How difficult it is to understand whether a person has a cancer or not?

Diagnostic problems: I interpret your question to mean why is it difficult to tell if a person has or doesn't have a cancer? This is because many of the tests used are indirect tests such as cat scans and MRI scans. By using these radiology techniques, you get a picture that is suggestive of a cancer. There are characteristic features. The best test is an actual biopsy of the tissue. Sometimes, it is hard to do this.