Antibiotics and Breast Cancer-What's the Meaning of This?
JAMA, Vol. 291 No.7, February 18, 2004' pp. 880-881
Roberta B. Ness, MD, MPH; Jane A. Cauley, DrPH
THESE AUTHORS NOTE IN THEIR EDITORIAL:
"Breast cancer is the most frequent cancer diagnosed among women in the United States."
"Established risk factors include age, family history, reduced parity, earlier age at menarche, alcohol use, postmenopausal adiposity, and hormone therapy."
"In this issue of THE JOURNAL, Velicer and colleagues report another potential risk factor: the use of prescribed antibiotics."
Among 2266 women with breast cancer, as compared with 7953 controls, the use of antibiotics was more common;
"The risk of breast cancer was greater with longer duration of antibiotic use and was consistent across antibiotic classes."
"This observation is potentially worrisome in that antibiotic exposure is common and sometimes nonessential. Thus, if real, the risk of breast cancer attributable to the use of antibiotics could be large and partially preventable. "
Among patients with the highest use of antibiotics, risk of breast cancer was increased regardless of the indication: acne, rosacea, or respiratory tract infections.
"Computerized pharmacy records were used to validate antibiotic prescriptions and adjustment was made for a number of potentially confounding factors."
Velicer et al raise 2 mechanistic possibilities:
1) Antibiotics may reduce the capacity of intestinal microflora to metabolize phytochemicals that might protect against carcinogenesis;
2) Tetracyclines stimulate prostaglandin E2, implicating an overexpression of cyclooxygenase 2, the enzyme that synthesizes prostaglandin E2 and that has been associated with mammary carcinogenesis.
Compelling evidence links inflammation and breast cancer.
"Further support for the idea that inflammation plays a role in breast carcinogenesis comes from an evolving understanding that immune mechanisms may contribute to a variety of tumor-promoting actions when those mechanisms are not in balance." [O'Byrne KJ, Dalgleish AG. Chronic immune activation and inflammation as the ca of malignancy. BrJ Cancer. 2001;85:473-483].
"Chronic inflammation can produce DNA damage via reactive oxygen species." "This study raises the possibility that long-term use of antibiotics may have ha consequences, especially for patients for whom other therapeutic options are available. "
KEY POINTS FROM DAN MURPHY
1) Breast cancer is the most frequent diagnosed cancer among US women.
2) A potential risk factor for breast cancer is the use of prescribed antibiotics.
3) The risk of breast cancer is greater with longer duration of antibiotic use a seen in all classes of antibiotics.
4) The risk of breast cancer attributable to the use of antibiotics could be large.
5) Antibiotics reduce the capacity of intestinal microflora to metabolize phytochemicals that protect against cancer.
6) Tetracyclines stimulate prostaglandin E2, implicating an over-expression of cyclooxygenase 2. Remember that prostaglandin is derived from the omega-6 acid arachidonic acid.
7) Compelling evidence links inflammation and breast cancer.
8) Chronic inflammation can produce DNA damage from free radicals.