Abstract A035: A complex clinical evolution: Mediastinal unicentric Castleman disease preceding paraneoplastic pemphigus and bronchiolitis obliterans

Abstract Castleman disease (CD) is a rare condition characterized by lymph node hyperplasia and immune dysregulation, often presenting as a spectrum of disorders rather than a single entity. Although not a malignancy in the traditional sense, CD exhibits overlapping neoplastic features, creating diagnostic and therapeutic challenges. It is classified as either a localized (unicentric) or diffuse (multicentric) process, with unicentric CD (UCD) presenting at a younger age. We present a UCD case complicated by paraneoplastic pemphigus (PNP) and bronchiolitis obliterans (BO), demonstrating the diagnostic complexity and importance of prompt recognition and treatment. An asymptomatic 38-year-old woman was referred for evaluation of a 7.2-cm middle mediastinal mass adjacent to the trachea initially noticed abroad. The patient underwent CT-guided core needle biopsy which demonstrated reactive lymphoid tissue and an expanded paracortex, and was initially monitored without intervention. Within two months, she developed an intermittent dry cough with shortness of breath (SOB), for which empiric antibiotics and low-dose steroids were prescribed for presumed respiratory infection, although to no resolution. The patient was evaluated by pulmonology, in which pulmonary function testing revealed a fixed obstructive pattern. Concurrently, painful oral ulcers were evaluated by oral surgery, and buccal biopsy specimen showed microscopic and direct immunofluorescence findings concerning for PNP. Subsequent dermatologic evaluation included a PNP antibody panel which confirmed desmoglein-3 and envoplakin antibodies. Given worsening SOB and dyspnea at rest, the patient presented to the emergency department, and CT chest demonstrated tapering of multiple distal bronchi with hyperlucency of the lungs, consistent with BO. She was admitted and started on high-dose steroids (methylprednisolone 1g/day ×3 days), in addition to intravenous immunoglobulin (IVIG) (2 g/kg total), endorsed by rheumatology. As the mass was considered the primary driver of the paraneoplastic process, cardiothoracic surgery successfully resected the now-enlarged 9.1-cm mediastinal lesion; pathology confirmed hyaline-vascular CD. The patient experienced an uncomplicated postoperative recovery. After five days of observation, the patient denied SOB, weakness or fatigue, and was saturating comfortably on room air. A total of four cycles of IVIG were completed, and a long-term steroid taper was issued, along with appropriate Pneumocystis jirovecii pneumonia and gastrointestinal prophylaxis. This case underscores the importance of early recognition and treatment of CD. Despite its rarity, the tendency of the disease to affect younger patients emphasizes the need for a high index of suspicion when evaluating nonspecific systemic manifestations. The presence of a single mass can mimic multiple other etiologies, complicating the clinical picture and potentially delaying diagnosis. A comprehensive assessment coupled with multidisciplinary collaboration may ultimately enhance the likelihood of a favorable outcome. Citation Format: Chase V. West, Humberto R. Nieves-Jiménez, Matthew Washko, Ahmed Alderazi, Mohannad Safadi, Saadia A. Faiz. A complex clinical evolution: Mediastinal unicentric Castleman disease preceding paraneoplastic pemphigus and bronchiolitis obliterans [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: The Rise in Early-Onset Cancers—Knowledge Gaps and Research Opportunities; 2025 Dec 10-13; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(23_Suppl):Abstract nr A035.

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