[When Is a Sick Person Obligated to Seek Treatment?]

Answer:
 If the sick person knows—by common experience, or because a physician has informed him—that his illness ordinarily leads to death, and he also knows—by common experience or the physician’s word—that treatment for that illness ordinarily results in recovery, then seeking treatment is obligatory. The proof is the rationally established principle that warding off harm from oneself is obligatory.
 If the sick person knows—by common experience or the physician’s word—that treatment for that illness does not ordinarily help (as with some cancers and some heart diseases), then treatment is not obligatory.
 If the sick person knows that treatment will not benefit due to extreme old age, treatment is not obligatory; here the consideration is the patient’s own preponderant judgment.
 If the patient does not fear the illness—because it is known by custom that such an illness is not life-threatening, or because a physician has indicated as much—then treatment is not obligatory.
 The guardian of a minor is obligated to obtain treatment for him when needed; likewise, a husband is obligated to obtain treatment for his wife when she needs it.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1