Because your raw data is not aligned in columns, you need to use "Modified List Input" with the : and & modifiers. Please read about the meaning of & and : in this case
https://documentation.sas.com/doc/en/pgmmvacdc/9.4/lestmtsref/n0lrz3gb7m9e4rn137op544ddg0v.htm#p1wk2...
Also, you need two consecutive blanks after the treatment_type, which indicates that SAS will allow one blank in treatment_type but when it comes to two consecutive blanks, it stops reading treatment_type and starts reading the next variable.
Data treatment_details;
input patient_id 1-5
treatment_type & :$20.
start_date :mmddyy10.
end_date :mmddyy10.
response & :$20.;
datalines;
00001 Chemotherapy 01/01/2023 03/31/2023 Partial Response
00002 Immunotherapy 02/15/2023 05/15/2023 Complete Response
00003 Targeted Therapy 03/01/2023 06/30/2023 Stable Disease
00004 Chemotherapy 04/10/2023 07/10/2023 Progressive Disease
00005 Immunotherapy 05/20/2023 08/20/2023 Partial Response
00006 Chemotherapy 06/01/2023 09/30/2023 Complete Response
00007 Targeted Therapy 07/15/2023 10/15/2023 Stable Disease
00008 Chemotherapy 08/10/2023 11/10/2023 Progressive Disease
00009 Immunotherapy 09/20/2023 12/20/2023 Partial Response
00010 Targeted Therapy 10/01/2023 01/31/2024 Complete Response
;
--
Paige Miller