BI31 A case of unusual umbilical lichen planus associated with pembrolizumab

Abstract A 65-year-old White man developed violaceous, scaly, pruritic plaques on the umbilicus and lower back 12 weeks into adjuvant pembrolizumab therapy following nephrectomy for high-risk clear cell renal carcinoma. Initially thought to be psoriasis due to possible koebnerization on old scars, the rash expanded to involve the palms, thighs, buttocks, groin and penis. Diagnostic biopsies performed after dermatology review revealed hyperkeratosis, acanthosis with elongated rete ridges, vacuolar interface dermatitis, Civatte bodies and a bandlike lichenoid inflammatory infiltrate consistent with lichen planus. The rash resolved with oral and topical steroids and did not recur upon tapering, but pembrolizumab was discontinued. Skin reactions are among the most frequent immune-related adverse effects of checkpoint inhibitor immunotherapy across cancer types (Geisler AN, Phillips GS, Barrios DM et al. Immune checkpoint inhibitor-related dermatologic adverse events. J Am Acad Dermatol 2020; 83: 1255–68). Lichenoid reactions are one of the more common manifestations. However, checkpoint inhibitor-induced lichenoid reactions often present atypically, reflecting the diverse clinical patterns of immune dysregulation, and are thought to result from enhanced activity of T helper 1 and T helper 17 effector T cells. Lichen planus (LP) typically affects flexural and dorsal surfaces of the upper limbs, shins and lower back, with frequent oral mucosal involvement. Our case is notable for its atypical umbilical presentation. While Koebner phenomenon was considered, it was deemed unlikely as other scars remained unaffected. The programmed death-1 signalling pathway modulates cytokine production, including interferon-γ, interleukin-2, interleukin-17 and tumour necrosis factor-α. These are key mediators of immune dysregulation in LP and psoriasis, suggesting potential mechanistic overlap. Umbilical involvement in LP is exceedingly rare, with only three cases reported in the literature, including one instance of nivolumab-induced umbilical LP (Martos-Cabrera L, Lladó I, Fernández-Rico P, Butrón-Bris B, Rodríguez-Jiménez P. Umbilical lichen planus induced by nivolumab. An Bras Dermatol 2023; 98: 712–14). We describe a second case of checkpoint inhibitor-induced umbilical LP, adding to the limited but growing evidence of this uncommon manifestation. Checkpoint inhibitor therapy has revolutionized cancer treatment, but its immune-related side-effects require timely recognition and management to prevent severe outcomes. Increasing reports of atypical lichenoid reactions highlight the spectrum of these events. Our report adds evidence of umbilical and psoriasiform LP as a distinct clinical pattern, highlighting the importance of awareness among oncologists and dermatologists.