My sister says she has pancoast syndrome. Are family members more likely to get the same thing?

No. Pancoast syndrome is caused by the pressure of a tumor high up in the top of the lung on the nerves (brachial plexus). This is usually from a lung cancer. Family members may not have the same risk factors that caused the lung cancer and if they do it may develop elsewhere and not in the same location. Most lung cancers are associated with smoking. If all family members smoke, they should stop.
No. Pancoast syndrome is generally caused by a malignant tumor in the superior sulcus of the lung, this causes involvement of the brachial plexus and stellate ganglion. The symptoms of pancoast syndrome are severe pain in the shoulder, wasting of the hand and arm muscles, horner syndrome and compression of blood vessels resulting in arm swelling. It is not familial.