Tumor growth: Sometimes it's a good thing

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“When you get sick, the lymph nodes in your neck may swell as your body amps up its production of white blood cells to fight the infection. The swelling is usually temporary, and once the threat has passed and the infection heals, the lymph nodes return to their normal, bean-shaped size. In a similar way, when an immunotherapy drug is used to treat cancer, it stimulates the production of immune cells to locate and destroy cancer cells, which may cause the tumor to temporarily grow. That may be confusing to doctors and patients who don’t understand that it’s not a sign of disease progression, but, instead, a symptom of what researchers call pseudoprogression—tumor growth from the treatment rather than from the disease itself.

Pseudoprogression is a not-uncommon side effect of immunotherapy that's still being studied to be better understood. In the past, the popular belief was that the tumor was getting bigger and treatment should be stopped. Now we know that it's actually a sign that the immunotherapy may be working,” Pamela Crilley, DO, Department of Medical Oncology Chair at Cancer Treatment Centers of America® (CTCA)

Most of the time, oncologists discover evidence of pseudoprogression during follow-up tests used to determine the cancer’s response to treatment. “Immunotherapy drugs cause the tumor to flare up initially and get bigger, but that’s only temporary,” says Ashish Sangal, MD, Medical Director of the Lung Cancer Center and Medical Oncologist at our hospital in Phoenix. “So anything that looks bigger in the first three to six months after treatment doesn’t mean it’s a progression.”

For that reason, multiple follow-up tests may be required for patients undergoing immunotherapy treatment. “Immunotherapy may take a longer time to determine results than other therapies,” Dr. Crilley says. That’s why it’s important to be patient when evaluating immunotherapy’s effect. “Patients and physicians are coming to understand that, sometimes, you have to do more than one or two evaluations to really be sure of what’s happening,” she says.

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