Ask an Expert: Why does cancer come back?

Q: “If lung cancer is caught in the early stage and removed surgically, how does it come back? My surgeon said that he removed it all and there was no cancer in the nodes — but now it’s back. Why?”

Answer from Rachel E. Sanborn, M.D., and John R. Handy, Jr., M.D., medical co-directors of the Providence Thoracic Oncology Program.

There are two different ways that cancer might return in a person who has had a lung tumor removed. The first possibility is that the original tumor had already spread microscopic cancer cells to another part of the lung or the body, before the tumor was removed. The second possibility is that a new cancer developed, independent of the previous cancer.

The first possibility is the most common explanation for cancer that returns. When a small tumor is found in the earliest stage, as yours was, it has a much smaller chance of coming back than a tumor found in a later stage. However, there is still about a 20 to 30 percent chance that the cancer may show up again.

This doesn’t mean that the surgeon left part of the tumor behind, or that the same tumor grew back. After a tumor is removed, surgeons check to make sure they have left a “negative margin” of healthy tissue all the way around the tumor. If no cancerous tissue can be seen growing through this margin, they can say that they have successfully removed all detectable cancer from the area.

The trouble is that not all cancer may be detectable. The smallest tumor we can detect with today’s imaging technologies is about 1 cm, or half an inch, in size. At that size, a tumor already may encompass more than a billion cells. If the original tumor had spread a tiny seed containing just a few thousand cells to another part of the lung, or to the lymph nodes, or to a different part of the body, it could hide and grow silently for months or years until it became large enough to cause symptoms or to be detected in follow-up screening.

The second possibility is that the first cancer didn’t actually come back, but that a new cancer formed. This is less common, but it does happen — whatever caused your body to develop one lung cancer also puts you at increased risk of other cancers. People who have had lung cancer have about a 2 percent chance per year of forming a second cancer, either of the lung or of other organs.

These possibilities are the source of some of the worst fears and frustrations for people who have lung cancer. Even if a surgeon successfully removes all of your detectable cancer, there is no way to guarantee that it won’t return, or that a second cancer will never form.

Wouldn’t chemotherapy kill any cancer cells left behind?
Although chemotherapy is used for later-stage lung cancers, the current standard of care for most people with Stage I lung cancer is not to follow surgery with chemotherapy.

Based on the best evidence today, we know that chemotherapy can help prolong life for people with larger tumors and later-stage lung cancer that has spread to the lymph nodes or to other parts of the body. However, for people with the smallest tumors and no lymph node involvement (stage 1A), there is no evidence that adding chemotherapy can help; to the contrary, for these people, there is concern that the chemotherapy itself appears to increase the risk of causing harm and even death. For people with slightly larger tumors (stage 1B), one trial did seem to suggest, initially, that chemotherapy might extend survival, but after following the data for a longer period of time, no benefit was found.

Research continues
Scientists at Providence Cancer Center, as well as other research facilities across the country, are continuing to explore ways to adjust chemotherapy to achieve a benefit for people with small tumors, and ways to predict which people may be more or less likely to have their cancer come back. Improvements in the tools and techniques available for detecting cancer and its spread, including potential blood tests for cancer detection, also are being studied around the country.

At Providence Cancer Center, other related avenues of investigation include: 
  • Studies to identify molecular markers on small tumors that may help determine whether or not chemotherapy will be helpful after surgery 
  • Analyses of the genetic makeup of tumors to determine whether a treatment can be tailored to the tumor to improve a patient’s outcome
  • Clinical trials of new, limited surgical techniques for removing smaller tumors from people who may be unable to tolerate larger surgeries, due to higher-risk or more severe lung disease
So, where do you go from here?
There are multiple treatments that have been proven to prolong life and to keep quality of life good for people whose lung cancer comes back. The best treatment for you will depend on the type of cancer you have, your general health, and your personal preferences. Talk things over with a medical oncologist, and consider a referral to a radiation oncologist or other subspecialists to learn all you can about your options for treatment or clinical trials. Then weigh the risks and benefits of each carefully so you can make a choice that you feel comfortable with.

March 2009

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