PIK3CA and cancer: In their prospective two cohort studies, coexistence of PIK3CA exon 9 and 20 mutations but not in either exon alone, was associated with significantly worse cancer-specific survival (log-rank p = 0.0008; multivariate HR = 3.51; 95% CI, 1.28–9.62] and OS (log-rank p = 0.0008; multivariate HR = 2.68; 95% CI, 1.24–5.77) [80] (Table 2).