At first, cancer, as a tiny mass of cells, causes no symptoms whatsoever (see also Overview of Cancer). As a cancer grows, its physical presence can affect nearby tissues (see also Warning Signs of Cancer). Also, some cancers secrete certain substances or trigger immune reactions that cause symptoms in other parts of the body that are not near to the cancer (paraneoplastic syndromes).
Sometimes the initial indication is an abnormal result on a laboratory test done for another reason (for example anemia resulting from colon cancer found on a routine complete blood count).
Cancer affects nearby tissues by growing into or pushing on them, thus irritating or compressing them. Irritation typically causes pain. Compression may keep tissues from performing their normal functions. For example, a bladder cancer or a cancerous lymph node in the abdomen may compress the tube (ureter) connecting a kidney with the bladder, blocking the flow of urine. A lung cancer may block airflow through one segment of a lung, causing partial lung collapse and predisposing to infection.
When cancer grows in an area with a lot of space, such as in the wall of the large intestine or the lung cavity, it may not cause any symptoms until it becomes quite large. In contrast, a cancer growing in a more restricted space, such as on a vocal cord, may cause symptoms (such as hoarseness) when it is relatively small. If a cancer spreads (metastasizes) to other parts of the body, the same local effects of irritation and compression eventually occur, but in the new location, so the symptoms may be quite different.
Cancers that involve the membrane covering the lungs (pleura) or the baglike structure that surrounds the heart (pericardium) often ooze fluid, which collects around those organs. Large fluid collections can interfere with breathing or the pumping of the heart.
Some Complications of Cancer
Many cancers are typically painless at first, although pain may be an early symptom of some cancers, such as brain tumors that cause headache and head and neck and esophageal cancers that cause painful swallowing. As cancers grow, the first symptom is often a mild discomfort, which may steadily worsen into increasingly severe pain as the cancer enlarges. The pain may result from the cancer compressing or eroding into nerves or other structures. However, not all cancers cause severe pain. Similarly, lack of pain does not guarantee that a cancer is not growing or spreading.
At first, a cancer may bleed slightly because its blood vessels are fragile. Later, as the cancer enlarges and invades surrounding tissues, it may grow into a nearby blood vessel, causing bleeding. The bleeding may be slight and undetectable or detectable only with testing. Such is often the case in early-stage colon cancer. Or, particularly with advanced cancer, the bleeding may be more significant, even massive and life threatening.
The site of the cancer determines the site of the bleeding. Cancer anywhere along the digestive tract can cause bleeding in the stool. Cancer anywhere along the urinary tract can cause bleeding in the urine. Other cancers can bleed into internal areas of the body. Bleeding into the lungs can cause the person to cough up blood.
Certain cancers produce substances that cause excess clot formation, mainly in the veins of the legs (deep vein thrombosis). Blood clots in leg veins sometime break off and travel to a lung (pulmonary embolism), which can be fatal. Excessive clotting is common in people with pancreatic, lung, and other solid tumors and in people with brain tumors.
Commonly, a person with cancer experiences weight loss and fatigue, which can worsen as the cancer progresses. Some people notice weight loss despite a good appetite. Others lose their appetite and may even become nauseated by food or have difficulty swallowing. They may become very thin. People with advanced cancer are often very tired. If anemia develops, these people may find that they feel tired or become short of breath with even slight activity.
As a cancer begins to spread around the body, it may first spread to nearby lymph nodes, which become swollen. The swollen lymph nodes are usually painless, and they may feel hard or rubbery. They may be freely moveable, or if the cancer is more advanced, they may become stuck to the surrounding tissues, or to each other.
Cancer can grow into or compress nerves or the spinal cord, causing any of several neurologic and muscular symptoms, including pain, weakness, or a change in sensation (such as tingling sensations). When a cancer grows in the brain, symptoms may be hard to pinpoint but can include confusion, dizziness, headaches, nausea, changes in vision, and seizures. Neurologic symptoms may also be part of a paraneoplastic syndrome.