After having surgery for pancreatic cancer, obese people with a BMI of 35 or more seem to be the most likely to have poorer outcomes such as cancer that has spread to the lymph nodes, lower rates of survival and higher rates of cancer recurrence.

The study was the work of Dr Jason B Fleming, from the University of Texas MD Anderson Cancer Center in Houston, and colleagues and is published online in the March issue of the Archives of Surgery a Journal of the American Medical Association.

A person is classed as obese if their Body Mass Index (BMI, weight in kilos divided by the square of height in metres, kg/m2) is 30 or more. The "ideal" or normal range is 18.5 to 25: being outside of this range is linked to various health problems for underweight, overweight and obese people.

Rates of obesity have risen sharply in the US in the last 20 years, wrote the authors in their background information.

"In many obesity-related diseases and malignant neoplasms [cancerous tumors], an increased prevalence of pancreatic cancer has been reported in numerous epidemiologic and cohort studies focusing on obese patients," they wrote.

"Further, obesity has been associated with decreased survival in patients with pancreatic adenocarcinoma, although the mechanism remains unknown," they added.

For this study they wanted to examine the link between obesity, as measured by BMI, and medical outcomes and survival of patients who have had their pancreas removed to treat pancreatic adenocarcinoma.

The study looked at the results retrospectively (that is they found data relating to surgeries that had already taken place as opposed to setting up the study beforehand). The researchers looked at records from 285 consecutive patients whose BMI data was available and who had undergone "potentially curative pancreas resection to treat adenocarcinoma".

All the patients had attended a referral center with a dedicated multidisciplinary pancreas cancer program between 1 January 1999 and 31 October 2006.

In their statistical analysis the researchers looked for links between BMI and other prognostic information and the incidence of lymph nodes metastasis (how far the cancer had spread if it had), and survival rates.

The results showed that:

* Over the 16 month midpoint of the study (median follow up), 152 patients died (53 per cent).

* Patients whose BMI was over 35 survived a median of 13.2 months compared with 27.4 months for those whose BMI was under 23.

* At the last follow up, 15 of 20 patients (75 per cent) whose BMI was over 35 had died, compared with 137 of 265 patients (52 per cent) whose BMI was 35 or less.

* Cancer spreading to the lymph nodes was 12 times more likely in obese patients with BMI over 35 than in patients whose BMI was 35 and under.

* Disease-free and overall survival was also lower in patients whose BMI was above 35, and the risk of cancer recurrence and death after having their pancreas removed was nearly twice that of patients whose BMI was 35 and under.

The researchers concluded that:

"Obese patients with a BMI of more than 35 are more likely to have node-positive pancreatic cancer and decreased survival after surgical resection."

"Data suggest that the negative influence of BMI of more than 35 on cancer-related end points is unrelated to the potential complexity of performing major oncologic surgery in obese patients," they added.

Other studies have shown links between BMI over 35 and increased risk of death from pancreatic cancer, noted the authors, who wrote that:

"Our findings extend these observations to those patients who undergo surgery to treat pancreatic cancer and suggest that obesity is a host factor affecting tumor biology independent of the difficulties (patient- and treatment-related) involved in delivering oncologic care in obese patients."

"Future investigations should include a search for systemic or tumor biomarkers in this group of patients that could provide additional insight," they added.