CD40LG and familial atrioventricular septal defect: The typical immunophenotype of PCFCL is characterized by BCL6 expression and lack of BCL2, with IgM expression being rare (8% to 9%).2 Previous studies have suggested IgM as a marker to differentiate PCFCL from PCDLBCL-LT, where it is more commonly expressed (44% to 100%).2,29 The finding of IgM expression as a possible risk factor for ECD in PCFCL patients aligns with previous reports.