PIK3CA and hidradenocarcinoma: Similarly we detected 2 types of mutations, c.1624G>A:p.Glu542Lys (in one hidradenocarcinoma and one porocarcinoma) and c.1633G>A:Glu545Lys (in one porocarcinoma), in exon 9 of PIK3CA. These 2 mutations are among the three most frequently reported mutations in breast cancer [43].