PIK3CA and squamous cell carcinoma: A predominance of helical domain PIK3CA mutations was observed in patients with cervical squamous (100% vs. 0%), colorectal (67% vs. 33%), and squamous cell cancer of head and neck (60% vs. 40%), while PIK3CA kinase domain mutations were predominant in patients with uterine (86% vs. 14%), breast (83% vs. 17%), and ovarian cancer (71% vs. 29%; p = 0.002).