The co-treatment of animals with AgNPs and BC resulted in decreased oestrogen receptor (ESR2) levels in the testes as compared to rats fed with a diet with BC alone, and the up-regulation of mRNA level of genes involved in T synthesis and metabolism (StAr, Cyp11a1, Hsd17b3, Hsd3b3, Cyp19a1, and Srd5a1), and steroid hormone signalling (AR, ESR1, and ESR2) compared to the Ctr group. This evidence concerns the gene CYP19A1 and breast cancer.