Cervical Cancer Prevention (PDQ®): Prevention - Health Professional Information [NCI] - Evidence of Benefit
Vaccine Efficacy of the Quadrivalent HPV Vaccine continued...
Cigarette smoking by women is associated with an increased risk for squamous cell carcinoma.[1,19,20] This risk increases with longer duration and intensity of smoking and may be present with exposure to environmental tobacco smoke, being as high as four times that of women who are nonsmokers and are not exposed to environmental smoking. Case-control studies of women infected with HPV have examined the effect of various types and levels of tobacco exposure and found similar results.[20,21]
High parity has long been recognized as a risk factor for cervical cancer, but the relation of parity to HPV infection was uncertain. A meta-analysis of 25 epidemiologic studies, including 16,563 women with cervical cancer and 33,542 women without cervical cancer, showed that the number of full-term pregnancies was associated with increased risk, regardless of age at first pregnancy. This finding was also true if analyses were limited to patients with high-risk HPV infections (relative risk = 4.99 [3.49–7.13] for seven or more pregnancies versus no pregnancies; linear trend test x2 = 30.69; P < .001).
Long-term use of oral contraceptives has also been known to be associated with cervical cancer, but its relation to HPV infection was also uncertain. A pooled analysis of HPV-positive women from the studies described above was undertaken. Compared with women who have never used oral contraceptives, those who have used them for fewer than 5 years did not have an increased risk of cervical cancer (odds ratio [OR] = 0.73; 95% CI, 0.52–1.03). The OR for women who used oral contraceptives for 5 to 9 years was 2.82 (1.46–5.42), and for 10 or more years, the OR was 4.03 (2.09–8.02). A meta-analysis of 24 epidemiological studies confirmed the increased risk associated with oral contraceptives, which is proportionate to the duration of use. Risk decreases after cessation and returns to normal risk levels in 10 years.
Multiple case-control studies show an association between intake of some micronutrients and lower risk of cervical cancer, but results are conflicting and difficult to control for other risk factors. Two randomized trials of oral folate as a chemopreventive agent have shown no protective effect.
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