Consider it cancer's cloak of invisibility.

Lymphoma tumor cells can shield themselves from chemotherapy and survive through a patient's treatment by hiding out in the thymus, an organ near the heart where the body's immune cells mature, a new animal study suggests. The finding could help explain why cancer patients relapse.

Chemotherapy treatments expose both tumor and normal cells to toxic compounds. In lymphoma, which is a cancer of immune system, cells in the thymus release a host of proteins for protection against the toxic onslaught — thymus cells are important to protect from toxins because they develop into different kinds of blood cells, said study researcher Michael Hemann, an assistant professor of biology at the Massachusetts Institute of Technology.

However, tumor cells in the thymus can hijack these protective proteins to stay alive amid chemotherapy, which could be why cancer patients relapse, Hemann told MyHealthNewsDaily.

"This is clearly an unexpected mechanism by which tumor cells can survive chemotherapy," he said. "It remains to be seen how widespread this mechanism is, but it may, in part, explain why it is so difficult to fully eradicate certain tumors."

In the study, mice with lymphoma were treated with the chemotherapy drug doxorubicin, which is used to fight a wide range of cancers. The researchers found the drug triggered a protective response in the environment surrounding the tumor cells, enabling them to survive the drug's toxicity. A protein called interleukin-6, in particular, supports cell survival.

Although the study was done only in mice with lymphoma, Hemann said the findings may apply to other cancers, too.

"We think other organ systems may function in similar ways," because cells send out survival signals to protect them during times of stress, like during chemotherapy, he said.

The tumor-hiding technique has not been demonstrated in humans. But researchers said there's potential for a drug to be developed that would target the protector proteins that shield the tumor cells. The potential drug could be even more effective used in combination with chemotherapy, Hemann said.

"Effective therapies will involve drugs that kill cancer cells, as well as agents that inhibit survival signaling from the tumor," he said.

Next, Hemann said he and and his colleagues will give mice arthritis drugs, which inhibit the cell-survival protein interleukin-6, in addition to chemotherapy, to see if the combination is more effective in killing tumor cells than chemotherapy alone.

The study was published today (Oct. 29) in the journal Cell.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.