Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha

PIK3CA Gene

• Full name: Phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha
• Location: Chromosome 3q26.32
• Function: Encodes the p110α catalytic subunit of class I phosphoinositide 3-kinase (PI3K), a key enzyme in the PI3K/AKT/mTOR signaling pathway.

Role in Cancer

• PIK3CA mutations are one of the most common oncogenic alterations in many cancers, including breast, colorectal, endometrial, and others.
• These mutations lead to constitutive activation of the PI3K pathway, resulting in increased cell growth, proliferation, survival, and resistance to apoptosis.
• In HR-positive, HER2-negative breast cancer, PIK3CA mutations occur in about 30-40% of cases.

Clinical Relevance

• Predictive biomarker:
  
  Detection of PIK3CA mutations guides targeted therapy decisions, especially for use of PI3K inhibitors such as Alpelisib.
• Testing:
  
  Typically performed via tumor tissue sequencing or circulating tumor DNA (liquid biopsy).
• Resistance:
  
  Mutations may contribute to endocrine therapy resistance in breast cancer.