Radiation Recall Phenomenon Following Vaccination in a Patient With Prior Radiation to Lower Extremity Liposarcoma.

Radiation recall phenomenon (RRP) is a rare inflammatory reaction in previously irradiated tissue triggered by agents such as chemotherapy or vaccines. A 67-year-old female patient who had undergone radiation to the right thigh for liposarcoma developed a blister at the same site during whole breast radiation for invasive lobular carcinoma. This occurred three days after receiving COVID-19, respiratory syncytial virus (RSV), and influenza vaccines. The reaction progressed to an ulcer over two months, while her active breast radiation site remained unaffected. This case highlights vaccination as a potential RRP trigger and the selective involvement of prior radiation fields. Awareness of RRP in vaccinated patients with a history of radiation is essential, warranting further research into its mechanisms.