Fibroadenoma is the most common benign breast tumor in women under 30 years. This study aimed to contribute to the knowledge of the genetic factors involved in the occurrence and progression of mammary fibroadenomas. MED12 and CYP17A1 were sequenced in fibroadenomas and blood in 43 Senegalese women. The Alamut-visual software, which includes the pathogenicity prediction software SIFT, Polyphen2 and MutationTaster, was used to search for mutations. DnaSP version 5.10.01, MEGA version 7.0.14 and Arlequin version 3.5.1.3 were used to determine phylogenetic parameters including indices of genetic variability and diversity and genetic differentiation parameters. A deletion in the poly-A tail of MED12 was identified in our study population. An alteration of Methionine (M1) was observed on exon 1 of CYP17A1. Our results also show that most of the variants found on exon 2 of MED12 and exon 1 of CYP17A1 have the probability of causing the appearance of breast fibroadenomas according by the three pathogenicity prediction software. We found 23 new variants on the MED12 gene and 109 new variants on the CYP17A1 gene. The amino acid frequency distribution between blood and fibroadenomas shows a statistically significant difference in Glycine, Arginine and Valine for MED12 and Cysteine, Phenylalanine, Histidine, Asparagine, Arginine, Tryptophan and Tyrosine for CYP17A1. In addition the selection test shows that codon 20 of exon 1 of CYP17A1 which codes for Arginine (p.20Arg) is under positive selection in mammary fibroadenomas. Genetic differentiation parameters show a clear difference between blood and breast fibroadenomas. These results show for the first time the involvement of the CYP17A1 gene in breast fibroadenomas and confirm the involvement of MED12. Codon 20 of exon 1 of CYP17A1 being under positive selection could be used as a biomarker in breast fibroadenomas.