Klippel-Trenaunay syndrome belongs to the PIK3CA-related overgrowth spectrum (PROS).

Klippel-Trenaunay syndrome (KTS), originally described as a triad of cutaneous capillary malformation, bone and soft-tissue hypertrophy, as well as venous and lymphatic malformations, has been considered by dermatologists as a distinct diagnostic entity. However, cases with KTS have also been reported to have neurological disorders, developmental delay and digital abnormalities, indicating multisystem involvement. Recently, a number of overgrowth syndromes, with overlapping phenotypic features with KTS, have been identified; these include MCAP and CLOVES syndromes as well as fibroadipose hyperplasia. These conditions harbour mutations in the PIK3CA gene, and they have been included in the PIK3CA-related overgrowth spectrum (PROS). Based on recent demonstrations of PIK3CA mutations also in KTS, it appears that, rather than being a distinct diagnostic entity, KTS belongs to PROS. These observations have potential diagnostic and therapeutic implications for KTS.