The Conundrum of Diagnosing Cutaneous Composite Lymphoma in the Molecular Age

Introduction: Cutaneous composite lymphoma (CCL) is extremely rare. When 2 potentially distinct lymphoid lesions occur at one skin site, distinguishing between one neoplastic clone and a secondary reactionary lymphoid response versus a second neoplasm is difficult. In this study, we describe a unique case of CCL along with a review of reported cases in literature to identify clues and discuss issues that are relevant to the diagnosis of CCL. Design: Review of a CCL case from our institution and a systematic review of reported cases of CCL in the literature. Results: A total of 18 studies describing 22 cases and a case report from our institution are included. The mean age at diagnosis was 68 years. Most cases herein presented with multiple skin lesions (67%) and reported a history of immune suppression (76%). Nineteen cases (83%) had a combination of T-cell and B-cell neoplasms, whereas the remaining cases had 2 distinct B-cell clones. Clonal differentiation was confirmed based on morphology and immunohistochemistry in all cases, and by polymerise chain reaction studies in 19 cases. Complete remission was achieved in only one quarter of reported cases. Conclusion: Diagnosing CCL can be challenging because accurate differentiation of 2 or more clonal populations at 1 site is tedious. A stepwise approach and integration of clinical, morphologic, immunohistochemistry, and molecular data along with an understanding of the prognosis of the lymphomas in question is essential for an accurate diagnosis and necessary because of therapeutic and prognostic implications.