Radiation therapy in a ductal carcinoma in situ patient with ornithine transcarbamylase deficiency: a case report.

Ornithine transcarbamylase (OTC) deficiency is a rare urea cycle disorder that impairs ammonia detoxification, increasing the risk of hyperammonemic crises under metabolic stress. While chemotherapy-related risks have been reported, data on the safety of ionizing radiation therapy (RT) in this population are limited. This case describes a 30-year-old woman with late-onset OTC deficiency diagnosed with right-sided ductal carcinoma in situ. She underwent segmental mastectomy followed by adjuvant 3D conformal RT (40 Gy in 15 fractions with a concomitant boost to 48 Gy). Her multidisciplinary care involved preoperative hydration, close nutritional monitoring, and serial ammonia measurements. She completed RT without treatment interruptions or signs of hyperammonemia. This case illustrates that breast RT can be delivered safely in patients with OTC deficiency with a multidisciplinary, preventative approach. To our knowledge, this is the first report describing RT planning and metabolic surveillance in this population.