Stable Disease in Cancer Treatment

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Cancer doctors use the term stable disease to describe a tumor that is neither growing nor shrinking. Specifically, it means that cancer has not increased in size by more than 50% or decreased in size by more than 30%. Stable disease also means that no new tumors have developed and that cancer has not spread to any new regions of the body (the cancer is not getting better or worse and has not metastasized further).

What does stable disease fall in the spectrum of treatment response, what are the limitations of this term, and what might stable disease mean with regard to your particular cancer? In other words, does stable disease mean that a treatment is working? These are important questions to answer, but it can be helpful to think about the natural history of cancer. A cancer that is not treated can often be expected to grow. Some people may be discouraged to hear that their cancer has not decreased significantly in size, but if that tumor had otherwise been expected to grow, "stable disease" may be a good thing.

Stable Disease Definition

To understand medical terms describing the response to treatment and survival rates, it can help to know where on a line the term follows. Stable disease would be defined as being a little better than progressive disease, which means that a tumor has increased in size by at least 20%, and a little worse than a partial response, which means that a tumor has decreased in size by at least 50%.

In other words, stable disease means that cancer has changed very little, and if it has changed, it has not grown more than 50% in size or decreased more than 30% in size. 

Limitations in Determining Change in Tumor Size

Why would a tumor be considered stable if it has, for example, increased in size by 10% to 20%? The primary reason is that the techniques we have to determine the size of a tumor are limited by our ability to visualize tumors indirectly, as with imaging tests such as CT scans and PET scans. The size of a tumor may appear slightly different for two different radiologists reading the same films, or the tumor may be looked at from slightly different angles at different times the scans are done.

Does Stable Disease Mean a Treatment is Not Working?

Stable disease doesn't necessarily mean that a treatment isn't working. What it means can vary significantly depending on the type of tumor you have, the particular treatment you are receiving, and your progress with other treatments in the past. Stable disease may mean that a treatment isn't working, but it may also mean that a treatment is working very well.

If a tumor would be expected to have grown in the interval between two scans and has remained stable, it may mean that the treatment is working well—even if there is not much of a change seen on scans. Cancer may also be stable—and the treatment working—if it's expected that the tumor would have spread to another region of the body at the time of the second scan.

Stable Disease in Clinical Trials and Targeted Therapies

Up until the last decade or so, clinical trials often required evidence of a 20% reduction in tumor size to say that a cancer treatment was actively working. This has changed, however, especially with respect to targeted therapies. Targeted therapies are drugs that specifically target pathways in the growth of cancer to stop the growth and spread of cancer. They do not, however, usually "cure" the cancer. When looking at these treatments, better indications of a treatment response are often "progression-free survival" and an "overall survival benefit." In other words, doctors are increasingly looking for treatments that provide meaningful outcomes for people, rather a certain percentage reduction in tumor size.

Stable Disease and Immunotherapy

Stable disease can also be a good sign with immunotherapy. We've been trained, in many ways, to expect a prompt response to cancer treatments. Chemotherapy drugs, for example, almost instantly kill cancer cells and may result in a rapid response (though of limited duration with most advance cancers).

Immunotherapy drugs, however, work in a different way. These drugs work by essentially taking the breaks off the immune system so our own immune cells can fight cancer. It takes time for the immune system to recognize cancer cells and then travel to a tumor and/or metastases to work.

There is another phenomenon seen with immunotherapy that can also affect response—or at least what appears to be the response seen on imaging studies. The concept of "pseudoprogression" was first noted in 2016 in which cancers that will later respond to treatment appear to worsen initially. It's now thought that the accumulation of immune cells around the tumor may give the appearance on CT and PET scans that a tumor has increased, while actually it has improved. Biopsy specimens of these areas have shown tumors surrounded by immune cells, and in some cases, the tumor has disappeared completely. What this means for people with "stable disease" at times, is that patience is needed (something easier said than done).

Other Terms Describing Cancer Response to Treatment

It can be helpful to define a few other terms that your oncologist may use in describing your response to cancer treatment.

  • The terms no evidence of disease (NED), complete response, and complete remission mean that no sign of cancer is present on any imaging studies. They do not mean the cancer is gone, just that, with the technology we currently have, no cancer can be found.
  • The term recurrence means that cancer has come back after being NED or in remission. 
  • The term response means that at treatment appears to be working and can be defined as a minor response (it decreased the size of a tumor by 25 percent to 50 percent) a partial response (it decreased the size of a cancer or the spread of a cancer, or the two combined by at least 50 percent) or a complete response (no evidence of cancer remains).
  • The term progressive disease means that a cancer is getting worse. and that it has increased or spread by more than 50 percent.
  • The term clinical benefit may mean that a tumor has decreased in size, or may just mean that the size of a tumor has remained stable if would otherwise have been expected to grow.

Summary of Stable Disease 

Since metastatic disease—that is, cancer that has spread to another region of the body—is responsible for at least 80 percent of deaths from cancer, coping with the fear of recurrence or progression of cancer is one of the greatest fears for people living with cancer. Stable disease is, therefore, a reassuring sign for many people, and even if the response to treatment isn't what you had hoped for, stable disease also means that there is still the hope that a new treatment—one that works better—will become available in your lifetime.

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Article Sources

  • Bast, R., Croce, C., Hait, W. et al. Holland-Frei Cancer Medicine. Wiley Blackwell, 2017.