Cancer testing spans a wide range of methods, from routine screening tests you get before any symptoms appear to targeted diagnostic procedures that confirm whether a suspicious finding is actually cancer. The specific tests depend on the type of cancer being investigated, but most follow a general path: screening or physical exam first, then imaging, blood work, and ultimately a biopsy to examine cells under a microscope. A biopsy is the only test that can definitively diagnose cancer.
Physical Exams and What Doctors Look For
A cancer workup often begins with a hands-on physical examination. Your doctor checks for lumps, swollen lymph nodes, changes in skin color or texture, and whether any mass feels fixed to surrounding tissue. For suspected gastrointestinal cancers, the exam includes pressing on the abdomen to feel for organ enlargement. Lymph nodes in the neck, armpits, and groin are commonly checked by hand, since swollen or hardened nodes can signal that cancer has spread from a nearby site.
Physical exams have limits. Not all lymph nodes sit close enough to the surface to be felt, and enlarged nodes aren’t assumed to contain cancer until a sample confirms it. But a thorough exam helps guide which imaging or lab tests come next.
Routine Screening Tests
Screening tests are designed to catch cancer early, before you notice anything wrong. The major ones recommended in the U.S. are based on age, sex, and risk factors.
Mammography for breast cancer is recommended every two years for women aged 40 to 74. The test uses low-dose X-rays to detect masses or calcifications in breast tissue that are too small to feel.
Colorectal cancer screening starts at age 45. You have several options. Colonoscopy lets a doctor visually inspect the entire colon and remove precancerous growths during the same procedure. Its sensitivity for detecting large adenomas (the growths most likely to become cancer) ranges from 89% to 95%. Stool DNA tests, which you complete at home, detect 93% of colorectal cancers but are less effective at catching precancerous growths, picking up about 43% of advanced adenomas. A positive stool test still requires a follow-up colonoscopy.
Cervical cancer screening uses either a Pap smear, an HPV DNA test, or both. HPV testing is significantly more sensitive, catching about 96% of precancerous cervical changes compared to roughly 53% for a Pap smear alone. The tradeoff is slightly more false positives: HPV testing’s specificity is around 91%, while a Pap smear’s is about 96%.
Lung cancer screening with a low-dose CT scan is recommended annually for adults aged 50 to 80 who have a 20 pack-year smoking history and either currently smoke or quit within the past 15 years. A pack-year means smoking one pack per day for one year, so 20 pack-years could be one pack a day for 20 years or two packs a day for 10.
Imaging Tests
When screening raises a concern or symptoms point toward cancer, imaging tests help locate tumors, determine their size, and check whether cancer has spread.
CT scans use computer-controlled X-rays to create cross-sectional images of the body. You may drink or be injected with a contrast agent that makes the boundaries between organs and tumors easier to see. CT scans are particularly useful for the chest, abdomen, and pelvis.
MRI uses strong magnets and radio waves instead of radiation. It produces highly detailed images of soft tissue, making it especially valuable for brain, spinal cord, and joint imaging. An MRI session typically takes longer than a CT scan, sometimes 30 to 60 minutes.
PET scans work differently from CT or MRI. A small amount of a radioactive sugar compound is injected into your bloodstream. Cancer cells consume sugar faster than normal cells, so they light up on the scan. PET scans are particularly good at revealing whether cancer has spread to distant parts of the body and are often combined with CT scans for a more complete picture.
Ultrasound uses sound waves to create real-time images of organs. It’s commonly used to evaluate lumps in the breast, thyroid, or liver, and to guide a needle during biopsies. Ultrasound doesn’t work as well for the brain, lungs, or large areas of the abdomen and pelvis, where CT or MRI are more reliable.
Blood Tests and Tumor Markers
Blood tests alone cannot diagnose most cancers, but they play important supporting roles. A complete blood count can reveal abnormalities associated with blood cancers like leukemia. Liver and kidney function tests can suggest that cancer may be affecting those organs.
Tumor markers are proteins or other substances that some cancers release into the bloodstream. Common examples include PSA (used for prostate cancer), CA-125 (ovarian cancer), CEA (colorectal and other cancers), and AFP (liver cancer and certain germ cell tumors). These markers are most useful for tracking how well treatment is working or detecting recurrence after treatment. They’re less reliable as standalone diagnostic tools because noncancerous conditions can also raise their levels.
Biopsy: The Definitive Test
Imaging and blood tests can strongly suggest cancer, but a biopsy is what confirms it. During a biopsy, a small sample of tissue is removed and examined under a microscope by a pathologist.
There are several types. A fine-needle aspiration uses a thin needle and syringe to draw out fluid and cells from a suspicious area. It’s quick and minimally invasive, often used for thyroid nodules or breast lumps. A core needle biopsy uses a larger needle with a cutting tip to extract a small column of tissue, providing more material for analysis than a fine-needle approach. Both of these are typically done with local anesthesia in an outpatient setting.
A surgical biopsy is reserved for cases where needle biopsies can’t reach the suspicious area or haven’t provided a clear answer. A surgeon makes an incision to access the tissue and may remove part of the suspicious area or all of it. This is more involved and may require general anesthesia.
Endoscopic Procedures
Endoscopy lets doctors look directly inside hollow organs using a flexible tube with a camera. It serves double duty: visualizing abnormal tissue and taking biopsy samples through instruments passed through the scope.
A colonoscopy examines the colon. A bronchoscopy looks at the airways leading into the lungs, used when lung cancer is suspected. A cystoscopy inspects the bladder and urethra for signs of bladder cancer. Upper endoscopy examines the esophagus and stomach. During any of these, the doctor can remove small tissue samples or even entire small growths for testing.
Genetic Testing for Cancer Risk
Genetic tests don’t detect existing cancer. Instead, they identify inherited mutations that significantly raise your lifetime risk of developing certain cancers. The best known are changes in the BRCA1 and BRCA2 genes, which produce proteins that help repair damaged DNA. When these genes carry harmful mutations, cells lose a key safeguard against uncontrolled growth.
The numbers are striking. More than 60% of women with a harmful BRCA1 or BRCA2 change will develop breast cancer in their lifetime, compared to about 13% of women overall. For ovarian cancer, the risk jumps to 39% to 58% with a BRCA1 mutation, versus about 1.1% in the general population. These mutations also raise the risk of pancreatic and prostate cancer in both men and women who carry them.
About 1 in 400 people in the general population carry a harmful BRCA change, but the rate is roughly 10 times higher (about 2%) among people of Ashkenazi Jewish descent. Genetic testing is typically recommended when family history suggests an inherited pattern, such as multiple close relatives diagnosed with breast, ovarian, or related cancers at young ages. A positive result can lead to more frequent screening, preventive medications, or risk-reducing surgery.
Liquid Biopsies
Liquid biopsy is a newer approach that analyzes blood samples for fragments of tumor DNA, whole tumor cells, or other cancer-related molecules circulating in the bloodstream. One FDA-approved system, CellSearch, detects circulating tumor cells and is used to monitor metastatic breast, prostate, and colorectal cancers. Another, FoundationOne Liquid CDx, profiles tumor DNA from a blood draw to identify specific genetic changes that can guide treatment decisions.
These tests are currently used more for monitoring known cancers and selecting targeted therapies than for initial diagnosis. For example, in non-small cell lung cancer, circulating tumor DNA has been detected in 100% of patients with stage II through IV disease, but only 50% of stage I patients. That gap means liquid biopsies aren’t yet reliable enough to replace traditional methods for early detection across all cancer types, though they’re increasingly valuable as a less invasive complement to tissue biopsies.