MONDAY, Oct. 15 (HealthDay News) -- Being obese promotes the growth of existing tumors regardless of diet, according to a new animal study that may shed light on why obese cancer patients often have worse outcomes than lean patients.

Previous research has clearly established a link between obesity and cancer risk and shown that obesity is associated with a poorer prognosis, according to Mikhail Kolonin, an associate professor at the Institute of Molecular Medicine at the University of Texas Health Science Center at Houston.

He and his colleagues examined how obesity might promote cancer progression. Their findings were published in the Oct. 15 issue of the journal Cancer Research.

"Our earlier studies led us to hypothesize that fat tissue called white adipose tissue, which is the fat tissue that expands in individuals who are obese, is itself directly involved and that it is not just diet and lifestyle that are important," Kolonin explained in a journal news release.

Their initial results confirmed this theory. They found that tumors grew much faster in obese mice than in lean mice that ate the same diet. The researchers also found that obese mice had far more white adipose tissue cells (adipose stromal cells) than lean mice, which led them to focus on these cells.

The team discovered that cancer triggered adipose stromal cells to move into the blood stream. Once they find their way to tumors, some of these cells developed into fat cells. However, others were incorporated into blood vessels that actually helped provide oxygen and nutrients to tumors, boosting the cancer's growth.

"The fact that these cells are present in tumors is still an emerging concept. We have shown that not only are they present, but they are also functional and affect tumor growth. Identifying the signals that cause these cells to be recruited to tumors and finding ways to block them might provide a new avenue of cancer treatment," Kolonin said.

One cancer expert called the finding "a significant advancement of the understanding of tumor biology." Dr. Daniel Budman, of the Don Monti Division of Oncology at the Monter Cancer Center of North Shore--LIJ Health System in Lake Success, N.Y., added that "obesity has been long recognized as a risk factor for some clinical cancers and may also be an adverse prognostic factor in patients treated for their tumors."

He said the current study "demonstrates that these adverse factors are at least in part a consequence of the white adipose tissue [fat] which leads to increased angiogenesis and tumor growth."

According to Budman, the implications for patients are clear: "reduce obesity before appearance of tumors and after." For scientists, the challenge will be to find agents that might convert cancer-linked "white" fat cells to less harmful "brown" fat, or agents that impede the transfer of adipose cells into tumors, he said.

Health experts note that research involving animals isn't always applicable to humans.

More information

There's more on the obesity-cancer link at the U.S. National Cancer Institute.