CCNB1 and breast cancer: Furthermore, although circ-cyclin B1 (circ-CCNB1) could not directly bind to H2A histone family member X (H2AX) or p53 in breast cancer, circ-CCNB1, H2AX and p53 could form a ternary complex, which could be enhanced by circ-CCNB1 [37].