This study is testing a medicine called zovegalisib (RLY-2608) for people with a condition called PIK3CA Related Overgrowth Spectrum (PROS). PROS happens when a gene called PIK3CA has a change, causing too much growth in parts of the body. The study has three parts: the first part finds the right dose, the second part looks at different groups, and the third part tests the medicine against a placebo (a pill with no medicine).

Key points:

• The study involves multiple visits and may require a biopsy (a small tissue sample) from the affected area.
• Participants must have PROS or a similar condition and may need to prove a specific gene change in their body.
• If you have heart problems or allergies to the medicine, you may not be able to join.

Participants will be checked to see if they can join based on their health and past treatments. They should not have received certain treatments too close to the study start. The study aims to find a safe and effective way to help those with PROS. Always talk to your doctor before joining a study.