BackgroundThe aim of this study was to analyzePIK3CAmutations in exons 9 and 20 in breast cancers (BCs) and their association with clinicopathological characteristics.MethodsMutational analysis ofPIK3CAexon 9 and 20 was performed by Sanger sequencing in 54 primary BCs of Tunisian women. The associations ofPIK3CAmutations with clinicopathological characteristics were analyzed.ResultsFifteen exon 9 and exon 20PIK3CAvariants were identified in 33/54 cases (61%).PIK3CAmutations including pathogenic (class 5/Tier I) or likely pathogenic (class 4/Tier II) occurred in 24/54 cases (44%): 17/24 cases (71%) in exon 9, 5/24 cases (21%) in exon 20 and 2/24 cases (8%) in both exons. Of these 24 cases, 18 (75%) carried at least one of the three hot spot mutations: E545K (in 8 cases), H1047R (in 4 cases), E542K (in 3 cases), E545K/E542K (in one case), E545K/H1047R (in one case) and P539R/H1047R (in one case). PathogenicPIK3CAmutations were associated with negative lymph node status (p = 0.027). Age distribution, histological SBR tumor grading, estrogen and progesterone receptors, human epidermal growth factor receptor 2, and molecular classification were not correlated withPIK3CAmutations (p > 0.05).ConclusionThe frequency of somaticPIK3CAmutations in BCs of Tunisian women is slightly higher than that of BCs of Caucasian women and more observed in exon 9 than in exon 20.PIK3CAmutated status is associated with negative lymph node status. These data need to be confirmed in larger series.