C59-11 Cystic Pulmonary Metastasis as an Unusual Presentation of Colorectal Adenocarcinoma

Abstract Background Cystic lung lesions in young adults are most often evaluated for benign or inflammatory etiologies such as pulmonary Langerhans cell histiocytosis, lymphangioleiomyomatosis, congenital cystic disorders, or infection. Cystic pulmonary metastasis from colorectal cancer is exceedingly rare and may lead to diagnostic uncertainty and delay. Early recognition and biopsy are essential for timely oncologic management. Case Presentation A 38-year-old man with history of hypertension presented with abdominal pain, nausea and vomiting for one week. He denied cough, fever, chest pain, recent travel, immunosuppression, or chemical exposure. History is significant for incarceration, released 6 months ago. The patient reports active tobacco use for past 6 months since release. Physical exam was unremarkable. Contrast-enhanced CT of the chest revealed a lobulated thin-walled cystic mass in the left lower lobe lung measuring 6.3 x 4.9 cm with small satellite areas and right lower abdominal mass measuring 5.3 x 8.3 x 6.5 cm. Infectious workup including echinococcosis IgG, serum IgE, T-spot, and respiratory AFB cultures were all negative. Carcinoembryonic antigen (CEA) was markedly elevated at 381 ng/ml. Given diagnostic uncertainty, interventional radiology guided biopsy of the pulmonary lesion was performed and revealed metastatic adenocarcinoma of glandular forming epithelial cells positive for CDX2 and CK20 and negative for TTF-1 and CK 7, confirming colorectal origin. Subsequent Colonoscopy identified ascending colon mass. Biopsy confirmed a moderately differentiated adenocarcinoma consistent with the lung findings. Further staging workups showed no additional metastatic sites. Patient underwent systemic chemotherapy with a FOLFOX regimen) and remain under close surveillance. Discussion Cystic lung metastases from colorectal cancer are exceptionally rare. Proposed mechanisms include necrosis of micrometastases, airway check-valve obstruction, and cavitation after tumor embolization. These lesions can mimic benign cystic lung diseases radiographically, leading to potential diagnostic delays. Tissue biopsy is crucial when cystic pulmonary lesions are detected in patients with known or suspected malignancy, especially when imaging findings are inconclusive. This case highlights the importance of maintaining suspicion for metastatic disease even in atypical presentations, such as cystic lung lesions in young individuals. Conclusion Cystic pulmonary metastasis represents a rare manifestation of colorectal cancer and can occur in younger patients. Clinicians should include metastatic disease in the differential for cystic lung lesions, particularly when infectious workup is negative and imaging is non-diagnostic. Early biopsy and histopathologic confirmation are essential for accurate diagnosis and appropriate management. This abstract is funded by: none