Programmed cell death ligand-1 (PD-L1) expression in desmoid tumors: a retrospective study

Desmoid tumor is a rare benign but locally aggressive monoclonal and fibroblastic proliferation. It lacks metastatic potential but is associated with a high local recurrence after surgery. It is either characterized by the Beta-catenin gene (CTNNB1) or the adenomatous polyposis coli gene (APC) mutation. The most appropriate treatment approach is watchful waiting with periodic follow-ups for asymptomatic patients. However, symptomatic patients who are not good candidates for surgery due to high morbidity risk may benefit from medical therapy. The new drugs targeting programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) display promising results in many cancer types. This study assessed the PD-L1 status of desmoid tumors in 18 patients.

Biopsy and resection materials of 18 patients diagnosed with desmoid tumors between April 2016 and April 2021 were retrieved and assessed for PD-L1 expression. The prepared slides were immunohistochemically stained with PD-L1 antibody using Leica Bond® automated immunohistochemistry stainer.

No positive PD-L1 staining of the desmoid tumor cells was detected in any specimens. Intratumoral lymphocytes were present in all specimens. However, five of them were positively stained for PD-L1.

Based on the results of our study, anti-PD-1/PD-L1 therapy may not be a valuable option in desmoid tumor treatment due to the lack of expression of PD-L1 by desmoid tumor cells. Nevertheless, the presence of positively stained intratumoral lymphocytes may warrant further studies.