The 5-year relative survival rate for all cancers diagnosed in 2004-2010
was 68%, up from 49% in 1975-1977 (see page 18). The improvement in survival
reflects both the earlier diagnosis of certain cancers and improvements in
treatment. Survival statistics vary greatly by cancer type and stage at
diagnosis. Relative survival is the percentage of people who are alive a
designated time period after a cancer diagnosis (usually 5 years) divided by
the percentage expected to be alive in the absence of cancer based on normal
life expectancy. It does not distinguish between patients who have no evidence
of cancer and those who have relapsed or are still in treatment. While 5-year
relative survival is useful in monitoring progress in the early detection and
treatment of cancer, it does not represent the proportion of people who are
cured because cancer deaths can occur beyond 5 years after diagnosis. In
addition, although relative survival provides some indication about the average
survival experience of cancer patients in a given population, it may not
predict individual prognosis and should be interpreted with caution. First,
because 5-year relative survival rates for the most recent time period are
based on patients who were diagnosed from 2004 to 2010, they do not reflect the
most recent advances in detection and treatment. Second, factors that influence
individual survival, such as treatment protocols, other illnesses, and
biological or behavioral differences in cancers or people, cannot be taken into
account. Third, survival rates may be misleading for cancers detected before
symptoms arise if early diagnosis does not extend lifespan. This occurs when
cancer is diagnosed that would have gone undetected in the absence of screening
(overdiagnosis) or when early diagnosis does not alter the course of disease.
In other words, increased time living after a cancer diagnosis does not always
translate into progress against cancer. For more information about survival
rates, see “Sources of Statistics
How Is Cancer Staged?
Staging describes the extent or spread of cancer at the time of
diagnosis. Proper staging is essential in determining the choice of therapy and
in assessing prognosis. A cancer’s stage is based on the size or extent of the
primary tumor and whether it has spread to nearby lymph nodes or other areas of
the body. A number of different staging systems are used to classify cancer. A
system of summary staging is used for descriptive and statistical analysis of
tumor registry data and is particularly useful for looking at trends over time.
According to this system, if cancer cells are present only in the layer of
cells where they developed and have not spread, the stage is in situ. If cancer
cells have penetrated beyond the original layer of tissue, the cancer has become
invasive and is categorized as local, regional, or distant based on the extent
of spread. (For a more detailed description of these categories, see the
footnotes in the table “Five-year Relative Survival Rates (%) by Stage at
Diagnosis, US, 2004-2010” on page 17.) Clinicians use a different staging
system, called TNM, for most cancers. The TNM system assesses cancer growth and
spread in 3 ways: extent of the primary tumor (T), absence or presence of regional
lymph node involvement (N), and absence or presence of distant metastases (M).
Once the T, N, and M categories are determined, a stage of 0, I, II, III, or IV
is assigned, with stage 0 being in situ, stage I being early, and stage IV
being the most advanced disease. Some cancers (e.g., leukemia and lymphoma)
have alternative staging systems. As the biology of cancer has become better
understood, genetic features of tumors have been incorporated into treatment
plans and/or stage for some cancer sites.
