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SMOKING DOES NOT CAUSE BREAST CANCER

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Bibliography on studies - The untold evidence

A summary of the largest studies, based on the criteria of: Cigarette smoking and the risk of breast cancer. JR Palmer, L Rosenberg. Epidemiologic Reviews 1993;15(1):145-156. Their review concludes that smoking neither increases nor decreases risk. And, there is no suggestion of a dose/response, which is necessary to infer causation.

"For purposes of this review, we excluded studies of prevalent disease... We also excluded studies with insufficient detail (e.g., lacking confidence intervals, number of exposed cases, and definition of the reference category); all of these studies had fewer than 300 cases. We further excluded case- control studies in which patients with smoking-related diagnoses were included in the control series," to eliminate biases which falsely lower risks.

 A dual study by Meara (1989) confirmed that screening studies tended to show risks above 1.0, and that hospital studies tended to show risks below 1.0. When one screening study (Schechter 1985) was updated in 1989, the originally reported risks of up to 3.6 had dropped to 0.9 to 1.2, just by the addition of new cases. Needless to say, the media ballyhooed the early claims, but not the later ones.

 "In five studies with healthy controls, the participation rates were less than 80 percent, low enough to admit the possibility that some or all of the modest increases in risk observed in smokers were due to bias." The authors of one (Chu et al) admit that "Telephone surveys have indicated that refusal rates in research studies are higher among persons with less education and lower income," who are more likely to smoke, which creates a deficiency of smokers among controls. They estimated a maximum bias of 0.1 in their study, which would make all their results non significant.

 Contrary to propaganda, "the many epidemiologic studies of endogenous estrogens have not produced a consistent explanation of how the estrogen environment affects risk....The relation between cigarette smoking and endogenous estrogens is also unclear...hormone studies in smokers and non- smokers have failed to demonstrate a consistent association." In other words, "a strong link between estrogen activity and cigarette smoking, or between estrogen levels and breast cancer, has not been demonstrated." The originator of the myth that smokers are estrogen-deficient was one B MacMahon (1982), and all of the 8 breast cancer studies he was involved in were rejected under the reviewers' control bias criteria.

STUDIES WITH OVER 1000 CASES:

Hiatt RA, Fireman BH. Smoking, menopause, and breast cancer. JNCI 1986;76(5): 833-836. 1363 cases. <1p 0.95 (0.80-1.11), 1-2p 1.22 (1.05-1.43), 2+p 1.19 (0.88-1.60). Current smokers 1.08 (0.89-1.31).

Ewertz M. Smoking and breast cancer risk in Denmark. Cancer Causes Control1990;1:31-37. 1480 cases. 1-4c 0.93 (0.69-1.25); 5-9c 1.05 (0.81-1.35); 10-14c 1.02 (0.82-1.28); 15-19c 1.01 (0.76-1.35); 20+c 0.75 (0.56-1.00). Current smokers 0.96 (0.74-1.25).

Brinton LA. Cigarette smoking and breast cancer. Am J Epidemiol 1986;123:614-622. (ACS/NCI). 1547 cases. <10c 1.15 (0.9-1.4); 10-19c 1.41 (1.1-1.8); 20-29c 1.15 (0.9-1.4); 30-39c 1.24 (0.9-1.8); 40+c 1.15 (0.8-1.6). Current smokers 1.18 (0.9-1.4).

Field NA, Baptiste MS et al. Cigarette smoking and breast cancer. Int J Epidemiol 1992;21(5):842-848. 1617 cases; <1/2p 0.88 (0.73-1.06), 1/2-1p1.17 (1.00-1.37), 1 1/2p 0.87 (0.66-1.14), 2p 0.98 (0.70-1.39), >2p 1.16 (0.68-1.96) adjusted. Ever smokers 1.03 (0.90-1.19).

Baron JA, Byers T et al. Cigarette smoking in women with cancers of the breast and reproductive organs. JNCI 1986;77(3):677-680. 1741 cases. 1-14py 0.91(0.75-1.10), 15+py 0.93 (0.76-1.13).

London SJ, Colditz GA et al. Prospective study of smoking and the risk of breast cancer. JNCI 1989;81(21):1625-1631. 1788 cases. 1-14 c/d 0.98 (0.82-1.17), 15-24 0.99 (0.85-1.15), 25+ 1.02 (0.86-1.22), multivariate.

Palmer JR, Rosenberg L et al. Breast cancer and cigarette smoking: a hypothesis. Am J Epidemiol 1991;134(1):1-9. 1955 cases. <25c 1.2 (0.8-1.9), 25-34 1.2 (0.9-1.8), 35+ 1.1 (0.7-1.8). Current smokers 1.3 (1.1-1.6).

Rosenberg L, Schwingl PJ et al. Breast cancer and cigarette smoking. NEJM 1984;310(2):92-94. 2160 cases. 1-14c 1.3 (0.9-1.8), 15-24c 1.0 (0.8-1.4), 25+c 1.1 (0.8-1.6). Current smokers 1.1 (0.9-1.3).

Chu SY, Stroup NE et al. Cigarette smoking and the risk of breast cancer. Am J Epidemiol 1990; 131(2):244-253. 4720 cases. <15c 1.1 (1.0-1.3); 15-24c 1.2 (1.0-1.3); 25+ 1.2 (1.1-1.4). Current smokers 1.2 (1.1-1.3).

Stockwell HG. Cigarette smoking and the risk of female reproductive cancer. Am J Obstet Gynecol 1987;157:35-40. 5246 cases. <20c 1.3 (1.1-1.5), 20-40c 1.2 (1.0-1.4), >40c 1.2 (0.8-1.6), age adj. EXCLUDED BY PALMER AND ROSENBERG:

Vessey M, Baron J et al. Final report of an epidemiological study. Br J Cancer 1983;47:455-462. 1176 cases. Heavy smokers 0.54 crude, 0.67 adj. [Baron 1984: 1-14 c/d 0.77]. Excluded for smoking related disease controls.

Centers for Disease Control. Long-term oral contraceptive use and the risk of breast cancer. JAMA 1983;249:1591-1595. In: Baron JA. Smoking and estrogen-related disease. Am J Epidemiol 1984;119(1):9-22. 1473 cases. Data from CDC author: ever smoker 0.99.

Garfinkel L. Cancer mortality in non-smokers: prospective study by the American Cancer Society. JNCI 1980;65:1169-1173. 3096 deaths. [Baron 1984:smokers ÷1.0. Excluded for inclusion of prevalent cases.]