Primary cutaneous diffuse large B cell lymphoma relapsed solely as a huge lung tumor mimicking a primary pulmonary lymphoma.

Primary cutaneous large B cell lymphoma, leg type (PCLBCL-leg) has recently been identified and recognized as a specific entity. Patients with PCLBCL-leg have a higher relapse rate and a poorer prognosis than the other types of primary cutaneous B cell lymphomas, and disease relapse is confined to the skin in the majority of cases with rare exclusive extracutaneous progression. The late occurrence of lymphoma in patients with a prior history of lymphoma may represent a relapse/progression or a distinct tumor unrelated to the original one. The distinction is of important clinical and therapeutic implications. Here, we report the case of a 90-year-old lady with a history of PCLBCL-leg in complete remission after radiotherapy that developed a huge, solitary pulmonary lymphoma without lymphadenopathy 14 months later. The latter was initially considered as stage IE primary pulmonary lymphoma and was treated with combination chemotherapy resulting in complete remission. Retrospective pathologic review and B cell clonality study revealed that the pulmonary tumor was a diffuse large B cell lymphoma of the same clonal origin as the PCLBCL-leg. This case is unique in the exclusive pulmonary relapse and illustrates the importance of expert pathological review and molecular study in the management of lymphoma patients with unusual clinical features.