• Minimum of 100 viable tumor cells must be present for evaluation
• Scoring in necrotic areas should be avoided
• Any degree of staining intensity (1+ to 3+) counts towards scoring
• Scoring is tumor site dependent
• Staining can be present in both immune cell (IC) and tumor cell (TC) components
• Tumor cells
  • Only membrane staining should be evaluated
  • Partial or complete membrane staining is included
  • Cytoplasmic staining is not included
• Immune cells
  • Membrane and cytoplasmic staining are often indistinguishable due to high N:C ratio
  • Therefore, both membrane and cytoplasmic staining of inflammatory cells are included
  • Only staining in lymphocytes and macrophages is counted
  • Staining in neutrophils, eosinophils and plasma cells is not counted
• Recommended control tissue: benign human tonsil

Non-small cell lung carcinoma (NSCLC)

• Evaluated using a tumor proportion score (TPS)
  • TPS is the percentage of viable tumor cells showing partial or complete membrane staining (≥ 1+) relative to all viable tumor cells present in the sample
  • Specimen should be considered to have PDL1 expression if TPS ≥ 1% and high PDL1 expression if TPS ≥ 50%
  
  

  TPS =	Number of PDL1 positive tumor cells	× 100
  	Total number of PDL1 positive + PDL1 negative tumor cells

  
  
• Divided into 3 levels:
  • TPS < 1%: no PDL1 expression
  • TPS 1 - 49%: PDL1 expression
  • TPS ≥ 50%: high PDL1 expression

Cervical carcinoma

• Expression is determined by using combined positive score (CPS)
  • CPS is the number of PDL1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100
  • Specimen should be considered to have PDL1 expression if CPS is ≥ 1
  • Cells in the numerator include all viable invasive tumor cells and mononuclear immune cells directly associated with the response to the tumor (lymphocytes and macrophages within tumor nests and adjacent supporting stroma); adjacent mononuclear immune cells are defined as being within the same 20x field as the tumor
  
  

  CPS =	Number of PDL1 staining cells (tumor cells, lymphocytes, macrophages)	× 100
  	Total number of viable tumor cells

  
  
• CPS value can be > 100 but the maximum value reported is 100
• Divided into 2 groups:
  • CPS < 1: no PDL1 expression
  • CPS ≥ 1: PDL1 expression

Head and neck squamous cell carcinoma (HNSCC)

• Expression is determined by using combined positive score (CPS)
  • CPS is the number of PDL1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100
  • PDL1 expression (CPS ≥ 1) is used to inform patient eligibility for first line therapy with pembrolizumab
  • Cells in the numerator include all viable invasive tumor cells and mononuclear immune cells directly associated with the response to the tumor (lymphocytes and macrophages within tumor nests and adjacent supporting stroma); adjacent mononuclear immune cells are defined as being within the same 20x field as the tumor
• Divided into 3 groups:
  • CPS < 1: no PDL1 expression
  • CPS ≥ 1: PDL1 expression
  • CPS ≥ 20: PDL1 expression*
• *PDL1 expression level CPS ≥ 20 may be of interest to treating physicians but does not determine eligibility for first line therapy

Esophageal squamous cell carcinoma (ESCC)

• Expression is determined by using combined positive score (CPS)
  • CPS is the number of PDL1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100
  • Specimen should be considered to have PDL1 expression if CPS is ≥ 10
  • Cells in the numerator include all viable invasive tumor cells and mononuclear immune cells directly associated with the response to the tumor (lymphocytes and macrophages within tumor nests and adjacent supporting stroma); adjacent mononuclear immune cells are defined as being within the same 20x field as the tumor
• Divided into 2 groups:
  • CPS < 10: no PDL1 expression
  • CPS ≥ 10: PDL1 expression

Triple negative breast cancer (TNBC)

• Expression is determined by using combined positive score (CPS)
  • CPS is the number of PDL1 staining cells (tumor cells, lymphocytes, macrophages) divided by the total number of viable tumor cells, multiplied by 100
  • Specimen should be considered to have PDL1 expression if CPS is ≥ 10
• Divided into 2 groups:
  • CPS < 10
  • CPS ≥ 10

Urothelial carcinoma

• Following the FDA's Oncologic Drugs Advisory Committee (ODAC) meeting (2021), the approved pembrolizumab indication was updated for the treatment of patients with locally advanced or metastatic urothelial carcinoma who are not eligible for any platinum containing chemotherapy; due to this update, PDL1 testing to determine eligibility of urothelial carcinoma patients for treatment with pembrolizumab is no longer indicated

References: Agilent: PD-L1 IHC 22C3 pharmDx Overview [Accessed 2 February 2023], Agilent: PD-L1 IHC 22C3 pharmDx Interpretation Manual - NSCLC [Accessed 2 March 2023], Dako: PD-L1 IHC 22C3 pharmDx Interpretation Manual - Esophageal Squamous Cell Carcinoma (ESCC) [Accessed 16 January 2023]

Contributed by Gary Tozbikian, M.D.

A PDL1 (22C3) immunostain is shown above. Which of the following statements regarding PDL1 (22C3) is correct?

1. PDL1 (22C3) is the FDA approved companion diagnostic assay for nivolumab
2. In advanced / metastatic triple negative breast cancer, PDL1 (22C3) is determined by using combined positive score (CPS), with a positive score cutoff of CPS ≥ 1
3. In non-small cell lung carcinoma, PDL1 (22C3) is determined by using combined positive score, with a positive score cutoff of CPS ≥ 10
4. In esophageal squamous cell carcinoma, PDL1 (22C3) is determined by using tumor proportion score (TPS), with a positive score cutoff of TPS ≥ 1%
5. In non-small cell lung carcinoma, scoring of PDL1 (22C3) is only evaluated in the tumor cell component

E. In non-small cell lung carcinoma, scoring of PDL1 (22C3) is only evaluated in the tumor cell component. Answer A is incorrect because PDL1 (22C3) is the FDA approved companion diagnostic assay for pembrolizumab. Answers B and D are incorrect because in triple negative breast cancer and esophageal squamous cell carcinoma, 22C3 is scored using combined positive score, with a cutoff of CPS ≥ 10. Answer C is incorrect because in non-small cell lung carcinoma, 22C3 is scored using a tumor proportion score. Tumor proportion score is scored by evaluating the PDL1 expression in the tumor cell component only.

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Reference: PDL1 22C3