Dear Doctor: Our sister saw her doctor because her chest felt "heavy," and he found fluid in her lung. Further tests showed lung cancer, which had already spread. She never coughed, and she quit smoking years ago. What are some of the symptoms of lung cancer?

Dear Reader: Although a cough can be an indication of lung cancer, it is not the only sign of the disease, and it doesn't appear in every case. Lung cancer can take years to develop; in its earlier stages, people may have no symptoms at all. When the disease does begin to make itself known, some of the symptoms can be unusual, and, thus, not immediately associated with lung cancer.

Let's start with a cough. It's one of the more common symptoms of lung cancer, and it appears in up to half of all patients. This can be a new and persistent cough that isn't associated with a cold or the flu, or it can be a chronic cough that gradually becomes worse. These coughs may be painful, and they may produce red or rust-colored phlegm or sputum, which indicates the presence of blood. Any time that you cough up blood — whether it is bright red, which indicates new blood, or a darker hue, which signals old blood — it's important to see a doctor.

The presence of fluid, as in the case of your sister, is known as pleural effusion. It's not actually inside the lungs, but in an area between the lungs and the chest wall, which is known as the pleural space. When it is associated with cancer, the condition is known as malignant pleural effusion, and it is a sign that the disease has spread. The buildup of fluid in the pleural space causes the sensation of heaviness that your sister reported, sometimes also described as a feeling of tightness. Often, it is accompanied by shortness of breath, a dry cough and exhaustion. Pleural effusion can be life-threatening, and the fluid must be drained.

Additional symptoms of lung cancer include chest pain, hoarseness, frequent bouts of bronchitis or pneumonia and persistent chest pain. Symptoms of the disease that are not lung-related include persistent fatigue or malaise, loss of appetite, unexplained weight loss, swollen or enlarged lymph nodes and shoulder or upper-back pain. Some patients develop an enlargement of the fingertips, known as clubbing. It's important to note that each of these, including cough, can be caused by other conditions.

For adults who are at a higher risk of developing lung cancer, the recent development of an early stage screening test has been an important advance. Known as low-dose computed tomography, or a low-dose CT scan, it's recommended for adults between the ages of 55 and 80 who are heavy smokers, or who were heavy smokers and quit less than 15 years ago. The scan, which uses a small amount of radiation, makes a detailed image of the lungs. Risks of the test include false positives, which can lead to unnecessary surgical procedures, and exposure to radiation, which itself can cause cancer. Anyone interested in the test should check with their doctor to see if they meet the screening criteria.

Eve Glazier, M.D., MBA, is an internist and associate professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and assistant professor of medicine at UCLA Health. Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.