How Cancer is Diagnosed

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There is no single definitive diagnostic test for cancer. Many tests and examinations are used to establish the diagnosis, as there are many kinds of cancer.

The type of cancer, as well as the part(s) of the body it affects, will guide a doctor's decisions about tests to order, as well as influence their choice of treatment.

Taking a person's medical history, performing a physical exam, ordering blood and imaging tests, as well as biopsies, are all steps a doctor might take if they suspect someone has cancer.

methods of diagnosing cancer

Verywell / Brianna Gilmartin


Early detection significantly increases the likelihood of cancer being treated successfully.

One proactive step you can take is performing regular self-checks at home. Cancers that you can do self-checks for include:

  • Breast cancer. The breasts should be regularly examined for any changes in shape and texture.
  • Testicular cancer. Regular checks of the testicles can detect changes in shape, size, or texture.
  • Skin cancer: Changes on the surface of the skin (anywhere from the head to the toes) that could be skin cancer include new warts, moles, spots or lumps.

If you notice something concerning when doing a self-check, see your doctor. While changes in the breasts, testicles, and skin are often normal, your doctor can order the tests necessary to rule out cancer.

Labs and Tests

Your doctor can choose from an array of medical tests that can help them diagnose cancer. If you aren't sure why you having a test, ask your doctor to explain why they have ordered it, or why they've chosen one test or scan over another.

Blood Tests

Blood tests measure the levels of substances in your body, such as red blood cells, white blood cells, and markers of inflammation. While blood tests can help, they cannot definitively diagnosis cancer.

A complete blood count (CBC) and a blood chemistry profile are two of the most common blood tests, but your doctor may also order more specialized tests.

  • Complete blood count. This test measures the number of blood cells, including white blood cells, red blood cells, and platelets, circulating in your body. The test also measures hemoglobin and hematocrit levels. Hemoglobin is an oxygen-carrying protein found in your red blood cells and in your blood as a whole. Hematocrit is the ratio of the volume of red blood cells to the total volume of blood. A complete blood count is particularly useful for diagnosing and monitoring cancers that affect the blood, such as leukemia.
  • Blood chemistry profile. Sometimes called a chemistry panel or metabolic profile, this test measures levels of fats, electrolytes, enzymes, hormones, and proteins in the body. The levels of these substances help a doctor see how well organs are functioning. For example, liver function tests measure proteins like albumin, and enzymes like alanine transaminase (ALT) and aspartate transaminase (AST). The levels of these proteins and enzymes indicate how well your liver is working.
  • Cytogenetic analysis. This test looks at white blood cells to see if there are changes in the number or structure of the cells' chromosomes. Alternatively, bone marrow cells may also be examined.


Urinalysis examines the appearance and contents of your urine for signs that may indicate cancer. Examining urine can help diagnose kidney and urothelial cancers (which affect the bladder, ureters, urethra, and renal pelvis).


To confirm a cancer diagnosis, your doctor will surgically remove some tissue or cells from the tumor in your body and send the sample to a lab for testing. This is called a biopsy.

There are many types of biopsies. The one your doctor performs will depend on the type of cancer suspected and where the tumor is located.

  • Fine needle aspiration (FNA). A small, thin, and hollow needle is used to remove cells and a little fluid from a tumor. If the tumor is deep within the body, an ultrasound or CT scan will be used to guide the needle.
  • Core biopsy. The needle used for a core biopsy is slightly larger than for FNA, but the procedure is similar. It's performed with local anesthesia to help reduce pain.
  • Excisional biopsy. A surgical procedure where the skin is cut and the entire tumor is taken out. The area is numbed with local or regional anesthesia. If the tumor is deeper in the body (such as in the stomach or chest) general anesthesia is used. Sometimes, the doctor may also remove some of the normal tissue surrounding the tumor.
  • Incisional biopsy. A surgical procedure similar to an excisional biopsy, except that only a small part of the tumor is removed (rather than taking it all out).
  • Endoscopic biopsy. A flexible, slim tube with a camera and light attached to one end (endoscope) is inserted into a specific part of the body, such as the mouth, nose, throat, bladder, and lungs. During the procedure, medical tools can be passed down through the tube to allow the doctor to remove cells or samples of tissue.
  • Laparoscopic biopsy. Similar to the endoscopic biopsy, this biopsy uses an instrument called a laparoscope to see inside the abdomen and obtain tissue samples.
  • Skin biopsy. Your doctor can select from different skin biopsies depending on the type of skin cancer they suspect. A punch biopsy removes a sample of the deep layers of the skin (epidermis, dermis, and subcutaneous fat). A shave biopsy removes the uppermost layers of the skin (the epidermis and part of the dermis). This test is suitable for diagnosing some types of basal cell or squamous cell skin cancers. Incisional skin biopsies remove parts of the skin down to the fatty layer. Excisional biopsies remove the entire tumor. Skin biopsies are performed using local anesthesia to numb the area.

Cytology Tests

Cytology tests look for cancerous cells in bodily fluids. Examples of body fluids cytology tests can be carried out on include:

Cytology tests can also be performed on cells scraped or brushed from a particular organ. This is called scrape or brush cytology.

A well-known example of this technique is a Pap smear, which looks for abnormal cells in cervical tissue. The mouth, esophagus, bronchi, and stomach can also be scraped and brushed for cells.

Other Tests

After you've been diagnosed, your doctor may order tumor marker tests and genetic tests to determine the exact type of cancer you have, assess its stage, and decide on treatment.

Anxiety and Cancer Testing

If you need tests to find out if you have cancer, it's normal to be anxious and upset. Look to your loved ones for support and know that even if the test confirms the diagnosis, many cancers can be treated (especially if they're found early).


Imaging tests let a doctor obtain images of the internal parts and organs of your body. These pictures help them see if there are tumors or changes that could be caused by cancer.


X-rays are fast, painless tests that use low doses of radiation to obtain images of different parts of your body. In some cases, a special contrast dye is given to make the pictures show up clearer. The dye may be given to you to swallow, injected into your veins, or passed to your intestine through your rectum.

Different X-rays are used to diagnose different cancers. For example, an X-ray of the chest can help diagnose lung cancer, while skeletal X-rays can detect bone cancers.

Computed Tomography (CT) Scan

A computed tomography (CT) scan uses an X-ray machine connected to a computer to take several pictures of your body from different angles, then processes them into cross-sectional images.

Like with regular X-rays, a special contrast dye may be given to you to make the pictures clearer or help your doctor see a specific organ or structure better.


This scan involves the use of high-frequency sound waves to generate images known as sonograms. Ultrasounds can help diagnose cancers located in areas that don’t show up clearly on X-rays.

Ultrasounds can also help doctors guide needles during a fine-needle aspiration or core biopsies.

Magnetic Resonance Imaging (MRI) Scan

Like CT scans, a magnetic resonance imaging (MRI) scan creates cross-sectional images of your body. Instead of using X-rays, MRIs use magnetic fields and radio waves to create high-resolution pictures.

MRIs can also help determine whether cancer has spread (metastasized) to other parts of the body.


Breast cancer can be detected with a type of X-ray called mammograms. Mammography machines are specifically designed to examine breast tissue for abnormalities.

Before having a mammogram or any other type of X-ray, let your doctor know if there's any chance you could be pregnant. Depending on the area of your body that needs to be X-rayed, you may need to take special precautions to avoid or reduce fetal exposure to radiation.

Nuclear Medicine Scans 

These tests help doctors find tumors and correctly stage cancers. These tests use radionuclides (substances which you swallow, inhale, or are injected with) that give off small doses of radiation.

The radionuclide, also called a tracer, accumulates in your body. With the aid of special cameras and computers, your doctor can obtain 2D and 3D images of the part of the body being tested.

Nuclear scans don't hurt and can be done on an outpatient basis. Examples include bone scans, MUGA scans, thyroid scans, gallium scans, and PET scans.

Endoscopy Procedures

For endoscopic procedures, a doctor inserts a tube-like device into your body so they can see inside. The tube, called an endoscope, has a light and small camera attached to its end.

Endoscopy procedures used to diagnose cancer include:

Screening Tests

Screening tests help detect cancer before a person has any signs or symptoms.

There are reliable screening methods for many, but not all, types of cancer.

People at increased risk for certain cancers may need to be screened regularly. For people who don't have specific risk factors, routine screenings for specific cancers may be recommended once they reach a certain age.

According to CDC data, screening tests can help prevent deaths from certain types of cancer through early detection.

Breast Cancer

Breast cancer can be screened in the following ways.

  • Mammogram. A type of X-ray designed specifically for breasts. The scan can show tumors and detect irregularities.
  • Self-examination. Checking your own breasts at home for changes in shape or size.
  • Physical examination by a physician. Your doctor looks at and physically examines your breasts and nipples.
  • Breast MRI. A type of MRI designed specifically to detect breast tumors.

Colorectal Cancer

There are several tests and procedures used to screen for cancer of the colon and rectum, including:

  • Colonoscopy and sigmoidoscopy. A tube with a camera is inserted into the anus to allow a doctor to see inside the rectum and large intestine.
  • Stool DNA test. Analysis of your stool for DNA changes typical of colorectal polyps or cancer.
  • Double-contrast barium enema. An X-ray of the colon and rectum, in which barium enema is used as a contrast agent to make the colorectal area show up more clearly.
  • Fecal occult blood test (FOBT). Detects tiny traces of blood in the stool, which can be a sign of colorectal polyps or cancer.

Cervical Cancer

There are two main tests used to screen for cervical cancer.

  • Pap smear. The collection of cells from the cervix, through scraping, to check for abnormal cell changes.
  • HPV test. Similar to a Pap smear, but strains of human papillomavirus (HPV)—a sexually transmitted infection that strongly increases a woman’s risk of cervical cancer—are also checked for. Your doctor may only recommend an HPV test if your pap smear results are abnormal.

Prostate Cancer

According to the Centers for Disease Control and Prevention guidelines, most people with a prostate should start talking to their doctor about routine prostate cancer screenings by the age of 55.

  • Digital rectal examination. A doctor inserts a gloved finger into your rectum to examine your prostate for any abnormalities.
  • Prostate-specific antigen (PSA) test. A blood test that measures the level of the prostate-specific antigen in your body. Higher than normal levels may indicate prostate cancer.

People who are high-risk for prostate cancer may be advised to begin regular screenings at a younger age.

Skin Cancer

It's a good idea to get in the habit of checking your skin for changes, but the CDC doesn't recommend regular skin cancer screenings for people without specific risk factors.

However, if you've had skin cancer before or have a skin change (such as a new mole) that needs to be monitored, it's important to regularly check in with your doctor.

  • Physical examination. Your doctor will look at and touch your skin to look for signs of skin cancer.
  • Dermoscopy. With the aid of a medical instrument called a dermatoscopy, your doctor will look more closely at any pigmented skin lesions on your body. The exam is particularly useful for catching melanoma early.

Drawbacks of Screening Tests

There are risks and drawbacks of screening tests. Some cancers grow slowly and will not cause any symptoms or illness in your lifetime. In these cases, screenings can lead to "overdiagnosis" and medical care you don't need.

While screening tests can help diagnose cancer, they are not perfect. Sometimes, the tests do not detect cancer that is present. Other times, the results of the test indicate someone has cancer when they do not. False positives are a risk of any cancer screening.

Inaccurate cancer test results are extremely stressful and can also be a financial burden. For example, the cost of pursuing more diagnostic tests when they are not actually necessary.

If you regularly do self-checks at home and are concerned about cancer, talk to your doctor. They will be able to help you understand your risk, as well as the risks of the test used to diagnosis cancer. Together, you can decide which screening tests are right for you, and when you should begin having them.

Frequently Asked Questions

What are the typical first warning signs of cancer?

There are many general symptoms that indicate the possible presence of cancer, including (but not limited to):

  • Loss of appetite and/or unexplained weight loss
  • Blood in urine or in the stool
  • Constipation or diarrhea
  • Skin changes or sores or ulcers that do not heal
  • Unexplained fatigue
  • Persistent pain or headaches
  • Chronic cough
  • Fever and/or night sweats
  • Recurrent nausea or vomiting
  • Swollen lymph nodes

Can I diagnose cancer at home?

No. Only a doctor can definitively diagnose cancer and determine its stage (how advanced it is). However, there are home screening tests for colon cancer, such as Cologuard, for people who are at average risk of the disease. And there are self-exams you can do to check for signs of cancer, such as unusual moles or breast lumps.

How long can you have cancer and not know it?

That depends on the type of cancer. Some grow so slowly it can take years for them to be diagnosed, and some never cause any problems. An example of an extremely slow-growing cancer is carcinoid tumor, which can develop anywhere there are hormone-producing cells.Because certain cancers can exist for a long time before they cause symptoms, screening and regular health checks are vital.

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Article Sources
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Additional Reading
  • National Cancer Institute. How Cancer Is Diagnosed. U.S. Department of Health and Human Services, National Institutes of Health, National Cancer Institute. Updated July 2019.

  • National Cancer Institute. Understanding Laboratory Tests Fact Sheet. U.S. Department of Health and Human Services National Institutes of Health, National Cancer Institute. Updated December 2013.