Let-7a, a member of its family, can significantly downregulate the target gene HMGA1 to affect growth 49; miR-142-3p and miR-26a can be used as tumour suppressors to inhibit the expression of oncogene HMGA1 50, 51; miR-661 induces apoptosis after downregulating HMGA1 52; and miR-486-5p leads to G2/M cell cycle arrest and profound cell death of breast cancer cells by downregulating HMGA1 53. The gene discussed is HMGA1; the disease is breast carcinoma.