Case Report: First report of PIK3CA-related overgrowth spectrum revealed by refractory chylorrhea after breast-conserving surgery: failed thoracic-duct ligation.

Chylorrhea after breast-conserving surgery is exceedingly rare. We describe the case of a 38-year-old woman with refractory, isolated, cystic leakage from a breast cavity. All conventional interventions failed, whereas thoracic-duct ligation paradoxically increased chylous fluid drainage. Next-generation sequencing (NGS) of the extratumoral tissue revealed a somatic PIK3CA mutation, which led to a diagnosis of PIK3CA-Related Overgrowth Spectrum (PROS). To our knowledge, this is the first reported case linking PROS to chylorrhea after breast-conserving surgery, aggravated by duct ligation. Refractory surgical complications should be discussed and managed by a multidisciplinary team to identify or rule out occult diseases. These occult states that may be explained by somatic mosaic mutations are usually characterized by insidious or absent symptoms and are often diagnosed incidentally following surgical trauma or injury. In such contexts, precise genetic testing and targeted therapies may be pivotal and effective for diagnosis and treatment.