1. PD-L1 Expression in Metastatic Cutaneous Squamous Cell Carcinomas Nathaniel A. Slater, MD1, James Tidwell, MD2, George Sonnier, MD2, Paul Googe, MD1,3 1Department of Dermatology, University of North Carolina School of Medicine, Chapel Hill, NC, USA 2University of Louisville Division of Dermatology, Louisville, KY, USA 3Knoxville Dermatopathology Laboratory, Knoxville, TN, USA
Introduction: PD-1 / PD-L1 Axis
Assessing PD-L1 Expression in cSCC
PD-L1 Expression in Metastatic cSCC
Collated findings from 15 metastatic SCC cases, in comparison with 40 primary cutaneous SCC cases as previously published
Negative PD-L1 expression
To date, several case reports have demonstrated response to therapy targeting the PD1 / PD-L1 axis of regionally advanced or metastatic cutaneous squamous cell carcinoma not amenable to surgical treatment modalities [cite]. In some cases, PD-1 / PD-L1 checkpoint blockade has also resulted in durable remissions in other cancer types including NSMLC. Currently, 2 PD-1 directed antibodies are approved for treatment of certain advanced malignancies; others are in development. Immunotherapies targeting the PD-1/PD-L1 axis appear to have less toxicity than CTLA-4 blockade.
PD-L1 is a transmembrane protein involved in regulation of cellular and humoral immune responses. PD-L1 is mainly expressed on antigen presenting cells, activated T and B cells, placenta. PD-1 (receptor) is broadly expressed on activated lymphoid cells. It is also highly expressed on regulatory T cells, and over-expressed on exhausted T cells. Interaction of PD-L1 with receptor PD-1 helps regulate T cell activation and tolerance during pregnancy, tissue allografts, and in autoimmune disease.
H&E, low power
PD-L1, low power
PD-L1 Expression in Viable Tumor Cells of 40 Primary Cutaneous SCCs and 15 Loco-regional Metastatic Cutaneous SCCs
PDL Expression
Low Risk SCCs
(n = 20)
High Risk SCCs
Metastatic SCCs
(n = 15)
PD-L1 Tumor
Proportion Score
N (%)
Negative
16 (80)
6 (30)
4 (27)
Low
4 (20)
12 (60)
9 (60)
High
0 (0)
2 (10)
2 (13)
Mean % of tumor cells PD-L1 positive (range)
2% (0 – 25)
20% (0 – 90)
24% (4 – 90)
Difference in Tumor Proportion Score categories, Low Risk vs Metastatic SCCs: p = (Fisher’s exact test)
No Expression: Partial or complete cell membrane staining (≥ 1+) in < 1% of viable tumor cells
Left: 1.9cm grade 2 SCC invasive to subcutaneous fat, 7.7mm depth. No PD-L1 expression observed in constitutive skin structures. There is only focal reactivity for PD-L1 in tumor-infiltrating lymphocytes (TILs, arrow); TILs expressed at least focal PD-L1 in nearly all cases
H&E, high power
PD-L1, high power
Gianchecchi et al.
PD-1 predominantly regulates effector functions of activated T cells. PD-1/PD-L1 interaction inhibits proliferation and cytotoxic program of CD8+ T cells, and promotes regulatory T cell differentiation. PD-1 expression on CD8+ T cells has been associated with functional impairment of tumor infiltrating lymphocytes in HCC, melanoma, Hodgkin’s, and RCC.
Metastatic case with low expression of PD-L1 (low and high power)
Low PD-L1 expression
H&E, low power
PD-L1, low power
Low Expression: Partial or complete cell membrane staining (≥ 1+) in 1–49% of viable tumor cells
Left: 2.4cm grade 2 SCC invasive to subcutaneous fat, 7.2mm depth. Low PD-L1 expression visible in approximately 40% of carcinoma cells, mostly present at periphery of tumor.
At higher power, PD-L1 reactivity is complete along the tumor cell membranes and of moderate intensity
Metastatic cutaneous SCC with high expression of PD-L1 (H&E and immunostain)
Malignancies can hijack this pathway to evade host anti-tumor
response. PD-L1 expression has been found on some tumors such as melanoma, DLBCL, Hodgkin’s, triple negative breast ca, and carcinomas of the GI, GU, and pulmonary tracts. PD-L1 in pulmonary adenocarcinoma has been shown to correlate with histologic subtypes portending poorer prognosis. Overall however, the association between PD-L1 expression and prognosis is unclear.
H&E, high power
PD-L1, high power
Mostly extrinsic induction of PD-L1 as acquired adaptive immune evasion. IFNγ can upregulate PD-L1 on tumor cells as well as TILs. MAPK over-activation, loss of PTEN implicated among other pathways. 5-10% of tumors express PD-L1 constitutively
Pardoll et al.
Conclusions
This study documents PD-L1 expression in an expanded series of metastatic cutaneous squamous cell carcinoma.
PD-L1 is expressed to a higher degree in locally advanced and regionally metastatic cases compared with low risk cutaneous SCCs
Histologically, expression seen often in areas of robust immune response
Remarkably high levels of PD-L1 expression were observed in several locally advanced and metastatic cases
Limitations include lack of clinical correlation
Relevance of PD-L1 in advanced cSCC is still unclear
High PD-L1 expression
H&E, low power
PD-L1, low power
High Expression: Partial or complete cell membrane staining (≥ 1+) in ≥ 50% of viable tumor cells
Left: 2.3cm grade 4 SCC invasive to subcutaneous fat, 9mm depth. High PD-L1 expression is visible in approximately 90% of viable tumor cells.
Brisk TILs are evident at the border of the tumor. Complete strong staining for PD-L1 is seen on tumor cell membranes.
Methods
Acknowledgements
We have previously described expression of programmed cell death ligand 1 (PD-L1) in 40 primary and 5 regionally advanced or metastatic cutaneous squamous cell carcinomas, and documented correlation of PD-L1 with histologic features which increase risk for metastasis [cite]. We here report a follow up to our previous study with the investigation of ten additional metastatic cases of cutaneous squamous cell carcinoma. Cases were collated from the files of [ ].  Immunohistochemical staining with anti PD-L1 antibody was performed at the Knoxville Dermatopathology Laboratory as previously described. Cases were reviewed by all four authors, and PD-L1 expression was categorized by the DAKO tumor proportion score method as negative, low, or high, as illustrated in the following panel.
H&E, high power
PD-L1, high power
Thank you to Paul Googe, MD, for mentorship on this project, and to Susan Foreman and Ada Brannan-Ramsey of Knoxville Dermatopathology lab for expert immunostaining
References
Slater NA, Googe PB. PD-L1 expression in cutaneous squamous cell carcinoma correlates with risk of metastasis. J Cutan Pathol. May 2016 (see for complete list of references)
Gianchecchi E, Delfino DV, Fierabracci A. Recent insights into the role of the PD-1/PD-L1 pathway in immunological tolerance and autoimmunity. Autoimmun Rev. 2013;12(11):
Pardoll DM. The blockade of immune checkpoints in cancer immunotherapy. Nat Rev Cancer. 2012;12(4):