Hsa_circ_0055538 regulates tumor growth through the p53/Bcl2/caspase signaling pathway, demonstrated by an increase in TP53, BCL2-associated X, apoptosis regulator (BAX), apoptotic peptidase-activating factor 1 (APAF1), caspase 3 (CASP3), and CDKN1A expression, and a decrease in BCL2 expression in the hsa_circ_0055538 overexpressing cells. Here, APAF1 is linked to neoplasm.