T‐cell papulosis associated with B‐cell malignancy: a distinctive clinicopathologic entity.

Abstract: Background: A distinctive eruption referred to as ‘insect bite‐like reaction’ or ‘eosinophilic dermatosis of haematological malignancy’ has been described during the course of haematological B‐cell malignancies (BCM). However, its clinical evolution, histopathological features and pathogenesis remain unclear. Objectives: To characterize this eruption and to investigate its pathogenesis and relationship with the underlying BCM. Methods: In this multicenter retrospective study of the French Study Group on Cutaneous Lymphomas, 37 patients with a BCM and a cutaneous eruption consisting in chronic and/or recurrent papules, papulo‐vesicles and/or nodules were included. Clinical, histopathological, immunohistochemical and molecular data were reviewed. Results: No significant insect bite history or seasonal predominance was recorded. Patients had pruritic papules (81%), papulo‐vesicles (43%) and nodules (38%), often predominated in the head and neck region (84%), without complete remission periods in most cases (57%). The predominant associated BCM was chronic lymphocytic leukaemia (73%). Histological and immunohistochemical review showed a dense dermal lymphocytic infiltrate predominantly composed of T lymphocytes (100%), with frequent eosinophils (77.6%); a perivascular and periadnexal (most often folliculotropic) pattern (77.6%), sometimes suggestive of a folliculotropic mycosis fungoides; clusters of tumour B cells were identified in 47% of cases using appropriate phenotyping markers. In 10/14 cases (71.4%) tested for B‐cell IgH gene rearrangement, a B‐cell clone was identified in skin lesions (identical to the blood clone in nine cases), whereas no T‐cell clone was present. Conclusion: We propose the denomination ‘T‐cell papulosis associated with B‐cell malignancy’ (TCP‐BCM) for this distinctive eruption. Although resulting in various histopathological pictures, it can be easily recognized by clinicians and may be identified by informed pathologists relying on some key features. An extravasation of tumour B cells with skin‐homing properties associated with a secondary, predominant, T‐cell immune reaction could explain the clinicopathologic aspect and the prolonged regressive and recurrent course of the disease. [ABSTRACT FROM AUTHOR]