Abstract Introduction Chylothorax, the accumulation of lymphatic fluid in the pleural space, leads to loss of chylomicrons, lymphocytes, proteins, electrolytes, and fat-soluble vitamins. While it is a recognized complication of thoracic radiation in malignancies such as Hodgkin lymphoma or lung cancer, it is exceedingly rare after breast cancer radiotherapy. We present a case of delayed, recurrent chylothorax following adjuvant whole-breast irradiation, highlighting that even non-mediastinal fields can injure the thoracic duct. Case Description A 62-year-old woman with thymectomy for thymoma two and a half months prior, left breast invasive ductal carcinoma status post-lumpectomy and adjuvant whole-breast irradiation, and myasthenia gravis presented with progressive dyspnea. Chest X-ray revealed a large left pleural effusion, confirmed on CT angiography with left lung atelectasis.Ultrasound-guided thoracentesis yielded 1,500 mL of cloudy fluid. Pleural studies showed triglycerides of 1,679 mg/dL, cholesterol 140 mg/dL, and negative Gram stain, confirming a chylous effusion. Cytology was negative for malignancy. Dietary modification was initiated, and repeat thoracenteses every three weeks provided symptomatic relief. The effusion gradually decreased after completion of radiation and hormonal therapy. Referral to a tertiary center for possible lymphangiography and thoracic duct embolization was made, but the effusion resolved spontaneously, avoiding invasive intervention. Discussion Chylothorax is an uncommon but serious condition that can lead to hypovolemia, malnutrition, and immunosuppression, requiring early recognition and multidisciplinary management. In breast cancer, radiation-induced chylothorax is exceptionally rare yet anatomically plausible. The most likely mechanism in this case involves inadvertent radiation exposure to the terminal thoracic duct. Although whole-breast irradiation primarily targets the anterior chest wall, scatter or superior field extension—particularly when internal mammary or supraclavicular nodes are included—may incidentally irradiate the duct near the left subclavian-internal jugular junction. Delayed radiation-induced fibrosis, obstruction, or rupture of the thoracic duct can lead to chyle accumulation within the pleural space. Given its rarity, clinicians should consider this diagnosis in left-sided breast cancer patients presenting with recurrent, non-inflammatory pleural effusions after radiotherapy. The timing of chylothorax two and a half months after thymectomy, in the context of prior radiotherapy, suggested radiation injury rather than postoperative complication. Persistent or high-output leaks warrant escalation to lymphangiography or surgical ligation after failed conservative therapy. Conclusion Radiation-induced chylothorax should be suspected in left-sided breast cancer patients with recurrent, non-malignant pleural effusions after radiotherapy. Awareness of this rare complication promotes timely diagnosis and stepwise management to prevent nutritional and immunologic compromise. This abstract is funded by: none
Christian et al. (Fri,) studied this question.