Radiation-induced lichen planus as a kind of isoradiotopic response: a narrative review

Radiation therapy is frequently associated with a variety of adverse cutaneous effects. Some of these complications, such as radiodermatitis, are well known. However, some other skin reactions, such as radiation-induced lichen planus (LP) as a kind of isoradiotopic response, are rare, less known, and often underrecognized. An isoradiotopic response refers to the appearance of a secondary dermatosis in previously irradiated areas. In an isoradiotopic response, the new skin lesion presents with all the hallmarks of the primary dermatosis; however, the eruption is restricted to the field of radiation therapy. Radiation-induced LP as a kind of isoradiotopic response refers to the appearance of LP lesions in previously irradiated areas. This article presents a narrative review of the current literature about radiation-induced LP cases. The search was conducted on electronic databases, including PubMed, Web of Science, Cochrane, Scopus, Medline, Embase, and Google Scholar with the keywords, “isoradiotopic response,” “isotopic response,” “Koebner phenomenon,” “lichen planus,” “cancer treatment,” “radiotherapy,” and “radiation therapy.” According to the results of this search, there were only nine case reports of radiation-induced LP in the literature. Due to the limited number of articles published in this field, there are important questions, the answers of which are not known yet. By reporting more patients with post-radiation LP, investigators will be able to gather more information about the pathogenesis of the disease and evaluate the significance of different factors in the development of post-radiation LP.