Localized Lichen Planus Induced by Radiotherapy of the Breast; the “Isoradiotopic Response”

Radiation therapy (RT) is frequently associated with acute and chronic cutaneous adverse effects. Due to the proximity of breast tissue (as the target of radiation therapy) to the skin, breast cancer patients are at risk of these complications. Some of these adverse effects such as radiodermatitis are much more common and familiar to both the dermatologists and radiotherapists. Conversely, some of the other cutaneous reactions such as radiation-induced lichen planus (LP) as a kind of “isoradiotopic response” are less known, much rarer, and usually misdiagnosed. “Isoradiotopic response” refers to the development of a secondary, unrelated dermatosis in previously irradiated sites. For the first time, this term was used by Shurman et al., (2004) to describe a case of post- radiotherapy LP arising in the genital area two months after RT for penile carcinoma. The LP lesions were completely restricted to the field of RT.

We report the development of localized lichen planus in a 34-year-old female patient who received radiotherapy for invasive ductal carcinoma of the breast. She had no history of prior LP. Her LP lesions developed nine months after the termination of RT and were confined to the radiation field. Her LP lesions responded well to topical corticosteroids. However, after six months, her LP lesions recurred, involving the same area that showed a positive response to the treatment with topical corticosteroids. Over the next few years, she underwent some cosmetic and non-cosmetic surgical procedures, including delayed breast reconstruction with an implant, without Koebner phenomenon induction at surgical incision lines.

Although radiation-induced LP is a rare complication of RT, it is necessary for clinicians, especially dermatologists and radiotherapists, to be acquainted with it. As more patients with post-radiation LP are reported, investigators will be able to provide more information about the pathogenesis of the disease and evaluate the significance of different factors in its development.