Here's how obesity can affect cancer development

Adipose tissue, or fat, may influence the development of cancer in diverse ways, depending on the type of fat and the location in the body, say researchers.

"Obesity is increasing dramatically worldwide, and is now also recognised as one of the major risk factors for cancer, with 16 different types of cancer linked to obesity," said Cornelia Ulrich from the University of Utah in Salt Lake City, US.

"We urgently need to identify the specific mechanisms that link obesity to cancer," Ulrich said.

Previous research has shown several ways that fat contributes to carcinogenesis.

For example, obesity increases the risk of inflammation, which has long been associated with cancer.

Also, obesity is believed to affect cancer cell metabolism and immune clearance, all of which can contribute to the growth and spread of tumours, she said.

The relationship between fat and carcinogenesis also depends upon "crosstalk," or the ways cells react when the same signal is shared by more than one signalling pathway in two different cell types, Ulrich explained.

Identifying ways to interrupt the crosstalk could help researchers identify new cancer prevention strategies.

In the study, published in the journal Cancer Prevention Research, Ulrich and colleagues conducted a literature review covering publications from January 1946 to March 2017, seeking studies that explored crosstalk between adipose tissues and carcinomas.

They ultimately found 20 primary research publications that specifically addressed the topic, illustrating the novelty of this work.

The review provided a deeper look into the mechanisms of carcinogenesis, Ulrich said.

For example, several studies showed that adipose stromal cells have the power to infiltrate cancer lesions and promote the growth of tumours.

These cells were found in greater number in obese prostate cancer and obese breast cancer patients, studies showed.

The review also showed how some types of fat are more "metabolically active", secreting more substances that lead to the growth of cancer, Ulrich said.

There are three different types of fat: white, brown, and beige -- and each acts differently and is present in different amounts depending on where the fat is located.

For example, the review noted, white adipose tissue has been associated with inflammation, and in breast cancer patients, has been associated with worse prognosis.

The study supports the importance of maintaining a healthy body weight. Because fat exists both under the skin and deeper inside the body, even slender people may have excess fat surrounding internal organs.

Healthy diets and exercise that includes strength training to build lean muscle mass can help fight the development of excess fat, Ulrich said.