A80-3-02 Nodular Pulmonary Amyloidosis Mimicking Lung Cancer

Abstract Introduction Amyloidosis is a heterogeneous disorder characterized by extracellular deposition of misfolded protein fibrils that disrupt normal organ function. Although pulmonary involvement occurs in up to onethird of cases, presentation as a pulmonary nodule is exceedingly rare. Describing such atypical manifestations is crucial for improving diagnostic accuracy and preventing misinterpretation as malignancy. Case A 70-year-old woman, former smoker, presented with hemoptysis of a dime-sized amount daily. She had a remote episode eight years earlier without recurrence until starting antiplatelet for peripheral artery disease. She also has a family history of lung cancer and a remote history of kidney cancer treated with partial resection. CT scan showed a noncalcified 1.1 x 0.3cm curvilinear nodular opacity within the left lung base. Multiple bronchoscopies revealed blood clots in the left lower lobe without endobronchial lesions. Bronchoalveolar lavage grew viridans Streptococci and Candida but was negative for malignancy. Follow-up CT scan demonstrated enlargement of an irregular nodule to 1.2 x 0.6cm on a background of emphysema (Figure, left panel), raising suspicion for malignancy despite absent FDG uptake on PET/CT. Given the persistence of radiologic abnormality and patient preference, she underwent robotic wedge resection of the left lower lobe lesion. Histopathologic examination revealed Congo red-positive nodular deposits of amorphous eosinophilic material (Figure, right panel) exhibiting apple-green birefringence under polarized light, a diagnostic feature of amyloidosis. No evidence of malignancy was noted. The specimen was submitted for mass spectrometry-based amyloid typing, confirming AL (lambda)-type amyloidosis. Postoperatively, the patient remained asymptomatic without recurrence of hemoptysis or new nodules on follow-up imaging. There was no overt evidence of a plasma cell dyscrasia or a lymphoproliferative disorder, but subsequent workup was planned to take place at a specialized cancer center. Discussion Nodular pulmonary amyloidosis is an uncommon localized form of amyloid deposition that can radiologically resemble malignancy or granulomatous disease. The majority are associated with AL-type amyloid derived from immunoglobulin light chains, often linked to underlying plasma cell dyscrasias or localized B-cell proliferation. Diagnosis relies on histopathologic confirmation with Congo red staining and birefringence under polarized light. Surgical resection is both diagnostic and curative in most isolated cases, with excellent prognosis and low recurrence risk. Our case emphasizes the importance of including pulmonary amyloidosis in the differential diagnosis of solitary lung nodules, particularly when imaging findings are indeterminate, and highlights the role of tissue biopsy in guiding appropriate management and avoiding unnecessary extensive surgical interventions. This abstract is funded by: none