What is a cancer diagnosis?

Diagnosis is not the same as detection. Cancer may be detected when symptoms or abnormalities, such as a lump or growth, are recognized by a patient or doctor. After a cancer is detected, it still must be carefully diagnosed.
A diagnosis is an identification of a particular type of cancer. When making a diagnosis, the initial signs and symptoms are investigated through a variety of tests in order to identify whether cancer is causing them and, if so, what type of cancer it is. For example, breast cancer may be detected when a patient notices a lump, but it must be carefully evaluated with a number of tests in order to determine an accurate diagnosis. The diagnosis describes what type of breast cancer it is (i.e. 'ductal' if it started in the ducts of the breast or 'lobular' if it started in the lobes) and how advanced it is.

What is a cancer stage?

Following a diagnosis of cancer, the most important step is to accurately determine the stage of cancer. Stage describes how far the cancer has spread. (Some cancers, such as leukemia, may not be staged.) Each stage of cancer may be treated differently. In order for you to begin evaluating and discussing treatment options with your healthcare team, you need to know the correct stage of your cancer.
There are many staging systems, but TNM is the most common. 'T' refers to the size of the tumor, 'N' to the number of lymph nodes involved, and 'M' to metastasis. TNM staging measures the extent of the disease by evaluating these three aspects and assigning a stage, which is usually between 0-4. Generally, the lower the stage, the better the treatment prognosis (outcome).
  - Stage 0 - precancer
  - Stage 1 - small cancer found only in the organ where it started
  - Stage 2 - larger cancer that may or may not have spread to the lymph nodes
  - Stage 3 - larger cancer that is also in the lymph nodes
  - Stage 4 - cancer in a different organ from where it started

How is prognosis determined?

The probable course and/or outcome of the cancer is called the prognosis. Identifying factors that indicate a better or worse prognosis may help you and your doctor plan your treatment. There are many factors that help determine your prognosis. Some of these include:
  - Your age
  - Your level of physical fitness
  - Size of your cancer
  - Stage of your cancer
  - Aggressiveness of your cancer (cancer cells that are growing and dividing rapidly are considered more aggressive)

Your doctor will evaluate all possible factors to determine your prognosis.
Recently, the genetic make-up of cancer is being increasingly recognized as an important prognostic factor. For example, some genes have been associated with an aggressive course or tendency to recur. Identification of these in an early stage cancer may indicate a poor prognosis. Some research suggests that the genetic make-up of the cancer may be even more important for determining prognosis than the stage of the cancer.

How is cancer diagnosed?

Diagnosing cancer involves the use of a variety of tests that provide details about abnormal cells, which may have been detected through routine medical examinations, self-examination, or reported symptoms. More information about these cells must be gathered in order to identify them as malignant (cancerous) or non-malignant (non-cancerous), and if they are malignant, to determine how serious (aggressive) the particular cancer cells are. Aggressive cancers grow and spread more quickly than less-aggressive or 'indolent' cancers. There are many types of tests specifically designed to evaluate cancer:

  - A pathology report is based on observation of abnormal cells under a microscope.
  - Diagnostic imaging involves visualization of abnormal masses using high tech machines that create images, such as x-rays,
    computed tomography (CT), positron emission test (PET), magnetic resonance imaging (MRI), and combined PET/CT.
  - Blood tests measure substances in the blood that may indicate how advanced the cancer is or other problems related to the cancer.
  - Tumor marker tests detect substances in blood, urine, or other tissues that occur in higher than normal levels with certain cancers.
  - Special laboratory evaluation of DNA involves the identification of the genetic make-up-the DNA-of the abnormal cells.

How does diagnosis determine treatment?

Historically, a combination of pathological assessment (laboratory evaluation using a microscope) and diagnostic imaging has been used to identify the type of cancer and its stage, and then the treatment. Stage indicates how extensive the cancer is and how much it has spread. Staging usually involves determining the size of the primary tumor and evaluating whether it has remained in the tissue in which it started, whether it has invaded other nearby organs or tissues, and whether cancer cells have spread to distant locations in the body. The cancer is then assigned a stage on a predetermined scale of numbers and letters, for example stage I, II, IIIa, IIIb, IV, etc. The higher number and letter combination indicates more extensive spread, and therefore a more serious condition. Treatment is often selected based on the stage of disease. Higher stage cancers typically receive very aggressive treatments and lower stage disease less aggressive treatment.

However, research has indicated that identifying the stage of disease may not be the most accurate technique for determining how aggressive it is. For example, some early stage diseases may recur or progress even after treatment, while some late stage cancers may stay in remission. These findings suggest that there may be factors other than how the cancer looks under a microscope and how far it has spread at the time of diagnosis that may better indicate the likelihood that a given cancer will recur and/or progress.
Human genomics, which is the study of the entire genetic material of humans, has provided invaluable tools for identifying the genetic components of cancers. The mapping of the human genome, which consists of 30,000 to 70,000 genes, has laid the ground work for understanding the role those genes play in human health and disease. Cancer is many different diseases; however, one aspect of all cancers that is similar is damage to the DNA resulting in uncontrolled cell growth. Identifying the genes for each cancer type that are involved in the capacity grow and spread may provide valuable prognostic information.

As improvements are made in the special laboratory techniques used to identify the genetic make-up of cancers, this genetic information may become a better predictor of cancer aggressiveness and outcome than stage, which has been the diagnostic indicator of choice in the past. Additionally, this genetic information will likely play an increasing role in directing treatment. Specifically, the genes involved in each cancer may indicate more aggressive treatment for some cancers and less aggressive treatment for others.