Radiation recall pneumonitis from immune checkpoint inhibitors after extra pulmonary radiation

Radiation recall is an unpredictable, poorly understood inflammatory reaction within the confines of previously irradiated tissue that occurs following exposure to a systemic agent. In this article, we will focus on a subcategory of radiation recall, called radiation recall pneumonitis (RRP), precipitated by immune checkpoint inhibitors (ICI). Historically, RRP can develop weeks to years after radiation treatment to the lung, most commonly after receiving certain chemotherapeutic agents, but more recently has been recognized in association with immunotherapy agents (ICIs). Up until now, RRP following exposure to ICIs has been described in patients who have received radiation to the lung itself. Here we present three cases of RRP in patients who received radiation to areas adjacent to the lung parenchyma, and developed pulmonary infiltrates in an area adjacent to the radiation field while on ICI therapy. Since ICI induced RRP is treatable and steroid sensitive, early recognition and treatment are important.