Even if you are uncomfortable discussing such personal problems, you should see your doctor if you think you have hemorrhoids. Your doctor may simply confirm your suspicions, or another diagnosis may be made. It could also be something else. If discomfort is accompanied by itching and you have recently returned from a trip abroad, for example, you might have parasites. You will need medical treatment to get rid of them.
Hemorrhoids can never become cancer, but hemorrhoids can bleed and cancer can bleed.
There could also be other conditions present requiring medical help. In most cases, the clot can be easily extracted by your doctor.