What is a prognosis?

A prognosis is an estimate of the likely course and outcome of a disease. The prognosis of a patient diagnosed with cancer is often viewed as the chance that the disease will be treated successfully and that the patient will recover.

What factors affect a patient’s prognosis?

Many factors can influence the prognosis of a person with cancer. Among the most important are the type and location of the cancer, the stage of the disease (the extent to which the cancer has spread in the body), and the cancer’s grade (how abnormal the cancer cells look under a microscope—an indicator of how quickly the cancer is likely to grow and spread).

Other factors that affect prognosis include the biological and genetic properties of the cancer cells (these properties, which are sometimes called biomarkers, can be determined by specific lab and imaging tests), the patient’s age and overall general health, and the extent to which the patient’s cancer responds to treatment.

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How do statistics contribute to predicting a patient’s prognosis?

In estimating a cancer patient’s prognosis, doctors consider the characteristics of the patient’s disease, the available treatment options, and any health problems the patient may have that could affect the course of the disease or its ability to be treated successfully.

The doctor bases the prognosis, in large part, on information researchers have collected over many years about hundreds or even thousands of people with the same type of cancer. When possible, doctors use statistics based on groups of people whose situations are most similar to that of the patient.

Several types of statistics may be used to estimate a cancer patient’s prognosis. The most commonly used statistics are listed below.

  • Cancer-specific survival: This statistic calculates the percentage of patients with a specific type and stage of cancer who have survived—that is, not died from—their cancer during a certain period of time (1 year, 2 years, 5 years, etc.) after diagnosis. Cancer-specific survival is also called disease-specific survival. In most cases, cancer-specific survival is based on causes of death in medical records, which may not be accurate. To avoid this inaccuracy, another method used to estimate cancer-specific survival that does not rely on information about the cause of death is relative survival.
  • Relative survival: This statistic compares the survival of patients diagnosed with cancer (for example, breast cancer) with the survival of people in the general population who are the same age, race, and sex and who have not been diagnosed with that cancer. It is the percentage of cancer patients who have survived for a certain period of time after diagnosis relative to people without cancer.
  • Overall survival: This statistic is the percentage of patients with a specific type and stage of cancer who are still alive—that is, have not died from any cause—during a certain period of time after diagnosis.
  • Disease-free survival: This statistic is the percentage of patients who have no evidence of cancer during a certain period of time after treatment. Other similar terms are recurrence-free or progression-free survival.

Cancer survival statistics are frequently given in terms of 5-year survival relative to the general population (that is, as 5-year relative survival percentages or “rates”). For example, according to NCI’s Surveillance, Epidemiology, and End Results program, the 5-year relative survival rate for all women diagnosed with breast cancer during the period from 2001 through 2007 was 89 percent and the 5-year relative survival rate for all patients diagnosed with lung cancer during the same period was 16 percent.

Because survival statistics are based on large groups of people, they cannot be used to predict exactly what will happen to an individual patient. No two patients are entirely alike, and their treatment and responses to treatment can vary greatly. Also, because it takes years to see the impact of new treatments and diagnostic tests, the statistics a doctor uses to make a prognosis may not reflect the effectiveness of current treatments.

Nevertheless, the doctor may speak of a favorable prognosis if the information from large groups of people suggests that the cancer is likely to respond well to treatment. A prognosis may be unfavorable if the cancer is likely to be difficult to control. It is important to keep in mind, however, that a prognosis is only an estimate. Again, doctors cannot be absolutely certain about the outcome for an individual patient.