PTEN and breast cancer: Norton et al. investigated copy number of 80 known cancer genes in all tumour foci from 11 patients with multifocal invasive lobular breast cancer and reported that copy number status was genetically homogenous across different foci in an individual patient.31 Recently, Desmedt et al. conducted targeted sequencing in different lesions from 36 multifocal breast cancers.14 Inter-lesional heterogeneity of oncogenic mutations such as PIK3CA, TP53, GATA3, and PTEN was present in 33% of the cases.