PDL-1 CPS (Sp 142,22C3 SP263) Genetech Test at Chughtai Lab

PD-L1 CPS Testing at Chughtai Lab

The advent of personalized medicine has revolutionized oncology, shifting the treatment paradigm from generalized cytotoxic chemotherapy to targeted therapies and immunotherapies. Among the most critical biomarkers guiding this transition is Programmed Death-Ligand 1 (PD-L1). PD-L1 is a transmembrane protein expressed on the surface of tumor cells and tumor-infiltrating immune cells. It interacts with the Programmed Death-1 (PD-1) receptor on T-cells, effectively sending an inhibitory signal that dampens the immune response and allows cancer cells to evade detection and destruction. To identify patients who are most likely to benefit from immune checkpoint inhibitors (ICIs), clinical laboratories perform immunohistochemistry (IHC) assays to evaluate PD-L1 expression. Chughtai Lab, a premier diagnostic institution in Pakistan, offers advanced PD-L1 testing using standardized, clinically validated antibody clones, including SP142, 22C3, and SP263, on the Genetech platform. This comprehensive testing determines the Combined Positive Score (CPS) and Tumor Proportion Score (TPS), providing oncologists with the precise diagnostic data required to formulate individualized, life-saving treatment plans.

Clinical Procedure: What to Expect

Patient Preparation

Unlike standard blood tests or imaging modalities, a PD-L1 immunohistochemistry test does not require direct physical preparation from the patient, such as fasting or medication cessation. Instead, the preparation centers entirely on the meticulous handling, preservation, and submission of the patient’s tumor tissue specimen. The primary specimen used for this analysis is a formalin-fixed paraffin-embedded (FFPE) tissue block, which is obtained during a previous surgical resection or core needle biopsy. To ensure the highest diagnostic accuracy, several pre-analytical parameters must be strictly managed:

• Cold Ischemia Time: The interval between the removal of the tissue from the patient’s body and its immersion in fixative must be kept to an absolute minimum, ideally under one hour, to prevent protein degradation.
• Fixation Duration: The tissue must be fixed in 10% neutral buffered formalin for a duration of 6 to 72 hours. Under-fixation or over-fixation can severely compromise the antigenicity of the PD-L1 protein, leading to false-negative or false-positive results.
• Specimen Submission: Patients or their attending clinical staff must submit the FFPE block along with the corresponding hematoxylin and eosin (H&E) stained slide and a detailed clinical history, including the primary tumor site, specimen type, and the specific immunotherapy agent being considered.

During the Procedure

Once the tumor tissue specimen is received at the advanced histopathology department of Chughtai Lab, it undergoes a highly standardized, automated immunohistochemical staining process. The laboratory utilizes state-of-the-art automated staining platforms, such as the Ventana BenchMark system, to minimize manual errors and ensure reproducibility. The procedure begins with microtomy, where a skilled histotechnologist cuts ultra-thin sections of the paraffin block, measuring approximately 4 to 5 micrometers in thickness, and mounts them onto positively charged glass slides. These slides are then subjected to deparaffinization and rehydration through a series of graded alcohols and water. Next, heat-induced epitope retrieval (HIER) is performed using specialized buffer solutions at controlled temperatures to unmask the PD-L1 antigens that were cross-linked during formalin fixation. The tissue sections are then incubated with the specific primary antibody clone requested by the oncologist: the 22C3 clone (often utilized for pembrolizumab eligibility), the SP142 clone (primarily used for atezolizumab in triple-negative breast cancer), or the SP263 clone (widely used for durvalumab and pembrolizumab). Following primary antibody incubation, a polymer-based detection system is applied, which binds to the primary antibody and introduces a horseradish peroxidase (HRP) enzyme. The addition of a chromogen substrate, typically diaminobenzidine (DAB), results in a visible brown precipitate at the site of PD-L1 antigen-antibody binding. The slides are counterstained with hematoxylin to visualize cellular nuclei, dehydrated, cleared, and coverslipped. A consultant histopathologist then examines the stained slides under a high-resolution light microscope to evaluate the staining patterns and calculate the appropriate score.

When is a PD-L1 CPS Test Performed?

Advanced Non-Small Cell Lung Cancer (NSCLC)

In patients diagnosed with advanced or metastatic non-small cell lung cancer, PD-L1 testing is a mandatory first-line diagnostic step. Oncologists request this test to determine whether the patient is a candidate for pembrolizumab as a monotherapy or in combination with chemotherapy. The pathologist calculates the Tumor Proportion Score (TPS), which is the percentage of viable tumor cells showing partial or complete membrane staining. A TPS of 50% or greater indicates high expression, making the patient eligible for first-line single-agent immunotherapy, which significantly improves overall survival compared to standard chemotherapy.

Triple-Negative Breast Cancer (TNBC)

Triple-negative breast cancer is an aggressive subtype of breast cancer that lacks estrogen, progesterone, and HER2 receptors. For patients with locally advanced or metastatic TNBC, immunotherapy combined with chemotherapy offers a vital therapeutic option. Physicians request PD-L1 testing using the SP142 clone to evaluate the percentage of tumor area occupied by PD-L1-positive tumor-infiltrating immune cells (ICs). If the immune cell staining is 1% or greater, the patient is eligible for atezolizumab treatment, which enhances the immune system’s ability to target and destroy the breast cancer cells.

Urothelial Carcinoma (Bladder Cancer)

Patients with advanced or metastatic urothelial carcinoma who are ineligible for cisplatin-based chemotherapy require PD-L1 testing to guide alternative treatment strategies. Pathologists utilize the 22C3 or SP142 clones to calculate the Combined Positive Score (CPS) or the immune cell (IC) score. A CPS of 10 or greater, or an IC score of 5% or greater, indicates that the patient is highly likely to respond to pembrolizumab or atezolizumab, respectively, providing an effective, less toxic therapeutic alternative for fragile patients.

Gastric and Gastroesophageal Junction (GEJ) Adenocarcinoma

For patients presenting with advanced, recurrent, or metastatic gastric or gastroesophageal junction adenocarcinoma, PD-L1 testing is critical for determining eligibility for immune checkpoint inhibitors. The pathologist calculates the Combined Positive Score (CPS), which incorporates the staining of both tumor cells and surrounding immune cells (lymphocytes and macrophages) relative to the total number of viable tumor cells. A CPS of 5 or greater, or in some clinical contexts 10 or greater, qualifies the patient for pembrolizumab or nivolumab in combination with chemotherapy, leading to improved progression-free survival.

Head and Neck Squamous Cell Carcinoma (HNSCC)

Patients with recurrent or metastatic head and neck squamous cell carcinoma that is refractory to platinum-based chemotherapy are candidates for immunotherapy. Oncologists request PD-L1 testing using the 22C3 clone to assess the Combined Positive Score (CPS). A CPS of 1 or greater indicates that the patient may benefit from pembrolizumab monotherapy, while a higher CPS often correlates with a more robust and durable clinical response, helping clinicians tailor the therapeutic regimen to the patient’s specific tumor microenvironment.

What Does a PD-L1 CPS Test Detect?

A comprehensive PD-L1 CPS and clone-specific immunohistochemical analysis at Chughtai Lab evaluates multiple cellular and tissue-level parameters. The test detects and reports the following key findings:

• Presence of adequate viable tumor cells, requiring a minimum of 100 cells for a valid evaluation.
• Absence of adequate tumor cells, rendering the specimen unsatisfactory for scoring.
• Tumor Proportion Score (TPS) expressed as a percentage from 0% to 100%.
• Combined Positive Score (CPS) calculated as a numerical value up to a maximum of 100.
• Partial or complete linear membrane staining of viable tumor cells.
• Cytoplasmic staining of tumor cells, which is noted but excluded from the official score.
• PD-L1 expression on tumor-infiltrating lymphocytes (TILs), including helper and cytotoxic T-cells.
• PD-L1 staining on macrophages within the tumor nests and adjacent stroma.
• PD-L1 staining on dendritic cells and other antigen-presenting cells.
• Percentage of tumor area occupied by PD-L1-positive immune cells (specifically for the SP142 clone).
• Staining intensity categorized as weak (1+), moderate (2+), or strong (3+).
• Intratumoral heterogeneity, where different areas of the tumor exhibit varying levels of PD-L1 expression.
• Intertumoral heterogeneity, comparing expression between primary and metastatic sites.
• Presence of background non-specific staining or artifactual staining.
• Edge artifacts, where tissue margins show artificial staining due to drying or preparation.
• Staining in areas of necrosis, which is excluded from the final score.
• Staining of normal adjacent tissue, serving as an internal reference.
• Positive control tissue validation, confirming the run’s technical success.
• Negative control tissue validation, ensuring the absence of non-specific binding.
• Melanin pigment interference in melanocytic lesions, requiring special clinical consideration.
• Decalcification artifacts in bone biopsy specimens, which may reduce antigenicity.
• Specific membrane staining patterns associated with the 22C3 clone.
• Specific immune cell staining patterns associated with the SP142 clone.
• High-affinity membrane staining associated with the SP263 clone.
• Preservation of tissue morphology, ensuring the structural integrity of the specimen.
• Presence of inflammatory aggregates in the tumor stroma.
• Staining of vascular endothelial cells, which is excluded from scoring.
• Staining of stromal fibroblasts, which is excluded from scoring.

Turnaround Time and Report Access at Chughtai Lab

At Chughtai Lab, we understand that timely diagnostic results are critical for cancer patients awaiting treatment decisions. The turnaround time for specialized immunohistochemistry tests, such as the PD-L1 CPS (SP142, 22C3, SP263) assay, is typically 5 to 7 working days. This timeframe allows our pathology team to perform precise tissue processing, automated staining, quality control checks, and detailed microscopic evaluation. Once the report is finalized by our consultant histopathologist, patients and their oncologists can access the results instantly through the Chughtai Lab mobile application or our secure online patient portal. Physical copies of the reports can also be collected from any of our convenient collection centers located across Pakistan.

PD-L1 CPS Test Findings Overview

Structure / Parameter Evaluated	Normal Findings	Possible Abnormal Findings
Viable Tumor Cell Count	Adequate cellularity (greater than or equal to 100 viable tumor cells)	Inadequate cellularity (less than 100 viable tumor cells), preventing reliable scoring
PD-L1 Clone 22C3 Expression	No staining or TPS less than 1% / CPS less than 1	TPS greater than or equal to 1% or 50%; CPS greater than or equal to 1, 5, 10, or 20
PD-L1 Clone SP142 Expression	Immune cell (IC) staining less than 1% of tumor area	Immune cell (IC) staining greater than or equal to 1% or 5% of tumor area
PD-L1 Clone SP263 Expression	No membrane staining or low expression levels	Moderate to strong membrane staining in tumor and immune cells
Combined Positive Score (CPS)	CPS less than 1 (negative for PD-L1 expression)	CPS greater than or equal to 1, 5, or 10 (positive for PD-L1 expression)
Tumor Proportion Score (TPS)	TPS less than 1% (no significant tumor cell expression)	TPS of 1% to 49% (low positive) or greater than or equal to 50% (high positive)
Tissue Fixation Quality	Optimal fixation with preserved cellular and membrane morphology	Under-fixation or over-fixation leading to antigen loss or high background noise
Control Tissue Staining	Expected positive staining in external control tissue (e.g., tonsil or placenta)	Failure of control staining, indicating a technical run failure requiring re-testing

Note: Diagnostic findings should always be interpreted by a qualified healthcare professional together with the patient’s symptoms, medical history, physical examination, laboratory investigations, previous imaging studies, and other relevant clinical information. Additional investigations or specialist consultation may be recommended depending on the findings.

Why Choose Chughtai Lab for PD-L1 CPS Testing?

• Experienced healthcare professionals and board-certified histopathologists specializing in oncopathology.
• Patient-focused care prioritizing accurate, timely, and reliable diagnostic reporting.
• Quality diagnostic services utilizing state-of-the-art automated immunohistochemistry platforms.
• Professional reporting with detailed scoring metrics (CPS, TPS) tailored to specific companion diagnostic clones.
• Modern diagnostic approach integrating molecular pathology and advanced companion diagnostics.
• Comfortable environment and highly supportive staff at all collection centers.
• Convenient locations across Pakistan, ensuring easy access for patients nationwide.
• Commitment to accurate diagnosis through rigorous internal quality control and external proficiency testing.