A 46-year-old woman with known mixed connective tissue disease with clinical features of scleroderma and polymyositis and who was not on specific medications was referred to our institution to assess for interstitial lung disease due to her predisposing condition. She was a nonsmoker, had no respiratory symptoms, and enjoyed good exercise tolerance. She did not have any cutaneous lesions or renal disease. There was no family history of pulmonary or systemic disease. Her routine blood test results revealed a white blood cell count of 4.6 3 109/L (normal range, [4.4–10.1] 3 109/L), a hemoglobin level of 7.76 mmol/L (normal range, 7.26–9.18 mmol/L), a platelet count of 189 3 109/L (normal range, [170–380] 3 109/L), a bilirubin level of 8 mmol/L (7–19 mmol/L), and a creatinine level of 63 mmol/L (45–82 mmol/L), all within normal limits. Lung function tests at presentation yielded normal results, with a diffusing capacity for carbon monoxide of 95% and a forced vital capacity of 2.29 (98% predicted value). However, this patient had an elevated serum globulin level of 47 g/L (normal range, 26–32 g/L) and an erythrocyte sedimentation rate of 36 mm/h (normal range, 0–20 mm/h), while C-reactive protein level was normal at less than 0.35 mg/dL. She was seropositive for antinuclear (titer .1/720), anti-Ro, anti-La, and anti-extractable nuclear antigen antibodies. Chest radiography and CT were performed at presentation (Figs 1, 2) and 14-year follow-up (Figs 3, 4). PET/CT was performed at 7- (Fig 5, A and B) and 13-year follow-up (Fig 5, C and D). Throughout this 14-year follow-up period, she remained completely free of respiratory symptoms and continued to go for a brisk walk every day. At 14-year follow-up, there was no substantial change in serum laboratory values, but a lung function test revealed her diffusing capacity for carbon monoxide had decreased to 52%, while her forced vital capacity remained good at 95%; these findings were suggestive of interval development of restrictive lung function.On the chest radiograph at the time of referral to our institution, there was an area of focal lucency in the mediobasal left lower lung (Fig 1). Lung volumes were preserved, and there were no reticular opacities to suggest substantial fibrotic or interstitial changes. Chest CT at the time showed multiple thin-walled cystic lesions of variable sizes surrounded by normal lung parenchyma with associated small subcentimeter intra- and pericystic nodules, distributed in bilateral middle to lower zones without involvement of the apices (Fig 2). Most of the lung nodules were not calcified. The basal lucency identified on plain radiographs likely corresponded to the largest (4.3-cm) thin-walled cyst in the mediobasal left lower lobe (Fig 2e). During serial follow-up CT over a 14-year-period, there was a progressive increase in the number and size of the multiple lung cysts and pericystic lung nodules, with an interval increase in calcification of the lung nodules and cyst wall, as noted on the chest CT image obtained 14 years after initial presentation (Figs 3, 4). The largest cyst in the basal left lower lobe had more than doubled in size and measured 9.7 cm. The latest chest radiograph (Fig 3) also showed a substantial increase in cystic interstitial lung disease with basal predominance. The lung apices remained spared. Despite their progressive increase in size, the lung nodules were not fluorodeoxyglucose avid on PET/CT images (Fig 5). The patient underwent video-assisted thoracoscopic surgery (VATS) biopsy and was found to have aggregates of atypical lymphoid proliferation in the lung, suggestive of low-grade B cell lymphoma with plasmacytic differentiation favoring mucosa-associated lymphoid tissue lymphoma (MALT oma), as well as amorphous eosinophilic aggregates that were positively stained with Congo Red and crystal violet, compatible with amyloid deposition (Fig 6). What is your diagnosis?