While there was no difference in <i>APOBEC3B</i> between wild-type versus mutated PIK3CA DCIS, <i>APOBEC3B</i> was higher in wild-type versus PIK3CA-mutated IBC.
PIK3CA mutation was independently associated with worse metastasis-free survival (MFS) in IBC since the median MFS for the PIK3CA mutant type was 26.0 months and for the PIK3CA wild type was 101.1 months (p = 0.002).
Molecular aberrations affecting the PI3K pathway may play a role in the progression from high-grade DCIS to IBC in a subset of cases (e.g., a subgroup of ER-positive/HER2-negative lesions).