Study Assessing the Efficacy, Safety and PK of Alpelisib (BYL719) in Pediatric and Adult Patients With PIK3CA-related Overgrowth Spectrum

1. Signed informed consent and assent (when applicable) from the patient, parent, legal authorized representative or guardian prior to any study related screening procedures are performed
2. Patients with diagnosis of PROS with symptomatic and /or progressive overgrowth and at least one measurable PROS-related lesion confirmed by blinded independent review committee (BIRC) assessment
3. Documented evidence of a somatic mutation(s) in the PIK3CA gene performed in local laboratories

4. A tissue sample (fresh or archival) is be sent to a Novartis-designated central laboratory. If archival tissue is not available, collection of a fresh tissue biopsy is required for participants in Groups 1, 2 and 5, if it is not clinically contraindicated. For participants in Groups 3 and 4, a fresh tissue biopsy is not mandatory.

   For China only: Tissue sample collection and biomarker assessments are not applicable.

   For Germany only: If archival tissue is available, it must be sent to a Novartis designated central laboratory. If no archival tissue is available, obtaining a fresh tissue biopsy is recommended, if it is not clinically contraindicated, but is not mandatory.

5. Karnofsky (in patients > 16 years old at study entry)/Lansky (≤16 yrs of age at study entry) performance status index ≥50
6. Adequate bone marrow and organ function including Fasting plasma glucose (FPG) ≤ 140 mg/dL (7.7 mmol/L) and Glycosylated hemoglobin (HbA1c) ≤ 6.5% (both criteria have to be met) (as assessed by central laboratory for eligibility)
7. Presence of at least one PROS-related measurable lesion defined as a lesion with longest diameter ≥2 cm, when the volume can be accurately and reproducibly measured by MRI (Magnetic resonance imaging), and associated with complaints, clinical symptoms or functional limitations affecting the patient's everyday life. Measurability must be confirmed by BIRC before randomization.

1. Participant with only isolated macrodactyly, skin nevus/nevi and macroencephaly (the only clinical feature or a combination of any of three of them), in absence of other PROS-related lesions at the time of informed consent
2. Previous treatment with alpelisib and/or any other PI3K inhibitor(s) (except treatment attempt, defined as the attempt to treat PROS with any of PI3K inhibitors, with treatment duration less than 2 weeks and stopped at least 4 weeks prior to the first dose of study medication with alpelisib)
3. Radiation exposure for PROS treatment purpose within the previous 12 months on those PROS areas which are expected to qualify for target lesions (except lesion(s) progressing after completion of radiotherapy) at time of informed consent.
4. Debulking or other major surgery performed within 3 months at time of informed consent
5. Clinically meaningful PROS-related thrombotic event (Grade 2 and more as per CTCAE v.4.03) within 30 days before informed consent, and/or sclerotherapy/embolization for vascular complications performed within 6 weeks before informed consent. Note: Participants receiving anticoagulants for PROS-related coagulopathy, primary or secondary prophylaxis of thrombosis may be included in the study
6. Participants in Groups 1, 2 ad 5 with documented pneumonitis or interstitial lung disease at time of informed consent and with impaired lung function (e.g., FEV1 or DLCO ≤ 70% of predicted) that is not related to PROS. Participants in Groups 3 and 4 with documented or suspicious pneumonitis or interstitial lung disease based on MRI images at time of informed consent
7. History of acute pancreatitis within 1 year before informed consent or past medical history of chronic pancreatitis at time of informed consent
8. Participants with an established diagnosis of type I diabetes mellitus or uncontrolled type II diabetes mellitus at time of informed consent
9. Known history of seizure, or epilepsy, regardless of relatedness to PROS spectrum at time of informed consent, when epilepsy is not controlled and/or the patient may not be switched to non-enzyme inducing antiepileptic drug(s) at time of informed consent.
10. Participants with clinically significant worsening of PROS-related laboratory anomalies, physical signs and symptoms (such as, but not limited to increase of D-dimers, worsening of underlying pain, newly occurring swelling or redness) indicating an uncontrolled condition during the screening phase, particularly if systemic treatment with any other inhibitor of the PI3K/AKT/mTOR pathway was stopped prior to the start of study treatment. This includes but is not limited to hypercoagulability state in participants not receiving prophylactic treatment.

Other inclusion/exclusion criteria may apply