What is the purpose of diagnostic tests?

Cancer patients undergo many different types of tests in order to accurately diagnose their disease, determine their prognosis, and monitor their cancer for progression or recurrence.

The term “diagnostic test” can be misleading, as these tests are not used only for diagnosing cancer, but also for monitoring cancer progression. There are many reasons for employing diagnostic tests depending on whether the disease is active or progressing, being treated, or in remission. Diagnostic tests may be used to:

• Diagnose primary disease—identify the disease the first time it occurs
  
• Identify cancer subtype—some cancers are divided into subtypes that are more or less aggressive; identification of a more aggressive subtype may influence the type of treatment proposed
  
• Predict prognosis—test results may indicate chance of cure, based on outcomes of other patients with similar results
  
• Direct treatment—cancer is many different diseases, all of which respond differently to various treatments. A diagnosis that accurately identifies the type of cancer and predicts prognosis will also help to identify the type of treatment that maximizes chance of cure.
  
• Evaluate response to treatment—some tests show whether the cancer is responding to treatment
  
• Detect minimal residual disease—cancer cells that remain after treatment is completed are called (MRD). Detection of MRD may indicate a higher likelihood of recurrence.
  
• Monitor remission or progression—if a cancer is in remission, frequent tests may help detect the cancer if it returns and/or determine whether it is progressing
  
• Screen at-risk individuals—identifying abnormalities in cells or the DNA of cells of asymptomatic (healthy) individuals may indicate an increased risk (although not a certainty) of developing disease
  

Pathology Tests: Pathology tests involve microscopic evaluation of abnormal cells.

Diagnostic Imaging: Diagnostic imaging involves visualization of abnormal masses using high-tech machines that create images. Examples of diagnostic imaging include x-rays, computed tomography (CT) scans, positron emission tomography (PET) scans, magnetic resonance imaging (MRI), and combined PET/CT scans.

Blood Tests: Blood tests measure substances in the blood that may indicate how advanced the cancer is or other problems related to the cancer.

Tumor Markers: Tumor marker tests detect substances in blood, urine, or other tissues that occur in higher than normal levels with certain cancers.

Genomics: Special laboratory evaluation of DNA involves the identification of the genetic make-up-the DNA-of the abnormal cells.