Almost half (48 percent) of the 487 participants questioned at a clinic or over the internet admitted using CAM in conjunction with conventional therapy, and two-thirds of these did so without their doctor's knowledge.
The study, conducted by researchers at the University of Pennsylvania, was presented at the weekend at a meeting of the American Society for Therapeutic Radiology and Oncology's 47th Annual Meeting in Denver.
Lead author Neha Vapiwala, MD, said that the study shows a significant lack of communication between patients and their doctors over CAM use.
Her view is that doctors and patients are missing out on the opportunity to collaborate:
"It's important for doctors to know about their patients' CAM use and to understand patients' reasons for using it, so that they can better tailor and optimize treatment regimens and improve patient quality of life during radiation and/or chemotherapy," she said.
Interestingly, 65 percent of patients being treated with chemotherapy alone said they used CAM, compared to 35 percent of those receiving radiation therapy.
Researchers working on previous studies of CAM use have also raised concerns that patients may not be aware of potential interactions between the supplements and herbal products they take and regular drugs.
In a commentary published in last month's Cancer Journal for Clinicians, Gabriella D'Andrea, assistant clinical member of the Memorial Sloan-Kettering Cancer Center's department of medicine, reviewed evidence for and against the use of antioxidants by cancer patients, a course of action believed by some to reduce the toxicity of treatments.
The scientific jury is still out on its efficacy, however, there is some evidence that antioxidants can actually be harmful for patients being treated with chemotherapy or radiotherapy since they may be unable to differentiate between normal cells and cancer cells. This may mean that treatment is less effective.
D'Andrea advised that, until contrasting evidence from extensive human studies is available, patients should be advised against taking antioxidants during cytotoxic therapy.
"The harmful effects of antioxidants might be important even if they were small; a reduction of only a few percentage points in the efficacy of chemotherapy might lead to hundreds or thousands of deaths every year," she wrote.
Moreover, a study published in the April issue of Breast Cancer Research and Treatment found that black cohosh, a herbal with a long history of use to alleviate menopause symptoms and used by some breast cancer patients for the menopause-like side effects of cancer therapies, may interfere with some drugs.
Black cohosh was seen to increase cytotoxicity (cell killing) by two of the drugs, doxorubicin and docetaxel. It decreased the cytotoxicity of cisplatin.
No change in effect was seen in a fourth drug, 4-hydroperoxycyclophosphamide (4-HC), nor in radiation therapy.