Calculate relapse rate from the end of a therapy

[NewUsrStat]

Hi guys, 

suppose to have the following:

data have1;
  input ID :$20. Start_Therapy :date9. End_Therapy :date9. Relapse :$20. End_follow_up :$20.;
  format Start_Therapy End_Therapy End_follow_up yymmdd10.;
cards;
0001 01JAN2015 30APR2018 yes  21JAN2021
0002 01MAY2007 31MAY2019 no   20DEC2021
0003 01JUN2011 31DEC2018 yes  12JAN2020
0004 06FEB2018 08FEB2021 yes  12APR2022
0005 09FEB2000 31AUG2018 no   01SEP2020
0006 01SEP2012 31DEC2019 yes  03MAR2021
0007 01JAN2011 30SEP2019 yes  06JUL2021
0008 01OCT2019 31DEC2020 no   21JAN2021
;

I have to calculate the relapse rate and I have to also use a statistical test to get the significance but I have no idea on how to do it. 

Can anyone help me please? 

I know that I have to calculate the person-time from the End_Therapy to the End_follow_up but I don't know how to do it since I'm new in the field. 

[PaigeMiller]

You can use PROC FREQ — example: https://documentation.sas.com/doc/en/pgmsascdc/9.4_3.4/statug/statug_freq_examples04.htm