The epidemiology of cervical neoplasia

Abstract

Controversial topics in the epidemiology of cervical neoplasia are reviewed, in the light of data from studies conducted in Italy and indications from the literature. The downward trends registered over the last three decades in mortality from cervical cancer seem to be levelling off in the younger age groups (below age 45). This may be partly due to changes in sexual habits in younger women, but is certainly attributable to deficiencies in cervical screening. Pap smear, in fact, strongly reduces the risk of cervical neoplasia, the protection (as suggested by data from a case control study), being long lasting (over five years and perhaps around 10-15 years) for invasive cancers. The results of the same case-control study indicate that, although women with pre-invasive and invasive conditions seem to share several unspecific indicators of sexual habits (i.e., total number of partners and age at first intercourse), they appear to differ with regard to clinical history of specific venereal disease. In fact, genital warts, herpes genitalis and trichomoniasis were more frequent in cases of intraepithelial neoplasia, but not of invasive cancer. The implications of these findings, and of other controversial points in the epidemiology of cervical neoplasia, such as oral contraceptives, cigarette smoking and diet, are discussed with regard to indications from other disciplines (chiefly molecular hybridization and stochastic models of carcinogenesis).

PIP: Data from northern Italy are interpreted, along with indications from the literature, to examine the role of risk factors in development of invasive and preinvasive cervical cancer. This case-control data included 183 cases of histologically confirmed cervical neoplasia in women aged 19-71. Mortality has fallen since the 1950s, starting with younger age groups, but since the 1970s, this trend has flattened out, again, starting with younger age groups. Probably changes in life-style as well as less rigorous Pap smear testing are responsible. This study found that risk of moderate dysplasia is a function of time since last smear, but that of invasive cancer depends on the number of smears, suggesting that squamous carcinoma evolves from dysplastic lesions. Both pre-invasive and invasive cancer were positively related to number of sexual partners and age at 1st intercourse. Intraepithelial neoplasia was strongly associated with Condylomata acuminata (genital warts), and trichomoniasis, and (not significantly) with Herpes genitalis and salpingitis. Invasive cancer was not related to any venereal diseases. The risk of intraepithelial neoplasia was elevated within 20 years after starting smoking, but did not increase afterward. In contrast, the risk of cervical cancer was not increased for the first 20 years of smoking, but increased steadily thereafter, to 3-fold after 40 years of smoking. Beta-carotene intake (reflected by vegetable consumption) had a powerful negative association with invasive cervical cancer. No such relationship was apparent with retinol (preformed vitamin A, indicated by dairy and meat consumption).