SEER Training Modules

Cancer Diagnosis

The diagnosis of cancer entails an attempt to accurately identify the anatomical site of origin of the malignancy and the type of cells involved. Cancer can arise in any organ or tissue in the body except fingernails, hair, and teeth.

The site refers to the location of the cancer within the body. The body part in which cancer first develops is known as the primary site. A cancer's primary site may determine how the tumor will behave; whether and where it may spread (metastasize) and what symptoms it is most likely to cause. The most common sites in which cancer develops include the skin, lungs, female breasts, prostate, colon and rectum, and corpus uteri.

Secondary site refers to the body part where metastasized cancer cells grow and form secondary tumors. A cancer is always described in terms of the primary site, even if it has spread to another part of the body. For instance, advanced breast cancer that has spread to the lymph nodes under the arm and to the bone and lungs is always considered breast cancer (and the spread to the lymph nodes, bones, and lungs describe the stage of the cancer).

As is the case with other medical conditions, there are many signs and symptoms that may indicate the presence of cancer. These may be observed directly, through imaging technologies, or confirmed by lab tests. However, these signs and symptoms of cancer may resemble those of other conditions. For example, weight loss and abdominal pain can be caused by stomach cancer or an ulcer. Pink or reddish urine can be caused by kidney cancer or a kidney infection. A positive fecal occult blood test can indicate a variety of intestinal problems. A biopsy (removal of tissue for microscopic evaluation) is preferred to establish, or rule out, a diagnosis of cancer.

Tissue samples can be easily retrieved from a tumor near the body's surface. If the mass is inaccessible, an imaging exam that enables a tumor to be located precisely and visualized may be ordered before the biopsy is performed.

The histological type is determined by microscopic examination of suspected tissue that has been excised by biopsy or surgical resection. If the histological type is different from what is usually found in the tissue being examined, it can mean the cancer has spread to that area from some primary site. Metastasis can occur by direct extension, via the blood stream or the lymphatic system, or by seeding or implantation of cancer cells.

A biopsy, together with advanced imaging technologies, may not only confirm the presence of cancer, but may also pinpoint the primary site and secondary site(s).

It is also important to identify the cell type(s). Various histological types have different growth rates and dissimilar prognoses. More than one histological type of cell may be found in the same site. For example, a tumor whose primary site is skin can be a basal cell carcinoma, a squamous cell carcinoma, or a melanoma.

Once cancer has been confirmed, the pathologist tries to determine how closely the cancer cells resemble healthy, mature cells. Such cells are said to be differentiated. Cancer cells that do not look like their healthy counterparts are called undifferentiated, or, because they often look like very immature cells, primitive. The pathologist assigns a pathological grade to a tumor according to how aggressive the tissue looks under the microscope. Tumor grades can be expressed in words or by a number. One set of terms consists of well differentiated (grade 1), moderately differentiated (grade 2), poorly differentiated (grade 3), or undifferentiated (grade 4). When tumors are graded by number (1 through 4), a grade-1 tumor has a better natural history than a grade-4 tumor does.

Cancers are further classified according to stage. Staging describes how far a cancer has progressed based on the size of the primary tumor and whether and/or where it has spread. Go to the Summary Staging and Summary Stage 2000 training module for more details on cancer staging.

In summary, a biopsy is the preferred method to confirm the diagnosis of cancer. Biopsies can provide information about histological type, classification, grade, potential aggressiveness and other information that may help determine the best treatment. More information regarding cancer treatment is provided in the Cancer Treatment training module.