Cancer is caused by an abnormal overgrowth of cells with more than 100 cancer subtypes depending on which cell grows. In many cancers, the cells clump together to form solid tumors, but in some the cells are dispersed around the blood stream (leukemia) or the lymphatic system (lymphoma).
Prognosis of cancer has improved greatly in modern times owing to treatment advances and early detection programs. However, although survival rates have improved, cancer still remains the 2nd top cause of death, second only to heart disese in the USA.
Misdiagnosis of cancer is naturally possible but not common if professional medical advice is sought, because physicians will usually perform comprehensive diagnostic testing if cancer is a possibility. Diagnostic tests have also improved in accuracy including newer tumor marker blood tests. Self-diagnosis of cancer is usually incorrect and quite common is for people to fear that they have cancer based on a symptom (e.g. weight loss, persistent cough, lumps, or frequent urination), only to find out they have other less severe conditions. On the other hand, sadly common is for people to have cancer but be unaware of it, because many types have a slow insidious onset without early symptoms. For this reason, regular screening for particular types of cancer is valuable in preventing severe cancer cases.