PIK3CA and neoplasm: However, the difference in median progression-free survival – specifically between the two treatment arms – was only 4 weeks (12.0 weeks in the combination group vs. 8.1 weeks in the lapatinib monotherapy group), and the majority of patients did not achieve a dramatic improvement in tumor response rate or survival, suggesting that the combined blockade of HER2 signaling is active even without chemotherapy, but may not be sufficient to overcome downstream PI3K/AKT pathways responsible for resistance to trastuzumab.