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Size matters for obese cancer patients' drug dose, doctors say

It doesn’t happen often, but sometimes Dr. Jennifer Griggs’ hand trembles a bit when she prescribes “enormous” doses of chemotherapy drugs for obese breast cancer patients.

Those powerful drugs kill not only cancer cells but healthy cells as well. And that makes some doctors nervous, so they order chemotherapy doses based on patients’ ideal weight, not their actual weight.

But Griggs knows that such hesitation carries a high price: Up to 40 percent of obese cancer patients don’t get large enough chemotherapy doses, jeopardizing treatment of individual patients -- and the overall public health.

Now, Griggs and her co-authors, writing in the latest issue of the Journal of Clinical Oncology, have published new guidelines aimed at making sure even the heaviest cancer patients get the full treatment they need.

“It looks like we could save up to 6,000 lives in breast cancer a year,” Griggs says, by giving obese patients the right-sized dose.

The guidelines should help resolve confusion among cancer doctors over the correct doses for patients who weigh in at 250, 300, even 400 pounds.

“I get a lot of emails from people who … want to fully dose, and their colleagues are telling them they can’t,” says Griggs, a University of Michigan breast cancer specialist.

The confusion over how much chemo to give obese patients stems in part from the caps research trials used to put on doses, Griggs and her coauthors write.

Take the drug docetaxel, or Taxotere, used to treat breast and lung cancers. The traditional capped dose is 150 milligrams. But for a 400-pound patient, the size-based dose would be 212 milligrams, a significant difference, says Judith Smith, director of pharmacology research at the University of Texas M.D. Anderson Cancer Center in Houston.

Even at that world-renowned institution, some doctors insist on using outdated caps, says Smith, of the department of gynecologic oncology and reproductive medicine.

“The physicians fight me on it,” says Smith, who was not involved in writing the new guidelines. Still, she says, “I don’t fight that battle on a daily basis anymore.”

The authors of the new guidelines acknowledge a scarcity of studies that randomly assigned obese patients to capped doses or size-based doses of chemotherapy drugs.

But, they write, research suggests that obese cancer patients actually do better, not worse, when treated with doses commensurate with their size. They don’t experience any more toxicity with weight-appropriate doses than do lean patients, and they are more likely to be cured than those who are under-dosed.

“You’re not going to harm your patient if you give them the full dose,” Griggs’ co-chair Dr. Gary Lyman, a professor of medicine at the Duke Cancer Institute, tells msnbc.com. “In fact, just the opposite.”

Under-dosing is probably a “significant” contributor to the higher cancer death rates among overweight and obese patients, Lyman says.

Size-based dosing might most benefit breast cancer patients who are black and/or poor, the authors write. No matter what they weigh, breast cancer patients in those groups are more likely to receive reduced doses of chemotherapy, and their higher rates of obesity only compound the problem.

Correct dosing would be a boon even amid an ongoing shortage of cancer drugs, says Lyman, who calls the situation "a travesty." Appropriate dosing of obese patients should have little or not impact on the shortage situation. In most cases, Lyman says, fully dosing obese patients simply means using all of the vial of a drug instead of throwing away part of it.

There are exceptions to the recommendation of full dosing of chemotherapy drugs for obese patients, according to the guidelines. Fixed doses, prescribed independent of a patient’s weight, are justified for a few, such as carboplatin and bleomycin, because of concerns about nerve tissue damage.

The guidelines note that costs, even insurance co-pays, could be higher with larger doses, although, Griggs says, many chemotherapy drugs are off-patent and relatively inexpensive.

And, Lyman says, the cost of treating recurrent cancer or providing palliative care after the disease has spread “probably far outweighs giving the full dose of chemotherapy.”

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