentage printed next to it.
On a formalin-fixed section, the 28-8 antibody localizes PD-L1 membrane expression; automated staining and a peroxidase substrate produce a visible signal. A pathologist then counts the share of tumor cells with partial or complete membrane staining to derive the tumor proportion score. Internal controls confirm staining quality, and only validated lots are used to keep signal interpretation stable. Weak or absent control staining blocks sign-out, which protects against falsely low scores reaching the clinic.
28-8 scoring is requested where that specific clone is the intended assay, often alongside tissue availability for a single-slide read. It supports immune-therapy discussion when the prescriber needs a clone-specific, audit-ready result. Labs document the scoring version so a result generated this quarter stays comparable to one generated later in the same program.
A four micron FFPE cut with matched H&E is preferred. Equivocal staining is repeated, and the report records the TPS with the clone named. A second review resolves borderline cases. Turnaround is tracked so the immune-oncology team can time the therapy decision against the scan and the performance status.
Slides travel ambient in a protective sleeve; heat and humidity are limited to preserve antigen signal. Distributors receive calibration slides so offshore readings track the reference site. Lot-to-lot staining checks are archived, giving cross-border partners confidence that a 28-8 score means the same thing everywhere.
Q: What distinguishes 28-8 from 22C3 staining? A: They are different antibodies with different thresholds, so scores are not interchangeable. The clone must match the indication's validated assay before use.
Q: How is the tumor proportion score derived? A: By counting tumor cells with membrane staining after validated automated IHC. Only tumor cells are scored, not immune or stromal cells, per the algorithm.
Q: Can one slide serve multiple PD-L1 clones? A: Typically no; each clone needs its own stained section for a valid score. Ordering the correct clone up front avoids a repeat biopsy or recut.
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