Rosai-Dorfman disease mimicking testicular malignancy in a patient with marginal zone lymphoma of the lung.

Rosai-Dorfman-Destombes disease (RDD) is a rare, benign histiocytic disorder, most often involving lymph nodes but showing extranodal manifestations in nearly 50% of cases, particularly in the skin and upper respiratory tract. A hallmark histological feature is emperipolesis-large CD68+ and S100+ histiocytes containing intact inflammatory cells. We report a unique case of bilateral testicular RDD in a man with prior extranodal marginal zone lymphoma of the lungs. Three years after lymphoma remission, he presented with bilateral testicular enlargement. Ultrasound and positron emission tomography/CT showed diffuse hypoechoic parenchyma with metabolic activity suggestive of malignancy. Bilateral orchiectomy revealed tan-yellow, fleshy masses infiltrating the testicular parenchyma. Histology confirmed RDD with emperipolesis and S100+/CD68+/CD1a- phenotype. Testicular RDD is extremely uncommon, with only ~15 cases described to date, and its association with haematological malignancy remains poorly understood. Recognition of this entity is essential to avoid unnecessary oncological treatment.