Praise be to Allah.
If your brother who has cancer is in the advanced stages of the disease and three trustworthy specialist doctors agree that he will certainly die if the life-support is removed and that there is no point in treating him, there is no need to use life-support.
It says in Fataawa al-Lajnah al-Daa’imah (25/80), explaining the cases in which measures should not be taken to resuscitate the patient:
If the patient is dead upon arrival at the hospital, there is no need to resuscitate the patient.
If the patient's case is one in which resuscitation is not appropriate, according to the report of three trustworthy specialist doctors, there is also no need to resuscitate the patient.
If the patient’s sickness is chronic and untreatable and he is definitely going to die according to three trustworthy specialist doctors, there is also no need to use life-support.
If the patient is incapacitated or is vegetative state and has a chronic disease or late-stage cancer, or has chronic heart and lung disease, in which the heart and lungs have stopped frequently, and three trustworthy specialist doctors confirm that, there is no need to use life-support.
If a patient shows signs of brain damage that cannot be treated according to three specialist trustworthy doctors, there is also no need to use life-support, because there is no benefit in doing so.
If resuscitation of the heart and lungs will be to no avail and is not appropriate in a given case according to the opinion of three trustworthy specialist doctors, there is no need to use life-support and no attention should be paid to the opinion of the patient’s relatives with regard to putting him on or taking him off life-support, because that is not their specialty.
Standing Committee for Academic Research and Issuing Fatwas.
‘Abd al-‘Azeez ibn ‘Abd-Allah ibn Baaz… ‘Abd al-Razzaaq ‘Afeefi
And Allah knows best.