There are about 200 different cancers and each has its group of symptoms. Plus, each may "present" differently in different people. That's why your family doctor or even a specialist will consult or refer a patient to an Oncologist or a Hematologist.
Oncologists tend to specialize in tumors, Hematologists specialize in blood or bone marrow cancers [lymphomas, leukemias, etc.].
Cancers can be fast [acute] or slow [chronic] in their development. Also, some cancers can appear to stall in their development: they may grow at a regular pace, then stop and grow again. This can be either a symptom of that cancer, or for some totally unknown reason.
If you're worried that you may have cancer, ask for a referral to an Oncologist or Hematologist.
Visit the Cancer section of the National Institutes of Health for information: http://www.nci.nih.gov/