AbstractBackgroundCutaneous hypersensitivity eruptions in chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) are a clinically and histologically heterogeneous group that can either precede, occur with, or follow the development of a hematologic malignancy. Therefore, establishing the diagnosis requires careful clinical and pathologic correlation and an understanding of the broad spectrum of presentations. Data is lacking on the correlation of skin disease with molecular/cytogenetic risk profiling of the tumor.ObjectivesThe aims of this study were to characterize the clinical, histological, and genetic aberrations in recurrent cutaneous hypersensitivity reactions in patients with CLL/SLL.MethodsA single site academic retrospective chart review of medical records, histopathology, molecular and cytogenetic data in CLL/SLL patients who developed biopsy‐proven cutaneous hypersensitivity reactions.ResultsFive hundred one new diagnoses of CLL/SLL with 73 patients requiring cutaneous biopsies for skin lesions or rashes were identified. With exclusion criteria, 20 biopsies were identified from 17 patients (mean age, 69.6 years, females = 9) with unexplained cutaneous eruptions. These were commonly pruritic, erythematous papules above the waist. Most biopsies had a prominent superficial, deep dermal eosinophilic infiltrate (85%), with a robust T‐cell predominant dermal infiltrate in 40%. Five out of 17 patients (29%) had a predominately folliculocentric CD4+ T‐cell infiltrate; all occurring on the head and neck. Overall, the prevalence of cutaneous hypersensitivity eruptions requiring biopsy was 3.4% (n= 17), and the prevalence of folliculocentric CD4+ T‐cell infiltrate was 1% (n= 5).ConclusionCutaneous hypersensitivity reactions in CLL/SLL are heterogeneous; however, folliculotropic CD4+ T‐cell infiltrates may be seen in a small but distinct clinical subset of patients. Commonly tested cytogenetic aberrations in CLL/SLL do not appear to be correlated with the presence of cutaneous hypersensitivity reactions.