Pleural effusions related to lung cancer are quite common, so it's time that I discussed this issue. First, a pleural effusion is fluid outside of the lung, and it tends to follow gravity and pool at the bottom (base) of the lung, primarily along the back. Here's how it appears on a chest x-ray, filling up the bottom of the left side of the chest. The right side, in contrast, is mostly black, which is the way lungs should appear on a chest-x-ray (but not in real life, we hope).

(click to enlarge)

However, pleural effusions can also be loculated, which means that they don't follow gravity but rather are contained in pockets that are formed from scar tissue, inflammation, etc. Here's a CT image showing a loculated effusion on the left side, not freely flowing in the chest to follow gravity:

A few starting points to make. Not all pleural effusions in the world are from cancer, and in fact, it's probably just under half, with the balance being from infections and inflammatory reactions. Among the approximately 45% of effusions that are from cancer, lung cancer and breast cancer account for about 60%, with lung cancer as the leading cause (a little more than 1/3 of all malignant, or cancer-related, pleural effusions). They are important because the presence of cancer in the pleural fluid indicates systemic/advanced disease (although in SCLC the presence of a malignant effusion on the same side as the primary cancer is sometimes considered limited, and sometimes extensive, with no clear consensus), and because people can have symptoms of shortness of breath, cough, and sometimes pain from a pleural effusion, and relieving those symptoms is an important goal in managing lung cancer.

Clarifying that a pleural effusion is malignant can be challenging. Sometimes, the effusion is the first place people look to obtain a diagnosis of lung cancer, but we know that even in patients who ultimately are confirmed to have a malignant pleural effusion (MPE), it can be hard to find cancer cells in the fluid. This is usually done initially with a thoracentesis, which is a procedure in which a person has a needle inserted between the ribs in the back, sometimes under ultrasound or CT guidance, in an area where there is fluid beneath the skin, and fluid is then removed.

A thoracentesis can be diagnostic, which means it is being done to determine the cause of the fluid, for which usually only a syringe of fluid is removed, or it can be a therapeutic thoracentesis, in which the procedure is being done in order to remove as much fluid as possible to relieve symptoms for a patient, with sometimes as much as two liters of effusion fluid being removed.

The likelihood of finding cancer cells in the fluid from an initial thoracentesis is only in the 50-60% range. You can increase the chance of finding cancer of finding cancer overall by doing a second thoracentesis (or "tap"), but the likelihood of being successful the second time around after an initial negative tap is lower, in the 35-45% range. So it is possible to make a diagnosis of an MPE most but certainly not all of the time after 1-2 thoracenteses.

In cases where another source of tissue is not readily accessible, or if it is important for staging purposes to determine whether the pleural space is involved, thoracoscopy, or video-assisted thoracoscopic surgery (VATS), can be performed. This involves using a sterile tube with a light source and camera at the end that can go into the chest cavity through a small incision and get a look at what is happening. A surgeon can also take biopsies of suspicious tissue through the thoracoscope, and if necessary, can cut scar tissue and perform other manipulations through it. A picture of studding of the pleural space with tumor is shown here (cover the screen and don't enlarge if you're squeamish -- this is a surgery picture!):

Thoracoscopy can get a diagnosis more than 95% all the time. And while VATS is only a small, relatively minor surgery as far as chest surgery goes, it can still have complications such as bleeding, infection, or pain, usually in <10% of cases, and there are rare deaths (<2%). The VATS procedure, but the way, is the same general approach that is sometimes used to perform a lobectomy by specially trained thoracic surgeons, and that's a topic I'll discuss separately in the near future.

Once you have a diagnosis, managing the fluid buildup is another major issue to tackle. For some responsive cancers, such as lymphomas and SCLC, systemic therapy (such as chemo) is often enough to also treat the effusion. Some breast cancers, and also some NSCLCs as well, may be responsive enough to systemic therapy to not require additional interventions. However, many MPEs continue to recur and have significant symptoms associated with them. I'll discuss the more common ways to drain and manage the fluid collections next.