If there is a cancelation of a doctor's appointment,the doctor does the cancelling and there is a diagnosis?

and there is a significant amount of time before the new appointment, and there is a diagnosis of something major,a debilitating illness or fatal illness, where the early diagnosis could have saved the patient, what are the legal ramifications, is there any legal recourse or avenues surviving relatives or friends of the deceased or disabled can avail themselves of, is the doctor liable in such a cancelation ?