Obesity has become a well-known risk factor for cancer, and with this in mind, the findings of a new study may come as a surprise; for patients with kidney cancer, being overweight or obese appeared to significantly increase their chances of survival.
Senior and corresponding author Dr. Toni K. Choueiri, director of the Lank Center for Genitourinary Oncology at the Dana-Farber Cancer Institute in Boston, MA, and colleagues report their results in the Journal of Clinical Oncology.
According to the American Cancer Society, obesity can trigger changes in hormones that lead to renal cell carcinoma (RCC) - the most common form of kidney cancer, accounting for around 9 in 10 of all cases.
Being overweight or obese following a cancer diagnosis has also been associated with poorer survival, though some previous studies have indicated that this may not be the case with RCC.
For example, a 2013 study of more than 2,100 patients with RCC found that those who were overweight or obese had reduced disease progression and better survival than those of a normal weight.
Choueiri and colleagues decided to further investigate the link between weight and kidney cancer survival by analyzing data from four medical databases, including The Cancer Genome Atlas (TGCA) project and the International Metastatic Renal Cell Carcinoma Database Consortium (IMDC).
Survival increased by 9 months for overweight kidney cancer patients
From the IMDC dataset, the team gathered information - including weight, height, and treatment outcomes - for 1,975 patients who had received targeted therapies for RCC.
- Around 62,700 people in the United States will be diagnosed with kidney cancer this year
- Approximately 14,240 Americans will die from the disease
- Kidney cancer is most common among people aged 45 and older.
Compared with patients who had a low BMI, those with a high BMI - overweight or obese - lived much longer; patients with a low BMI lived an average of 17.1 months, compared with 25.6 months for those with a high BMI.
This association was validated in an external cohort of 4,657 treated for kidney cancer between 2003-2013, the researchers report.
Data from TGCA provided clinical and genomic information on 324 patients with kidney cancer, and another database held information on tissue samples for 146 kidney cancer patients.
The team used this information to determine whether there were any molecular differences between kidney cancer patients with a high or low BMI that might explain why the latter has better survival.
While TGCA data did not provide any clues, the tissue sample database revealed some variations in gene expression; the researchers found that patients with a high BMI showed reduced expression of a gene called fatty acid synthase (FASN), compared with those with a normal BMI.
FASN could be a target for kidney cancer treatment
FASN is known to play an important role in cells' production of fatty acids - a process known as lipogenesis; overexpression of this gene has been identified in various forms of cancer, and it has been linked to poor outcomes in cancer patients, including those with kidney cancer.
Based on their findings, the researchers speculate that reduced expression of FASN in kidney cancer patients may explain why those who are overweight or obese live longer than patients who are a normal weight or underweight.
What is more, they say the results suggest it may be possible to block FASN to improve outcomes for patients with kidney cancer; FASN inhibitors are already in development and have been hailed as a promising cancer treatment.
"We plan to test FASN inhibitors in an animal model as a possible therapy for kidney cancer," says Choueiri.