Case Report: Unicentric Castleman disease mimicking metastatic lymphadenopathy in a patient with a history of triple-negative breast cancer and angiomatoid fibrous histiocytoma

Background Castleman disease (CD) is a rare and highly heterogeneous group of lymphoproliferative disorders. Its imaging manifestations may overlap with those of metastatic lymphadenopathy associated with malignant tumors, making the differential diagnosis of newly detected lymph node abnormalities particularly challenging in patients with a history of malignancy. Angiomatoid fibrous histiocytoma (AFH) is a rare intermediate soft tissue tumor, and the occurrence of CD in patients with a prior history of AFH has rarely been described. Case summary We report a 38-year-old Asian woman with prior left-sided triple-negative breast cancer treated with radical surgery and adjuvant therapy. Seven years later, a left post-occipital soft tissue mass was excised and diagnosed as AFH with an EWSR1 gene rearrangement. One year later, she noticed newly enlarged left cervical lymph nodes, raising concern for tumor recurrence or metastasis. Imaging revealed multiple lesions within the ipsilateral head and neck lymphatic drainage region. Excisional biopsy of a left level II cervical lymph node showed no evidence of malignancy on frozen section, while definitive histopathology established plasma cell-type Castleman disease. Subsequent 18 F-fluorodeoxyglucose positron emission tomography/computed tomography ( 18 F-FDG PET/CT) showed no definite abnormal lymphadenopathy in the thorax, abdomen, or pelvis, and biopsy of a left post-occipital lesion distinct from the excised AFH mass showed concordant CD-related changes. The disease was classified as unicentric Castleman disease (UCD) based on regional lesion distribution, laboratory and pathological findings, and the absence of overt systemic inflammatory manifestations or multiorgan involvement. Given the potential morbidity of complete excision, close surveillance was chosen. Six-month follow-up showed stable clinical and imaging findings. Conclusion This case highlights the diagnostic challenges associated with the rare sequential occurrence of triple-negative breast cancer, angiomatoid fibrous histiocytoma, and Castleman disease. In patients with complex oncological histories, newly detected lymphadenopathy should not be presumed to indicate tumor recurrence or metastasis, as tumor-associated lymphoid changes and Castleman disease may present with overlapping clinical and imaging features. Accurate diagnosis and classification require integration of histopathological findings, lesion distribution, laboratory results, and clinical context. Furthermore, management should be individualized according to disease distribution, surgical feasibility, potential morbidity, and the patient's overall clinical condition.