Overall Survival (OS)

Overal survival rates are one important measure of survival.

The Basic Concept

Overall survival, or OS, or sometimes just “survival” is the percentage of people in a group who are alive after a length of time – usually a number of years.

     For example: “The 5-year OS for stage II Hodgkin lymphoma is about 90 percent.”

This means that, of all patients with Hodgkin lymphoma that researchers were watching in their study, those who lived at least 5 years from the time of diagnosis comprised 90 percent.

The 5-year OS is often reported for people known to have a particular particular stage of cancer, or sometimes people having a particular stage of cancer who received a specific treatment of interest. So, in these cases, it might be specified that the 5-year OS rates reflect the percentage of people who are living 5 years after diagnosis or 5 years after the start of therapy.

Survival versus Cure

In a sense, OS can be reflective of cure rates, but this is not always the case. Different “yardsticks” are used to measure survival in cancer patients, and each one has its own strengths and limitations. The 5-year OS is used for many cancers including high-grade lymphomas in view of the fact that those who do survive 5 years are likely to be cured of their disease. In some slow growing and low-grade malignancies like follicular lymphoma, however, the 10-year overall survival may be more reflective of what would be considered a cure.

In other words, being alive 5 years after a diagnosis of follicular lymphoma doesn’t necessarily mean the disease is gone for good.

Survival versus Cause-Specific Survival

When information about cause of death is added in, this may be referred to as a corrected survival or cause-specific survival. Cause-specific survival has the potential to be very different from OS.

The cause-specific survival is considered a more valid way to estimate how much extra death in a group there is due to the cancer itself. For instance, consider a cancer that is mainly found in people who also have bad heart disease. If you only look at overall survival and not cause-specific survival — you don’t know anything about the number of deaths due to heart disease, and not cancer—and this can make it seem like a cancer is more lethal than it actually is.

Survival by Prognostic Groups

Sometimes people with cancer are put into different groups to get a better picture of survival. These groups may be referred to as prognostic groups. Let's take follicular lymphoma as an example.

According to the American Cancer Society, for follicular lymphoma, the Follicular Lymphoma International Prognostic Index or FLIPI was developed because the existing prognostic index was insufficient. There is the plain old International Prognostic Index , or IPI, which is useful for many lymphomas, but it’s not as helpful for follicular lymphomas, which tend to be slower growing.

The FLIPI uses slightly different prognostic factors than the IPI, as follow:

Good prognostic factors

·       Age 60 or below

·       Stage I or II

·       Blood hemoglobin 12 g/dL or above

·       4 or fewer lymph node areas affected

·       Serum LDH is normal

Poor prognostic factors

·       Age above 60

·       Stage III or IV

·       Blood hemoglobin level below 12 g/dL

·       More than 4 lymph node areas affected

·       Serum LDH is high

Patients are assigned a point for each poor prognostic factor. People without any poor prognostic factors would have a score of 0, while those with all poor prognostic factors would have a score of 5. The index then divides people with follicular lymphoma into 3 groups:

·       Low risk: no or 1 poor prognostic factor(s)

·       Intermediate risk: 2 poor prognostic factors

·       High risk: 3 or more poor prognostic factors

The study used to develop the FLIPI reported the following survival rates:*

·       Low-risk: 5-year OS of 91 percent; 10-year OS of 71 percent

·       Intermediate-risk: 5-year OS of 78 percent; 10-year OS of 51 percent

·       High-risk: 5-year OS of 53 percent; 10-year OS of 36 percent

* The American Cancer Society notes the following disclaimer:
These rates reflect the number of people who lived for at least 5 or 10 years after being diagnosed – many people lived longer than this. The rates were based on people diagnosed with follicular lymphoma in the 1980s and 1990s. Newer treatments have been developed since then, so current survival rates are likely to be higher.”

A Word from Verywell

Survival rates are good tools, but in some ways, they are like yellowed newspapers – since they take years to develop, they are true for a specific time frame and reflect the treatment used at that time. For a person starting a new therapy today a published 10-year overall survival rate may or may not be relevant.

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