Scores for PDL-1 Expression

1. Tumor Proportion Score (TPS): 

The percentage of viable tumor cells showing partial or complete membrane staining for PD-L1, relative to all viable tumor cells in the sample.

Formula:

$$\text{TPS} = \frac{\text{PD-L1 positive tumor cells}}{\text{total viable tumor cells}} \times 100\%$$

Interpretation example: TPS 10% → 10% of tumor cells express PD-L1.

2. Combined Positive Score (CPS):

The number of PD-L1–staining cells (tumor cells + lymphocytes + macrophages) divided by the total number of viable tumor cells, multiplied by 100.

Formula:

$$\text{CPS} = \frac{\text{PD-L1 positive tumor cells + PD-L1 positive immune cells}}{\text{total viable tumor cells}} \times 100$$

Interpretation example: CPS 20 → there are 20 PD-L1–positive cells (tumor + immune) for every 100 tumor cells.

3. Tumor Area Positivity (TAP):

The percentage of the total tumor area (tumor cells + associated stroma) showing PD-L1–positive staining, regardless of cell type. Measures area, not cell count.

Formula:

$$\text{TAP} = \frac{\text{PD-L1 positive area (tumor + stroma)}}{\text{total tumor area}} \times 100\%$$

Interpretation example: TAP ≥ 10% → at least 10% of the tumor area (tumor cells or immune cells) is PD-L1–positive.