A new study found that women who are overweight or obese tend to have more aggressive breast cancers and lower survival rates.
The researchers suggest that a person's Body Mass Index (BMI, the ratio of a person's weight to the square of their height) may be an effective tool in the
prognosis of certain types of breast cancer.
The study is to be published in the 15th March issue of the journal Clinical Cancer Research and is the work of Dr Massimo Cristofanilli, associate professor of medicine at the Department of Breast Medical Oncology based at The University of Texas MD Anderson Cancer Center, Texas, USA, and colleagues.
In the retrospective study of over 600 women, the researchers found that high BMI women with locally advanced breast cancer (LABC) and inflammatory breast cancer (IBC) had a worse prognosis than women with the same cancers whose BMI was in the healthy range.
"The more obese a patient is, the more aggressive the disease," said Cristofanilli.
"We are learning that the fat tissue may increase inflammation that leads to more aggressive disease," he added.
BMI is calculated by taking a person's weight in kilograms and dividing it by their height in metres, squared. A healthy BMI is one in the range 18.5 to 24.9. Under 18.5 is classed as underweight, and 25.0 to 29.9 is overweight, while over 30 is obese. Thus a person who is 5 feet 8 inches tall (1.72 metres) and weighs 180 pounds (81.7 kilos) has a BMI of 27.4, and would be classed as overweight, whereas someone else of the same height but weighing 30 pounds less has a BMI of 22.8 which is in the healthy range.
In their background information the researchers explain that about 5 per cent of new breast cancer diagnoses in the US every year are of the LABC type, that is breast cancer that has spread to nearby tissue or lymph nodes. IBC, although extremely aggressive, is not so common, and represents between 1 and 2 per cent of breast cancer diagnoses in the US.
Cristofanilli said that before this study few others had found a link between weight gain, obesity and risk of developing breast cancer, and even fewer had looked at the possibility of obesity having any prognostic value.
"This is the first study to highlight the value of BMI at the time of diagnosis as a prognostic indicator in women with aggressive disease and at a high risk of recurrence and at the time of diagnosis in locally advanced disease, including its most aggressive form, inflammatory breast cancer," he said.
Cristofanilli explained they were prompted to do the research because most of their newly-diagnosed inflammatory breast cancer patients were overweight or obese, and IBC was often linked to poor prognosis.
"The idea was to understand the etiological link between the most aggressive forms of breast cancers and, ultimately, with prognosis," he added.
In the study, Cristofanilli and colleagues examined 606 patients, 82 per cent (495) with LABC and 18 per cent (111) with non-metastatic IBC. All the patients were enrolled between 1974 and 2000, and the median follow up was six years for all patients, and 9.9 for the women who were still alive.
In BMI terms, 34 per cent (208) of the women were normal or underweight, 32 per cent (194) were overweight and 34 per cent (204) were obese. Obesity was more frequent among the IBC women (45 per cent of the women with IBC were obese compare with 31 per cent in those who did not have IBC).
The results showed that:
- Median overall survival for all participants was 8.6 years.
- Recurrence-free survival for all participants was 5.8 years.
- Both these figures were significantly worse for overweight and obese compared to healthy and underweight participants.
- For overweight LABC patients, 5-year survival was 58.3 per cent and 10-year survival was 44.1 per cent.
- For obese LABC patients, these figures were 58.6 and 42.4 per cent respectively.
- This compared with 69.3 and 57.3 per cent for normal or underweight LABC patients.
- Among overweight women with IBC, 5-year survival was 45.3 per cent and 10-year survival was 29.1 per cent.
- Among obese IBC women, these figures were 49.3 and 43.7 per cent.
- This compared with 55.1 and 50.9 per cent for healthy and underweight women with IBC.
Cristofanilli said it was important to explore all ways to prevent overall obesity and that:
"These outcomes may have a major impact not only on the incidence of future breast cancer patients, but on their long-term outcome."
He said there should be more research into the link between obesity and hormones, for instance it might explain why inflammatory breast cancer patients are more frequently obese. He said he and his colleagues were going:
"Back to the lab and start looking into those specific factors related to obesity in breast cancer: insulin, estrogen levels and leptin are areas of immediate interest."
While acknowledging how difficult it must be for women having chemotherapy to change their diet, Cristofanilli said it was important for overweight and obese patients diagnosed with breast cancer to do so.
Tamoxifen, a drug commonly used to treat breast cancer, tends to increase BMI during treatment. Cristofanilli said we have become quite good at managing other side effects of chemotherapy such as nausea, and it goes away in a couple of days. But, after this:
"Our patients tend to overeat, which further increases their risk of weight gain. We need to implement lifestyle modifications interventions and develop better methods to follow these patients closely," urged Cristofanilli.
Before BMI is officially recognized as a prognostic tool, he and his colleagues suggest prospective trials and endocrinology studies should be carried out to confirm these results.
However, Cristofanilli urged oncologists treating overweight and obese LABC and IBC patients to monitor them more closely, eg by giving them more frequent physical exams and scans.
"Prognostic value of Body Mass Index (BMI) in Locally Advanced Breast Cancer (LABC)"
Shaheenah Dawood et al.
Clinical Cancer Research 14 (6).
Published early online Mar 15, 2008.
Click here for Clinical Cancer Research.
Sources: Press releases from the University of Texas MD Anderson Cancer Center and American Association for Cancer Research.
Written by: Catharine Paddock, PhD