Radiation recall dermatitis with abemaciclib developing a year after radiotherapy

Abstract Importance Cyclin-dependent kinases 4/6 (CDK4/6) inhibitors had been recently introduced in clinical practice approved for use in hormone receptor (HR) positive/ human epidermal growth factor receptor 2 (HER2) negative advanced or metastatic breast cancer. We report the first incidence of radiation recall reaction with the use of abemaciclib. Observations A 46-year old woman was diagnosed with oligometastatic HR+/HER2- breast cancer (L1 vertebra and right 8th rib). Following mastectomy and sentinel lymph node biopsy, she started letrozole with ovarian suppression. She received loco-regional radiotherapy (RT) to the chest wall and regional lymph nodes to a dose of 50 Gy in 25 fractions using a four-field technique. She was treated with stereotactic body radiotherapy (SBRT) to L1 and rib lesion to a dose of 28 Gy and 24 Gy in 2 fractions, respectively. She had developed grade 2 radiation dermatitis during RT. Subsequently, she was started on palbociclib, which was later switched to abemaciclib 100 mg twice daily due to neutropenia. Three months after switching (14 months after RT), she developed erythema and hyperpigmentation over areas of prior radiation dermatitis. The reaction was grade 2 radiation recall dermatitis (RRD) over the upper back and grade 1 reaction involving axilla, chest wall, and other sites receiving SBRT. The reactions stabilized over the next 3 months with some improvement with the use of emollients and topical steroids. Conclusion and Relevance This is the first incidence of RRD with the use of a CDK4/6 inhibitor upon switching to abemaciclib (receiving reduced dose) from palbociclib. The RRD possibly had a dose-dependent effect with grade 2 reactions developing over areas receiving higher skin dose.