Do I have a case for malpractice?

My husband, was misdiagnosed for months by his PCP. He was told he had sleep apnea and bronchitis when he had cancer. He had lost 70 lbs in about four months, he had chronic back ache, shortness of breath, profound fatigue, stomach upset, lower blood pressure, he had skin cancer the previous year and he was having difficulty focusing. Although he was losing weight his stomach was still bloated and his stomach. It got so bad, I went to the doctor with my husband to see if the doctor was even listening to my husband. He wasn’t. The doctor looked me in the eye and said my husband had sleep apnea and bronchitis and wrote another prescription for antibiotics. No blood tests were performed, although my husband repeatedly told his doctor month after month that the antibiotics were not working. We called again, when the ever stronger antibiotics were not working, the doctor said if we thought it was not bronchitis to go to the emergency room. My husband had this doctor for years.