HISTOPATHOLOGY OF ALOPECIA IN THE SETTING OF CYCLIN-DEPENDENT KINASE 4/6 INHIBITOR THERAPY

Summary: Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are reported to contribute to alopecia in cancer patients; however, to our knowledge the histopathologic findings have not been described. Herein we describe the biopsy findings from a patient with alopecia following treatment with CDK4/6i, abemaciclib. The patient is a 42 year old woman with a history of breast cancer treated with neoadjuvant ddAC-T, lumpectomy and sentinel lymph node biopsy, and adjuvant radiation. She experienced hair loss during her neoadjuvant chemotherapy regimen with subsequent complete regrowth. Adjuvant letrozole and abemaciclib were initiated with patchy, persistent hair loss noted approximately 10 months later. Examination revealed marked decrease in hair density at the top and sides of scalp with apparent intact ostia. Punch biopsy of the scalp sectioned horizontally demonstrated 32 total hair follicles with a shift in the anagen to catagen/telogen ratio. Marked miniaturization was noted. There was a perifollicular lymphocytic infiltrate involving the lower segment along with peribulbar fibrosis; however, sebaceous glands were intact and features definitive for a scarring alopecia were not seen. We describe this case to contribute to the knowledge and understanding of alopecia in the setting of CDK4/6 inhibitor therapy.