Make an appointment with the oncologist and talk about what's bothering you. The doctor will examine you, prescribe a number of tests, as well as other studies, for example, ultrasound, mammography, computed tomography and other treatments - it all depends on the location of the tumor. At an early stage to identify cancer will help the usual analysis for tumor markers.
Then the specialist will decide on the feasibility of a biopsy - removal of a small piece of the tumor for histological examination. This is probably the most accurate way to determine what cells is the tumor. Don't be afraid collection procedure is performed under local anesthesia, so you will not feel pain.
After that, you will certainly recognize whether you have cancer. But in the very early stages when the tumor is quite small and the cancer poisoning the body decay products, perhaps the decision about analysis. If you are never going to bother with this problem, get tested after a short period of time again.
Pay close attention to their health, and at the first suspicious symptoms, contact your oncologist. Cancer is manifested by intoxication, pain in a specific area of the body, perceptible to the pressure-sensitive tumors, discoloration of the skin, General malaise and rise of temperature. But all of these symptoms can be somewhat different, it all depends on the affected organ.
Pass regular preventive inspection 1 time per year up to age 40, then 2 times a year, of course, if you do not bother. The only way to detect cancer early when it is still treatable.