How does a doctor diagnose cancer?
As a general rule, the earlier doctors can confirm a diagnosis in a person with cancer, the more likely it is that treatment will have powerful effects.
In this article, we examine the process for diagnosing cancer and the symptoms that can indicate when to see a doctor.
Laboratory testing can help identify the presence of a cancer.
Doctors will often use a combination of tests to determine whether a person has cancer. These tests indicate the presence of cancerous cells in the body and the extent to which these cells have spread.
Some of these tests include:
Biopsy: This involves taking a sample of tissue from a potentially cancerous lesion and sending it to a laboratory. A pathologist who specializes in diagnostic techniques will then examine the cells for signs of cancer.
A biopsy sometimes involves using a needle to remove cells, but a doctor might use a surgical procedure in instances where a larger area requires examination.
Imaging scans: These help a doctor identify cancerous lesions in the body. Examples of imaging studies include a CT, ultrasound, or MRI scan. Imaging machines have different methods of creating images and may be more sensitive to certain types of cancer, such as cancers of the soft tissue or bones.
A doctor may order more than one imaging scan for this reason.
Laboratory testing: Cancerous cells release compounds into the blood. A doctor may take samples of blood, urine, sputum, or other body fluids to check for these compounds. Lab tests are rarely a primary method for diagnosing cancer. However, they can be important for ruling out other conditions and confirming a diagnosis.
A doctor will usually work with a team of specialists to diagnose cancer, including a radiologist and pathologist.
Doctors classify cancer using the site at which the cancer started or the type of tissue where the cancer originated.
Examples of cancer classifications by tissue type include:
Carcinoma: This develops in epithelial tissues, such as those in the gastrointestinal tract or mucous membranes. According to the National Cancer Institute, an estimated 80 to 90 percent of cancer cases are carcinomas.
- Leukemia: This is a cancer that arises in the bone marrow, which produces blood cells.
- Lymphoma: This develops in the lymphatic system that includes the spleen, tonsils, and thymus. This system relates to immune activity and hormones.
- Mixed types: Mixed cancers develop in two different types of cell from one category or multiple categories.
- Myeloma: Often occurring in the bone marrow, this type originates in plasma cells that circulate as part of the blood.
- Sarcoma: These originate in connective tissue, developing in areas such as the bones, muscle, fat, and cartilage. Sarcomas are more common in young people.
Each type of cancer cell has a distinctive appearance that helps a doctor distinguish it from other cancers. Knowing the classification of cancer can help a doctor develop an effective plan for treatment.
More than 100 cancer types can occur. As a result, cancer causes a variety of symptoms depending upon the type.
Some cancers might not cause symptoms until reaching a more advanced stage, which is why early detection methods, such as skin cancer checks and mammograms, are recommended.
A changing mark or mole on the skin can be a sign of skin cancer.
Cancer symptoms usually create changes in the body that do not relate to a specific or identifiable cause. A person might incorrectly dismiss these as age-related changes when they indicate an early symptom of cancer.
- blood in the urine or stool
- changes to skin texture on the surface of a breast, nipple size, or breast shape
- vocal changes, such as hoarseness
- a persistent cough that does not respond to soothing measures
- difficulties in chewing and eating
- excessive tiredness and weakness
- profuse sweating during sleep
- urination problems, such as incontinence
- skin changes, such as a new mole or skin injury that does not heal
- stomach pain
- unexplained weight loss or gain
While cancer can cause pain, it is not usually an early symptom of cancer.
Seek a medical opinion if experiencing any of these symptoms without knowing the cause.
Cancer is often a dangerous condition, as cancer cells use up vital resources and space that would otherwise support other systems and functions.
Cancer cells use up oxygen, blood, and energy stores. Tumors that form from cancer cells can lead to the creation of new blood vessels, diverting blood flow. Cancer also compromises the immune system, reducing a person's ability to fight other illnesses and diseases.
In the United States, cancer is the second leading cause of death.
However, cancer is by no means always fatal, and developments in treatment have led to vastly improved survival rates and longer periods spent without cancer.
Outlook and stages
After receiving a cancer diagnosis, people often worry about the next steps and the likelihood of their cancer being dangerous.
Doctors use a system called staging to help determine a person's cancer prognosis and outlook. Staging takes into account many factors that determine the progression of cancer, such as tumor size and spread.
By using a consistent staging system, doctors across the world can understand more about cancer simply by knowing the stage.
Several factors come into consideration when staging a tumor, such as:
- the degree to which cells appear abnormal
- the spreading of cancer to nearby lymph nodes or other parts of the body
- the likelihood for the tumor to grow and spread
- the type of cells in the tumor
- the location of the tumor
- the size of the tumor
Doctors use this information and place it into the TNM staging system. The components of the system are:
T, for tumor: Doctors consider the size and extent of the main or primary tumor.
N, for number: This refers to the number of lymph nodes that also show signs of having cancerous cells. A higher number of lymph nodes with cancer cells will mean a more advanced stage.
M, for metastasis: Doctors consider if the cancer cells have spread to other body parts.
Staging can help a person define the next steps in their treatment.
An example of a tumor staging using this system could be T1N0MX. This means the primary tumor is identified, there is no cancer in the lymph nodes, and the doctor cannot measure the spread, or metastasis, of the cancer.
The TNM system can be very detailed. Another staging method a doctor might use for some cancers ranges from 0 to IV.
These stages mean:
- Stage 0: The doctor has found cancer cells or abnormal cells, but they have not spread to nearby tissue. Another name for stage 0 cancer is carcinoma in situ.
- Stages I, II, and III: A higher the number suggests a larger tumor or a wider spread to nearby tissues or lymph nodes.
- Stage IV: The cancer has spread to distant parts of the body. This is the most serious stage of cancer.
Additional staging systems exist, and a doctor may use them based on conventions in the location of their practice and the type of cancer.
Staging is an important part of defining the outlook for a person with cancer but does not provide the full picture of how likely that person is to survive.
A doctor will also consider other factors, including:
- a person's overall health
- the type of cancer
- how long ago a person received the diagnosis
When a doctor discusses the outlook with the person who has cancer, they might explain survival rates in various terms. Examples of these terms may include:
- Overall survival: This number refers to the percentage of people with a specific cancer type that survived for a certain period after their diagnosis.
- Disease-free survival: The percentage of people in a study or treatment group who have not died from a specific cancer over a certain period.
- Relative survival: This measurement compares the survival of cancer patients with the survival of people of the same sex and age who did not have cancer over a certain period of time.
None of these are absolutes. Some people survive longer than their predicted outlook, while others do not.
Diagnosing cancer in the early stages is vital for improving the chances of survival.
A doctor might use a biopsy, imaging scan, or blood test to confirm cancer. If cancer is present, they will then decide on the categorization and stage of it to determine how severe it is and shape the course of treatment.
Receiving a cancer diagnosis can be devastating. Taking the time to talk with a doctor and fully understand treatment options and prognosis can help a person move forward and make decisions about treatment.
Never ignore potential cancer symptoms. A person should talk with their doctor if they have observed any worrisome symptoms that are unexplained or persistent.
I have just received a diagnosis of cancer with a very poor outlook. What next?
Receiving a diagnosis of advanced cancer may be overwhelming and distressing. It’s important to talk with your doctor in detail about your specific diagnosis and treatment options to fully understand your prognosis.
You can also get a second opinion to help you decide how to move forward with treatment or palliative care. It’s important to reach out for support from family and friends, and it may help to bring someone to support you at doctor visits.Yamini Ranchod, PhD, MS Answers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.