A 67-year-old man with
non-small-cell lung carcinoma was referred to our department because of a pruritic
rash on his head and upper extremities. Prior to the development of the
rash, he had received 4 cycles of combination
therapy with
pemetrexed,
carboplatin, and
pembrolizumab, followed by 2 cycles of
pembrolizumab monotherapy. On physical examination, violaceous scaly
erythema grouped on his scalp and upper extremities. Histologically, the scalp lesions demonstrated irregular acanthosis that formed a characteristic saw-tooth appearance with hypergranulosis and typical lichenoid tissue reaction. These findings suggested that the scalp lesions were
lichen planus. Two-week administration of topical
corticosteroid dramatically improved the
rash.
Immunotherapy with
pembrolizumab, an anti-PD-1 antibody, can induce T-cell activation that results in various immune-related adverse effects such as lichenoid tissue reaction. However,
lichen planus is generally found on the extremities and/or oral mucosa, and unlike in this case, the scalp is rarely affected. Although the exact mechanism underlying predominant scalp involvement is unknown, the present case indicates that anti-PD-1
therapy-induced
lichen planus can develop not only on the extremities and oral mucosa but also on the scalp. Interestingly, the lesions were not induced by the combination of
chemotherapy and
pembrolizumab; rather, they occurred soon after initiation of
pembrolizumab monotherapy. In the present case,
pembrolizumab-induced T-cell activation which triggered lichenoid tissue reaction may have been suppressed by
chemotherapy-induced immunosuppression. Dermatologists should have a thorough knowledge of the cutaneous lesions that manifest as irAEs of anti-PD-1
therapy.