proc phreg data=bk;
    class white(ref='N');
    model dcgs_yrs*dcgs_censor(0)=age_at_tx white bk_viremia_tdc;
    if bk_viremia_yrs>dcgs_yrs or bk_viremia_yrs=. then do;
        bk_viremia_tdc=0;
    end;
    else do;
        bk_viremia_tdc=1;
    end;
run;

proc phreg data=bk;
    class white(ref='N');
    model dcgs_yrs*dcgs_censor(0)=age_at_tx white bk_viremia_tdc
    immuno_rx_tdc ivig_rx_tdc;
    if bk_viremia_yrs>dcgs_yrs or bk_viremia_yrs=. then do;
        bk_viremia_tdc=0; immuno_rx_tdc=0; ivig_rx_tdc=0;
    end;

    else do;
        bk_viremia_tdc=1; immuno_rx_tdc=immuno_rx; ivig_rx_tdc=ivig_rx;
    end;
run;

Parameter      Standard                                  Hazard
          Parameter           DF      Estimate         Error    Chi-Square    Pr > ChiSq       Ratio    Label

          AGE_AT_TX            1      -0.00415       0.01831        0.0515        0.8205       0.996    AGE_AT_TX
          white          Y     1       0.06509       0.53267        0.0149        0.9027       1.067    white Y
          bk_viremia_tdc       1      -0.69208       1.29703        0.2847        0.5936       0.501
          immuno_rx_tdc        1       0.33837       1.24702        0.0736        0.7861       1.403
          ivig_rx_tdc          1       1.05268       1.23367        0.7281        0.3935       2.865