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. The gene discussed is ESR1; the disease is breast cancer.