Symptoms of cancer

[Agnes]

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.