Tumor growth: Sometimes that’s a good thing

When you get sick, the lymph nodes in your neck may swell as your body increases production of white blood cells to fight infection. The swelling is usually temporary, and once the threat is gone and the infection is treated, the lymph nodes return to their normal bean-shaped size. Similarly, when an immunotherapy drug is used to treat cancer, it stimulates the production of immune cells to locate and destroy cancer cells, which can temporarily cause a tumor to grow. This can be confusing to clinicians and patients who do not understand that it is not a sign of disease progression, but rather a symptom of what researchers call pseudo-evolution — tumor growth from treatment rather than from the disease itself.

“False progression is a common side effect of immunotherapy that is still being studied to better understand. In the past, the common belief was that a tumor was getting bigger and treatment should be stopped. Pamela Creely, chief of medical oncology at Cancer Centers of America, said: We now know it’s actually a sign that immunotherapy may be working.” (CTCA) ^®

Most of the time, oncologists discover evidence of false progression during follow-up tests that are used to determine the cancer’s response to treatment. “Immunotherapy drugs cause the tumor to swell and enlarge at first, but this is only temporary,” says Ashish Sangal, MD, medical director of the Lung Cancer Center and an oncologist at our hospital in Phoenix. “So anything that appears larger in the first three to six months after treatment does not mean it has progressed.”

For this reason, multiple follow-up tests may be required for patients undergoing immunotherapy. “Immunotherapy can take longer to establish results than other treatments,” Dr. Creeley says. That’s why it’s important to be patient when evaluating the effect of immunotherapy. “Patients and clinicians are beginning to realize that sometimes it takes more than one or two evaluations to really be sure of what’s going on,” he says.

Since 2000, oncologists have relied heavily on a system called the Standard Tumor Response Evaluation Criteria (RECIST) to measure a cancer’s response to a particular treatment and guide treatment decisions. But a new evaluation standard, called the immune system-related response (irRC) criteria, explains the phenomenon of false progression and is being used in many clinical trials of immunotherapy drugs. “It’s important to know that this is still evolving, but we are working to better understand response patterns,” Dr. Creeley says.

Some studies have found that false progression indicates a better outcome, although more studies are needed. As researchers work to learn more about the causes of pseudo-progression and what it could mean for patients who suffer from it, communication between clinicians and patients is critical. “As immunotherapy is still very new, more and more information is being announced,” Dr. Creeley says. “Oncologists should educate their patients about what is known at the time, and when new information emerges, it should be communicated to them as quickly as possible.”