Symptoms of Cancer - National Cancer Institute

If you have symptoms that last for a couple of weeks, it is important to see a doctor.

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Cancer can cause many symptoms, but these symptoms are most often caused by illness, injury, benign tumors, or other problems. If you have symptoms that do not get better after a few weeks, see your doctor so that problems can be diagnosed and treated as early as possible. Often, cancer does not cause pain, so do not wait to feel pain before seeing a doctor. 

from Cancer Information - Symptoms of Cancer - National Cancer Institute