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  • A disease in which cells begin to grow and multiply uncontrollably
  • Types include carcinoma, leukemia, lymphoma, melanoma, multiple myeloma, and sarcomas among others
  • Treatments include surgery, chemotherapy, radiation therapy, immunotherapy, hormone therapy, and targeted therapy
  • Involves Yale Cancer Center, medical oncology, surgical oncology, Smilow interventional oncology program



According to the National Cancer Institute, an estimated 1.9 million Americans will be diagnosed with some form of cancer in 2022. Ultimately, cancer touches nearly everyone’s life in some way. Whether for screenings, assessment of worrisome symptoms, diagnosis, or treatment, eventually we all need to better understand this disease. 

As with most things, knowledge is power. The more you know about cancer, the better equipped you'll be to help yourself or a loved one who is awaiting a biopsy result or has already heard the words no one ever wants to hear: "It's cancer."

Getting diagnosed with cancer is scary, but it is important to know that it can be a survivable disease. With new, improved treatments and targeted therapies, people with many forms of cancer are living longer and healthier lives than ever before.

“Cancer treatment has made substantial progress in recent years,” says Kevin Billingsley, MD, MBA, chief medical officer for Smilow Cancer Hospital. “The traditional treatments, including chemotherapy, radiation, and surgery, have all become less toxic, less invasive, and more accurate. In addition, new treatments, including an entire class of medications that leverage the immune system, have revolutionized the treatment of many cancers.”

What is cancer?

Cancer is a disease that develops when cells grow and multiply uncontrollably. The human body is made up of trillions of cells. As cells get older, they can become damaged or die. Normally, the body makes new cells to replace damaged or dead ones. This process is carefully controlled to ensure that the new cells are healthy, and grow and divide properly.

In cancer, genetic changes (known as mutations) occur in a single cell. These changes disrupt the carefully controlled process of cell growth and division, and the affected cell begins to grow and multiply in an uncontrolled manner. Over time, the new cells can form a solid mass of tissue, known as a tumor.

Not all tumors are cancerous. Benign tumors, for instance, are not cancerous, and their cells cannot invade nearby tissues or spread to other parts of the body.

Malignant tumors, however, are cancerous, and the cells that make up malignant tumors are capable of invading nearby tissues and spreading through the blood or lymph system to distant areas of the body where they may form new tumors. When cancer cells spread from the primary tumor site and form a tumor elsewhere in the body, it is known as metastasis. This type of cancer is called metastatic cancer.

What are the different types of cancer?

Cancer is classified based on the part of the body in which it develops and by the type of cell involved.

Cancer classification by site. Cancer can develop in almost any part of the body, and most cancers are named based on the organ or tissue in which they develop. For instance, prostate cancer begins in the prostate gland and breast cancer begins in the breast. In all, there are over 100 different types of cancer.

Cancer classification by cell type. The body is made up of many types of cells. Doctors divide cancer into different categories depending on the type of cell in which the cancer began. Some of these categories include:

  • Carcinomas begin in epithelial cells. These cells line the organs, blood vessels, glands, and skin. Around 80 to 90% of cancers are carcinomas.
  • Sarcomas start in cells that make up bone and soft tissues, such as muscle, tendons, cartilage, and fat.
  • Leukemias begin in the bone marrow and blood cells. Leukemias do not form solid tumors.
  • Lymphomas begin in a type of white blood cells known as lymphocytes.
    Myelomas, also known as multiple myelomas, begin in white blood cells in the bone marrow called plasma cell
    Melanomas begin in melanocytes. These cells produce melanin, a pigment, in the skin.

What are the risk factors for cancer?

The risk factors for cancer include:

  • Age (older people are at higher risk)
  • Radiation exposure (e.g., X-rays, radon, ultraviolet radiation from sunlight)
  • Exposure to cancer-causing substances (e.g., asbestos, diesel exhaust, and secondhand smoke among others)
  • Family history of cancer
  • Certain infections (e.g., human papillomavirus (HPV) and Epstein-Barr virus (EBV) among others)

People can reduce their chances of getting cancer by making healthy lifestyle choices and avoiding certain factors that have also been associated with increased risk for cancer:

  • Tobacco use
  • Alcohol consumption
  • Obesity
  • Physical inactivity
  • Unhealthy diet (i.e., a diet high in red and processed meat, high-sugar drinks and snacks, and highly processed foods)

What is cancer screening?

Screening tests are used to detect cancer before symptoms develop. They can help doctors find cancers in their early stages, when they are most treatable. Common screening tests include:

  • Mammography. This procedure uses low-dose X-rays to produce an image of the breasts. It is widely used to detect breast cancer.
  • Pap test. This test, sometimes called a Pap smear, is used to detect cervical cancer.
  • HPV test. This test checks for high-risk HPV infection in women. Although HPV can infect both men and women and can lead to various kinds of cancer (cervical, penile, anal, vulvar, and oral and throat cancers, for example), the Food and Drug Administration- (FDA) only approves HPV screening tests for the detection of HPV infections of the cervix.
  • Colonoscopy. This test is used to detect colorectal cancer.
  • Screening CT Scan.  This test is used to detect lung cancer in early stages.

If these or other screening tests detect an abnormality, a doctor will order further tests to determine if cancer is present. 

How is cancer diagnosed?

Cancer is often first suspected when a patient notices symptoms or based on the results of a screening test for certain types of cancer such as a mammogram or routine pelvic exam.

Diagnosis of cancer typically begins with a review of the patient’s medical history and a physical examination. Doctors will ask about symptoms and whether the patient has any known risk factors for cancer. During the physical exam, the doctor will check for signs and symptoms of cancer.

Additional tests are necessary to confirm whether a patient has cancer and to determine the type and stage of cancer. These diagnostic tests may include:

  • Blood and urine tests. These tests allow doctors to measure the levels of different substances in blood and urine. Abnormal levels of certain substances may be a sign of cancer.
  • Imaging tests. These tests produce images of tissues inside the body. There are several types of imaging tests including X-rays, magnetic resonance imaging (MRI) studies, computed tomography (CT) scans, ultrasounds, bone scans, positron electron tomography (PET) scans, and radionuclide scans.
  • Biopsy. In this procedure, a health care provider removes a piece of tissue (usually from the tumor site). The tissue sample is then analyzed under a microscope by a pathologist to check for the presence of cancerous cells. A biopsy is necessary for the diagnosis of most types of cancer.

If cancer is diagnosed, the doctor may order some additional blood or imaging tests to determine the stage of the disease.

What are the stages of cancer?

The stage refers to tumor size and location, the extent of cancer spread in the body, and characteristics of the cancer cells. Knowing the stage of a cancer helps doctors customize treatment plans for each individual patient.

Many types of cancers are staged based on the TNM system. This system describes the tumor (T) and denotes whether the cancer has spread to the lymph nodes (N) or has spread—or metastasized (M)—to other parts of the body.

After doctors have determined the TNM status of a cancer, they may assign it to an overall stage as follows:

  • Stage 0. Abnormal cells are detected but they have not spread. This is a precancerous condition: The cells are not cancerous, but they may become cancerous. This stage is also called carcinoma in situ.
  • Stage I. The tumor is small and has not spread beyond the original site.
  • Stage II and III. The tumor is larger than in stage I and may have spread to the lymph nodes.
  • Stage IV. The cancer has spread to other parts of the body. This is known as metastatic cancer.

In general, treatment is more effective when the cancer is at a lower stage.

How is cancer treated?

Common types of cancer treatment include:

  • Surgery. Surgery is used to remove a cancerous tumor from the body. Sometimes it is not possible to remove the entire tumor. In these cases, a surgeon will remove part of the tumor to reduce its size. This is known as “debulking.”
  • Chemotherapy. Chemotherapy uses drugs to destroy or damage cancer cells to stop or slow their growth.
  • Radiation therapy. This treatment uses high doses of radiation to kill and damage cancer cells to prevent them from growing and spreading.
  • Targeted therapy. This therapy uses drugs that target specific components of cancer cells that are not found in noncancerous cells. Because the drugs target only cancer cells, they are unlikely to harm other cells. 
  • Immunotherapy. This treatment uses drugs to stimulate or suppress the patient’s own immune system with the aim of improving its ability to fight cancer. 
  • Stem cell transplant. Chemotherapy drugs can kill or damage healthy blood stem cells in the bone marrow. This interferes with the body’s ability to make new blood cells. A stem cell transplant, also known as a bone marrow transplant, replaces dead or damaged stem cells with healthy ones, thereby restoring the body’s blood-producing capacity.
  • Chimeric Antigen Receptor T-Cell (CAR-T) Therapy.   A type of treatment in which a patient’s immune cells (T- Cells) are collected and modified in a laboratory and then returned to the patient to treat cancerous cells.
  • Hormone therapy. Hormone receptor-positive cancer cells have hormone receptors that allow cancer cells to attach to hormones that circulate in the bloodstream. The hormones help these cancer cells grow. Hormone therapy is used to slow or stop the growth of hormone-receptor positive cancers.

What is the outlook for people with cancer?

The outlook for people with cancer varies greatly depending on a number of factors including the timing of diagnosis, the type of cancer, its stage, how aggressive it is, how well it responds to treatment, and a person’s age and overall health. In most cases, cancers that are caught early are easiest to treat and tend to have the best outcomes. Though cancer is a serious disease, it is treatable, and, in many cases, it can be cured.

With treatment, cancer may go into remission. Partial remission means that the cancer responded to treatment and has been reduced in size, but symptoms may still be present. Complete remission means that symptoms are not present and diagnostic tests are unable to detect cancer in the body.

In both cases, ongoing treatment may be necessary, and even cancers in complete remission may come back. Because of this, it is essential that after treatment, people continue see their doctor regularly to keep an eye on a possible recurrence of the cancer.

What makes Yale Medicine's approach to cancer unique?

“As a National Cancer Institute-designated Comprehensive Cancer Center, the treatment approach at Yale Cancer Center and Smilow Cancer Hospital is marked by team-based care, which brings together the expertise of a complete group of specialists to treat cancer from the earliest stages through advanced disease,” says Dr. Billingsley. “Research is central to all clinical care at Smilow Cancer Hospital and our Smilow Cancer Hospital Network. Clinical trials provide patients with access to the most advanced array of drugs and treatments. These services are available to patients not only in New Haven but to those throughout Connecticut through the Smilow Cancer Hospital Care Network.”