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Obesity Linked to Larger, More Aggressive Breast Cancers

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A study found a link between obesity and breast cancers that are larger and more advanced at diagnosis. This study adds to earlier evidence linking being overweight to a worse prognosis when breast cancer is diagnosed. Being overweight or obese also increases the risk of being diagnosed with breast cancer. The results were reported at the 2010 American Society of Breast Surgeons meeting.

The researchers looked at the medical records of 1,352 women diagnosed with invasive breast cancer between the 2000 and 2008. The researchers noted the characteristics of each breast cancer that could influence prognosis, such as how the cancer was diagnosed, tumor size, and lymph node involvement.

Each woman's weight was classified by body mass index (BMI). BMI uses weight and height to determine if a person is underweight, normal weight, overweight, or obese:

  • BMI lower than 18.5 is underweight
  • BMI between 18.5 and 24.9 is normal
  • BMI between 25 and 29.9 is overweight
  • BMI 30 or higher is obese

Nearly 350 women (24%) were classified as obese.

The researchers compared the characteristics of the breast cancers in the obese women to the breast cancer characteristics in non-obese women.

Compared to the cancers in the non-obese women, the breast cancers in the obese women were:

  • larger: 2 cm. compared to 1.6 cm., on average
  • likely to be larger than 2 cm. (tumors smaller than 2 cm. are called T1, while larger tumors are T2 or higher): 71% of obese women had T1 tumors compared to 79% of non-obese women
  • more likely to have spread to the lymph nodes: 31% of obese women had cancer in the lymph nodes compared to 25% of non-obese women

Obese women also had worse survival rates compared to non-obese women, but this different wasn't statistically significant, which means it could have been due to chance and not because of the difference in the women's weight.

Breast cancers that could be felt by hand at diagnosis were less likely in obese women compared to non-obese women -- even though the cancers in the obese women were larger. This suggests that obesity could make it harder to find breast cancer early during a doctor's physical exam or by breast self-exam. This might be part of the reason why breast cancers in the obese women were larger and more likely to have spread to the lymph nodes.

This study offers more evidence that maintaining a healthy weight is worth the effort. A healthy weight can improve your overall health, lower your risk of breast and other cancers, and make it more likely that you'll survive if you're diagnosed with breast cancer.

The National Institutes of Health offers an online BMI calculator that allows you to calculate your BMI. If your BMI is high, talk to your doctor about a safe and sensible plan to lose weight. The Centers for Disease Control also has a Healthy Weight resource that offers information on both losing weight and maintaining a healthy weight.

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