Final answer:
The first symptom of a Pancoast tumor in 90% of cases is shoulder pain that radiates to the arm, caused by the tumor's impact on surrounding nerves.
Step-by-step explanation:
The first symptom in 90% of Pancoast tumor cases is shoulder pain that radiates to the arm. This occurs due to the tumor's location at the top of the lung, which can affect nearby structures such as nerves leading to the arm. In addition to the typical shoulder pain, other signs and symptoms of a Pancoast tumor may include unusual lumps or swelling at the tumor site, persistent cough, hemoptysis (coughing up blood), pain and/or ulceration, enlarged lymph nodes, hepatomegaly (enlarged liver), bone pain, fractures of affected bones, neurological symptoms, weight loss, poor appetite, fatigue, cachexia (wasting), excessive sweating (like night sweats), anemia, and specific paraneoplastic phenomena, which are conditions caused by the presence of cancer in the body, such as thrombosis or hormonal changes.