Researchers believe that the side effects of chemotherapy treatment for breast cancer are probably higher than thought.

New research by the Dana-Farber Cancer Institute, in Boston and Harvard Medical School, has found that the side effects of chemotherapy along with related costs are possibly underestimated.

Study author Dr. Michael Hassett says when the rates of side effects commonly associated with chemotherapy were examined they found women experienced more hospitalizations or emergency room visits for these side effects than was previously estimated.

Doctors often prescribe chemotherapy to eliminate residual cancer cells in women who have undergone surgery for breast cancer.

The study was carried out to find out how chemotherapy-related serious adverse effects affected a population of younger women with breast cancer as it is the most common reason why American women receive chemotherapy.

According to the researchers hospitalizations due to chemotherapy side effects are thought to be rare, but only one study has previously been done to measure the side effects of chemotherapy on the general population.

Hassett says they wanted to find out how frequently side effects occurred in the general community, because what happens in the community may be different from what is seen in clinical trials.

To better assess the incidence of side effects, Hassett and his team collected data from a pool of 12,239 women who had been recently diagnosed with breast cancer, all were under the age of 63 and 4,075 of which had received chemotherapy.

The researchers examined hospitalization and emergency room visits in the year following the initial diagnosis for both women who received chemotherapy and those who did not and found that women on chemotherapy were much more likely to visit the emergency room or be hospitalized for any cause than women who had not had chemotherapy; 61 percent compared to 42 percent.

Women who received chemotherapy were found to be more likely to be hospitalized or visit emergency rooms for problems that are typically related to chemotherapy, including fever or infection, low white blood cell or platelet count, nausea, diarrhea, malnutrition or dehydration.

For the women who received chemotherapy this equated to more than $1,200 in additional health-care expenditures related to chemotherapy and more than $17,000 in additional costs for ambulatory care than women who did not receive chemotherapy.

Hassett believes there are a number of possible explanations for these events; clinical trials may not detect all of the side effects that occur and people enrolled in clinical trials may be less likely than those treated in the general community to experience serious side effects of chemotherapy.

Also clinical trials may not have enough power to detect rare side effects.

Hassett says there is also the chance that the study may have overestimated the likelihood of serious side effects of chemotherapy, because hospital bills rather than medical records were used to identify such events.

Other experts say that tracking adverse events is a very difficult task, and the systems used are not imperfect.

They say women should not be deterred by chemotherapy but should ask about how much of a benefit to expect and what types of side effects may be experienced.

Women also need to recognize that such information may be changing more often as new drugs are developed and treatment regimes change.

Hassett hopes as a result of the study, women with breast cancer will understand that deciding whether or not to have chemotherapy must be made on an individual basis, and will talk with their doctors about both the benefits and risks of chemotherapy.

For women with small cancers, he says the benefits may not outweigh the risks, whereas for women with larger or higher-risk cancers, the benefits usually outweigh the risks.

The research was funded by grants from the Agency for Healthcare Research and Quality and the National Institutes of Health.

The study is published in the August 16 issue of the Journal of the National Cancer Institute.