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MEL (Melanoma) Scoring System for PD-L1 Expression in Malignant Melanoma

Description

Daud et al evaluated patients with malignant melanoma using the expression of PD-L1 by immunohistochemical staining. This can help to identify a patient who may benefit from targeted therapy with pembrolizumab. The authors are from multiple institutions in the United States, Canada, Australia and France.


 

PD-L1 is Programmed Death Ligand 1.

 

Patient selection: malignant melanoma

 

Immunohistochemical stain: PD-L1 IHC 22C3 pharmDx (Dako North America)

 

Cells evaluated:

(1) tumor cells

(2) mononuclear inflammatory cells intercalated with tumor cells (exclude inflammatory cells within the stroma)

 

Target: membrane staining

Membrane Staining

MEL Score

none

0

less than 1%

1

1 to 9.9%

2

10 to 32.9%

3

33 to 65.9%

4

>= 66%

5

 

Interpretation:

• A MEL score >= 2 (1% or more) is considered positive.

• The higher the MEL score the better the objective response and longer progression-free survival (PFS).

• About 10% of patients with negative MEL staining will respond to pembrolizumab therapy.

 

Performance:

• Scoring can be arbitrary and there is intra- and inter-observer variation.

• One issue is what is being counted. Is a cell with any staining of its membrane counted? Or is it a percent of the total membrane surface of all eligble cells?

 


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