Hi and welcome to HCM.
Unfortunately you should trust doctors. During the surgery it can bee seen is cancer involving surrounding tissue or it is localized only in colon
. If chemo was advised then he obviously had this second situation and this is not curable anymore.
Chemo and radiotherapy are used when surgery cant hel but ih has serious side effects and many contraindications. One of them is WBC
decrease. ANd if this is notice,chemo must be canceled. You need to encourage and support your brother not to give up. Honestly, there is no specific treatment now. He can try to wait is his blood tests gonna recover and then consider chemoth again.
WIsh you good luck.