Diagnosis can improve the effectiveness of treatments and avoid long-term complications for the infected patient. Undiagnosed patients can unknowingly carry the disease to others. Initial diagnosis can help to prevent or stop an outbreak. Widespread overuse and perversion of antibiotics contribute to antibiotic resistance. Diagnostic tests can ascertain when antibiotics are appropriate and when they are not.
Cancer can induce many different symptoms. Most often these signs are not caused by cancer, but by benign tumors or other problems. If you do find out you have cancer, your doctor will order another set of tests or procedures to figure out its stage. Stage relates to the extent of your cancer and is based on circumstances such as how large the tumor is and if it has spread.
Once the doctor knows the stage of your cancer, he will be able to recommend treatment and discuss your prognosis with you.
Usually, when a doctor first speculates cancer, some type of imaging studies, such as x-rays, ultrasonography, or computed tomography (CT), is done. For example, a person with chronic cough and weight loss might have a chest x-ray. A person with repeated headaches and trouble seeing might have brain CT or magnetic resonance imaging (MRI). Although these tests can show the presence, location, and size of an abnormal mass, they cannot confirm that cancer is the cause.
Cancer is authenticated by obtaining a piece of the tumour through needle biopsy or surgery and finding cancer cells on microscopic analysis of samples from the suspected area. Usually, the sample must be a piece of tissue, although sometimes examination of the blood is adequate (such as in leukaemia). Obtaining a tissue sample is termed a biopsy.
Biopsies can be done by cutting out a small piece of tissue with a scalpel, but very generally the sample is obtained using a hollow needle. Such tests are commonly done without the need for an overnight hospital stay (outpatient procedure). Doctors often use ultrasonography or CT to guide the needle to the right location. Because biopsies can be painful, the person is usually given a local anaesthetic to numb the area
When research findings or imaging test results suggest cancer, measuring blood levels of tumour markers (substances secreted into the bloodstream by certain tumours) may provide additional testimony for or against the diagnosis of cancer. In people who have been diagnosed with certain types of cancer, tumour markers may be useful to observe the effectiveness of treatment and to identify possible recurrence of cancer. For some cancers, the level of a tumour marker drops after treatment and raises if cancer recurs.
Some tumour markers cannot be measured in the blood but instead can be found on tumour cells. These markers are found by searching tissue from a biopsy sample. HER2 and EGFR are examples of tumour markers found on tumour cells.