Abstract: PIK3CA-associated overgrowth spectrum （PROS） is a class of rare diseases associated with mutations in the PIK3CA gene， which is mainly characterized by vascular abnormalities and soft tissue overgrowth. Although the clinical application of specific targeted pathway inhibitors has made some progress in recent years， some patients still suffer from drug resistance or poor therapeutic effects. In this paper， a child of PROS with a giant deformity of the right upper limb was reported. The child was found to have multiple swellings on the neck， chest， back， and both upper limbs since birth， which increased in size year by year. Among them， the anterior chest and the right upper limb were particularly obvious. The right upper limb gradually thickened， and was accompanied by spinal deformity， right shoulder dislocation and thoracic deformity. The patient had received sirolimus oral treatment and several times of localized volume reduction treatment， but failed to achieve the desired therapeutic effect. Second-generation gene sequencing showed that the child had missense variants at the ERBB2 and PDGFRA loci. Because oral targeted drug therapy and localized volume reduction therapy could not lead to longterm improvement of the lesion， and the child had severe hypertrophic deformity of the right upper limb， resulting in complete loss of limb function， the child’s clinical problem was finally solved by amputation surgery. By summarizing this case， this paper further supplemented and improved the study of PROS-related gene mutations， providing a new reference for the diagnosis and treatment of this disease.

Key words: PIK3CA-associated overgrowth spectrum, &emsp, Severe limb hypertrophy deformity, &emsp, Surgical treatment, &emsp, PI3K-AKT-mTOR signaling pathway, &emsp, Somatic mutation