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Diagnosing Cancer

  • Lab tests, imaging studies, procedures and biopsies are used to diagnose cancer when suspected
  • For detecting cancer in any area of the body
  • The next step may be staging the cancer type and determining best treatment options
  • Involves Pathology and Radiology & Biomedical Imaging
Related Terms:

Diagnosing Cancer


Cancer is a broad term, referring to hundreds of different conditions that can develop in any part of the body. For this reason, symptoms range widely—from a tumor that you can see or feel, to one that affects how your body functions, to no symptoms at all. What’s the main thing all cancers have in common? They all begin when abnormal cells in the body start to grow and spread uncontrollably.

When doctors give a diagnosis of cancer, it’s never an assumption. They rule out other possible causes before they zero in on cancer. Then, working with other medical specialists, they carefully perform a series of tests to check (and double-check) the diagnosis.

“Cancer diagnosis and treatment is a multidisciplinary team effort,” says Yale Medicine pathologist Peter A. Humphrey, MD, PhD. “Our teams of doctors work together to detect the cancer, determine its aggressiveness and extent, and devise the best treatment and management plan.”

Our cancer experts are national/international leaders in their field, with the most up-to-date knowledge and skill in cancer diagnosis and treatment. “We have a large number of specialists with expertise in specific types of cancers, which is critical for the care of cancer patients,” Dr. Humphrey says.

How is cancer first detected?

The truth is that cancer can cause almost any symptom, depending on where the tumor is located, how big it is and whether it’s begun to spread. Some patients will be able to feel a lump (the tumor). This is mainly true for cancers that occur close to the body surface, like skin or breast cancer. 

But for cancers that grow internally, like stomach cancer, the tumor may go unnoticed for some time, allowing the cancer to advance. Meanwhile, general symptoms—weight loss, fever, fatigue—often develop.

Cancer is sometimes detected during a routine screening test (such as a mammogram or colonoscopy). Screenings are performed for common cancers, including colorectal, breast and prostate cancer. Guidelines (regularly reviewed and updated) indicate when people should be screened for cancer. Cancer can also be found incidentally, while the patient is being evaluated for another reason.

How is cancer diagnosed?

Once doctors suspect a patient might have cancer, they’ll ask about the family medical history and perform a physical exam. Then, they’ll run a series of diagnostic tests, including the following:

  • Lab tests - These check the levels of certain chemicals in the blood, urine and other body fluids—a level that’s too high or too low may be a sign of cancer.
  • Imaging tests - Images of internal organs may be examined for signs of cancer. Common imaging tests include MRI, CT scan, ultrasound, PET scan and X-ray.
  • Endoscopy - This procedure uses a specialized tool with a light or camera to look inside the body for a tumor.
  • Biopsy - A sample of the patient's tumor will be obtained and analyzed. This can be done during surgery or with a less invasive biopsy technique, in which the doctor inserts a needle into a targeted area, using an X-ray image as a guide. The biopsied (or resected) tissue is examined under the microscope by pathologists. These are the specialists who make the diagnosis of cancer, as well as determine the specific type of cancer and its aggressiveness, based on the tumor stage and grade. Pathologists use a number of methods to diagnose and characterize cancer cells, including, for example, molecular profiling to determine prognosis and the best therapy.  

What are cancer stages and grades?

Doctors use systems called staging and grading to measure how advanced the cancer has become.

Staging indicates the extent of the cancer in the body, particularly whether it has begun to spread. Several staging systems have been devised. One example is the “TNM” staging system, which considers three features of the cancer: the size of the main tumor (T), the number of affected lymph nodes (N) and the presence of metastasis (M). A number is assigned for each feature, with higher numbers meaning more severe disease. 

Grading is used to identify how different the tumor cells are from normal cells, based on the appearance of the cancer cells under the microscope. There are a number of different grading systems, and many cancers have their own. In general, a low number or grade indicates the potential for less aggressive behavior, whereas high numbers and high grade are often associated with potentially more aggressive cancers. 

These systems lead to a very precise understanding of the cancer, ultimately guiding decisions about treatment options. 

Why is Yale Medicine uniquely qualified to diagnose and treat cancer?

“Yale Medicine cancer experts in all fields provide the essentials for cancer care, starting with accurate diagnosis, typing, grading and staging of the cancer,” says Dr. Humphrey.

With the exceptional research environment at Yale, doctors use new diagnostic tools to perform cutting-edge medical research and write medical articles and textbooks that are used nationally as practice guidelines in cancer diagnosis and care. Yale Medicine doctors are true leaders in providing the best diagnosis and care for patients with cancer.