How Cancer is Diagnosed

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There is no single definitive test that can confirm a diagnosis of cancer. Many different types of diagnostic procedures are used to establish the diagnosis because there are many different kinds of cancer.

The type of cancer and the affected part(s) of the body will guide your healthcare provider's decisions about which tests to order for you.

If your healthcare provider is concerned that you could have cancer, they will take your medical history, perform a physical exam, and possibly order blood tests, imaging tests, and/or a biopsy. And some types of cancer, like breast cancer and colon cancer, are often detected by routine screening tests.

methods of diagnosing cancer

Verywell / Brianna Gilmartin

Self-Checks

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 may be detected with self-checks for include:

  • Breast cancer: You should regularly examine your breasts for any changes in shape and texture.
  • Testicular cancer: Regular checks of the testicles can pick up on changes in shape, size, or texture.
  • Skin cancer: Changes on the surface of your skin, such as new or changing moles, spots, or lumps, can be signs of cancer. These can appear anywhere from your head to your toes.

If you notice something concerning when doing a self-check, see your healthcare provider . While changes in the breasts, testicles, and skin often turn out to be normal, your healthcare provider can order the tests necessary to see if it's cancer.

Labs and Tests

Your healthcare provider will select your medical tests based on the location and type of cancer they are concerned about. If you aren't sure why you're having a test, ask your healthcare provider 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 (RBCs), white blood cells (WBCs), and markers of inflammation. While blood tests can help identify some signs of many types of cancer, they usually cannot definitively diagnose cancer.

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

  • CBC: This test measures the number of blood cells, including WBCs, RBCs, and platelets circulating in your body. The test also measures hemoglobin and hematocrit levels. Hemoglobin is an oxygen-carrying protein found in your RBCs. Hematocrit is the ratio of the volume of RBCs to the total volume of blood. A CBC 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 fats, electrolytes, enzymes, hormones, and proteins in the body. The levels of these substances may help your healthcare provider identify certain problems. For example, liver function tests measure proteins like albumin, and enzymes like alanine transaminase (ALT) and aspartate transaminase (AST)—these levels indicate how well your liver is working.
  • Cytogenetic analysis: This test looks at WBCs to see if there are changes in the number or structure of the cells' chromosomes. Alternatively, bone marrow cells may also be examined.

Urinalysis

Urinalysis examines the appearance and contents of your urine and may sometimes detect signs of certain types of cancer, including kidney and urothelial cancers (which affect the bladder, ureters, urethra, and renal pelvis).

Biopsy

To confirm a cancer diagnosis, your healthcare provider may 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 healthcare provider 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 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, and the procedure is similar. It's performed with local anesthesia to help reduce pain.
  • Excisional biopsy: During this surgical procedure, the skin is cut and the entire tumor is taken out. The area is numbed with local or regional anesthesia. If the tumor is deep in the body (such as in the stomach or chest) general anesthesia is used. Sometimes, the healthcare provider may also remove some of the normal tissue surrounding the tumor to increase the chances of removing the whole tumor.
  • Incisional biopsy: This surgical procedure is similar to an excisional biopsy, except that only a small part of the tumor is removed.
  • Endoscopic biopsy: An endoscope (a flexible, slim tube with a camera and light attached to one end) is inserted into the body, through the mouth, nose, throat, bladder, or lungs. During the procedure, medical tools can be passed down through the tube so your healthcare provider can remove cells or samples of tissue.
  • Laparoscopic biopsy: Your healthcare provider will make a small incision and insert a laparoscope (a small surgical device with a camera) to see inside the abdomen and obtain tissue samples.
  • Skin biopsy: There are several types of skin biopsies, and they are done with local anesthesia to numb the area. A punch biopsy is done with a special device that removes a small sample, including several layers of 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 are done with a surgical incision to remove several layers of skin. Excisional biopsies are procedures in which the entire tumor is removed.

Cytology Tests

Cytology tests look for cancerous cells in bodily fluids.

Examples of fluids that can be examined with cytology tests 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 uses cervical tissue. The mouth, esophagus, bronchi, and stomach can also be scraped and brushed for cells.

Other Tests

After you've been diagnosed, your healthcare provider 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

Imaging tests produce pictures of internal areas of your body. These pictures help your healthcare provider see if there are tumors or changes that could be caused by cancer.

X-Rays

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 contrast dye is used 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 pictures of your body from different angles, producing cross-sectional images.

You might be given a special contrast dye, usually injected in a vein, to make the pictures clearer or to help your healthcare provider see the outline of a specific structure.

Ultrasound

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

Ultrasounds can also help healthcare providers guide needles during a fine-needle aspiration or a core biopsy.

Magnetic Resonance Imaging (MRI) Scan

Magnetic resonance imaging (MRI) scan creates cross-sectional images of your body by using magnetic fields and radio waves to create high-resolution pictures.

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

Mammography

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

Before having a mammogram or any other type of X-ray, let your healthcare provider 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 special precautions to avoid or reduce your baby's radiation exposure.

Nuclear Medicine Scans 

These tests help healthcare providers find tumors and correctly stage cancers. They use radionuclides that may be swallowed, inhaled, or injected and 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 healthcare provider 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 healthcare provider 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 can sometimes detect cancer before a person has any signs or symptoms.

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

People who are at increased risk for certain cancers may need regular screening. For people who don't have specific risk factors, certain routine screenings may be recommended at a designated age.

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

Breast Cancer

Breast cancer can be screened in the following ways.

  • Mammogram: The scan can show tumors and detect irregularities.
  • Self-examination: Checking your own breasts at home for changes in shape or size can help you get an early diagnosis.
  • Physical examination: Your healthcare provider can look at and physically examine your breasts.
  • Breast MRI: This type of MRI is designed 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 and advanced up to allow your healthcare provider to see inside the rectum and large intestine.
  • Stool DNA test: Analysis of your stool can detect DNA changes that are 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, makes the colorectal area show up more clearly.
  • Fecal occult blood test (FOBT): This test 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, can be tested for abnormal cell changes.
  • HPV test: The scraped cervical sample is tested for human papillomavirus (HPV)—a sexually transmitted infection that strongly increases a woman’s risk of cervical cancer. Your healthcare provider may 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 healthcare provider about routine prostate cancer screenings by the age of 55.

  • Digital rectal examination: Your healthcare provider inserts a gloved finger into your rectum to examine your prostate for structural abnormalities.
  • Prostate-specific antigen (PSA) test: A blood test is used to measure the level of the prostate-specific antigen in your body. Higher than normal levels may indicate prostate cancer.

People who are at 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. The US preventative services task force (USPSTF) has determined that there is not enough evidence to recommend for or against routine skin cancer screening by a healthcare provider.

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 healthcare provider.

  • Physical examination: Your healthcare provider 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 healthcare provider 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 unneeded medical care.

While screening tests can help diagnose cancer, they are not perfect. Sometimes, the tests do not detect cancer that is present. Other times, the tests are positive for cancer, even when someone doesn't have it. 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, it can be expensive to have follow-up diagnostic tests that aren't necessary.

If you regularly do self-checks at home and are concerned about cancer, talk to your healthcare provider. They will be able to help you understand your risk, as well as the risks of the tests that are used to diagnose 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 healthcare provider can definitively diagnose cancer and determine its stage (how advanced it is). There are home screening tests for colon cancer, such as Cologuard, for people who are at average risk of the disease. And you can use self-exams 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 extremely slow-growing cancer is carcinoid tumor, which can develop anywhere you have 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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Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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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.