Desmoplastic melanoma is a rare subtype of melanoma characterized by dense fibrous stroma, resistance to chemotherapy and a lack of actionable driver mutations, and is highly associated with ultraviolet light-induced DNA damage.   Samples from sixty patients with advanced desmoplastic melanoma treated with antibodies against programmed cell death 1 (PD-1) or PD-1 ligand (PD-L1) were analyzed.

Objective tumour responses were observed in 42 of the 60 patients (70%; 95% confidence interval 57–81%), including 19 patients (32%) with a complete response.

Immunohistochemistry analysis from nineteen desmoplastic melanomas and thirteen non-desmoplastic melanomas revealed a higher percentage of PD-L1-positive cells in the tumour parenchyma in desmoplastic melanomas (P = 0.04); these cells were highly associated with increased CD8 density and PD-L1 expression in the tumour invasive margin. Therefore, patients with advanced desmoplastic melanoma derive substantial clinical benefit from PD-1 or PD-L1 immune checkpoint blockade therapy, even though desmoplastic melanoma is defined by its dense desmoplastic fibrous stroma.