Mechanistically, circ_0042881 exerted cancer-promoting effects in BC through sponging miR-217 to antagonize its inhibitive effect on SOS1, a guanine nucleotide exchange protein, thus activating RAS protein and initiating downstream signaling cascades, including the PI3K/AKT pathway and MEK/ERK pathway [57]. The gene discussed is PIK3CB; the disease is breast cancer.