Obese Women Receive Reduced Doses of Breast Cancer Chemotherapy

Reviewed study: "Obese Women Receive Reduced Doses of Breast Cancer Chemotherapy" by J. Griggs et al., Archives of Internal Medicine, June 13, 2005

Is this for me? If chemotherapy is part of your breast cancer treatment, you might want to read this article, particularly if you are overweight.

Background and importance of the study: Women who are overweight or obese have a higher risk of their breast cancer coming back. Heavier women also have lower survival rates than women who weigh less. The lower survival rates in heavy women may be because they have higher estrogen levels. Extra fat cells make extra estrogen. Or they may not do as well because they are treated differently.

Women whose breast cancer has not spread (metastasized) receive chemotherapy to reduce the risk of cancer coming back. Chemotherapy doses generally are based on the body surface area (BSA), which is calculated using height and weight. This means that a bigger person gets a bigger dose of each chemotherapy drug.

But some doctors worry about the possible danger of giving the very high doses that are calculated using an overweight or obese patient's full weight. So these doctors may decide to decrease the dose of chemotherapy. Several studies have shown that overweight and obese women are more likely to be given lower doses for their size than lean women. Other studies have shown that these dose reductions are not necessary. In fact, they reduce the effectiveness of the chemotherapy.

In the study reviewed here, researchers from the University of Rochester wanted to know:

• how many women got doses of chemotherapy that were lower than the doses to be expected if based on actual body weight,
• whether heavy women who did get full doses (based on actual weight) were more likely to be admitted to the hospital to treat common chemotherapy side effects, and
• whether the women's age, presence of other medical problems (such as diabetes), or the year of treatment were related to the reduced doses of chemotherapy.

Study design: The researchers looked at the treatment records of 9,762 women who received chemotherapy for breast cancer at 901 centers between 1990 and 2001. The treatment centers included big and small medical practices from all over the United States.

The researchers looked at the height and weight of each woman and calculated the dose of chemotherapy that would be expected. Then they looked at the dose of chemotherapy actually given to each woman for her first treatment and for the entire course of chemotherapy. If the actual dose was less than 90% of the expected dose, the woman was considered to have had a dose reduction. Dose reductions for the first chemotherapy treatment were looked at separately from dose reductions that happened after the first treatment.

For each woman, the researchers also looked at:

• other medical problems,
• age,
• year of treatment, and
• whether or not the woman was hospitalized because of fever and low white cell counts (also called "febrile neutropenia").

Results: The researchers found that most women received doses of chemotherapy that were based on their full weight. Heavier patients were more likely to receive reduced doses, however. The heavier the woman, the greater the likelihood she received a reduced dose:

• 9% of normal-weight women,
• 11% of overweight women,
• 20% of obese women, and
• 37% of severely obese women received reduced doses.

The researchers also found that women were more likely to get reduced doses if they

• had other medical problems,
• were older than 60, or
• were treated earlier in the study period.

The association between weight category and reduced doses didn't change when the researchers considered the other factors listed above. In other words, an obese woman or a severely obese woman was more likely to receive a reduced dose of chemotherapy even if she had no other medical problems, was young, and was treated in the last year of the study period.

Receiving a full weight-based dose of chemotherapy didn't cause more hospital admissions for the most common side effect of chemotherapy, fever and low white cell counts. In fact, severely obese women who were given full doses had a LOWER risk of this happening than lean women who were given full doses.

Conclusions: The researchers concluded that reduced doses of chemotherapy are commonly administered to obese women. They also concluded that full doses, even in the severely obese, are not associated with a greater risk of serious side effects.

The finding that heavy women have fewer serious side effects even when given full chemotherapy doses is consistent with other studies. Larger studies also have shown that long-term side effects are not more common when heavy women have full doses of chemotherapy. Most important, other research has shown that such dose reductions are associated with a greater risk of the cancer coming back in other parts of the body.

• Research News on Chemotherapy (40 Articles)