Risk factors for invasive cervical cancer and reduction of risk by 'Pap' smears in Thai women.

A case-control study of invasive cervical cancer was conducted in Siriraj Hospital, Thailand, as part of a WHO-sponsored collaborative study of neoplasia and steroid contraceptives. Data from 189 histologically confirmed cases and 1023 randomly selected hospitalized controls who were recruited from October 1979 through March 1983 were analysed to identify risk factors for cervical cancer in Thai women, and to assess the effectiveness of Papanicolaou smears (Pap smears) in preventing invasive cervical cancer in Thailand. Variables that distinguish women at significantly increased risk of invasive cervical cancer, to whom preventive programmes should be directed, include a history of treatment for abnormal vaginal discharge (an indicator of vaginal or cervical infection), a history of venereal disease, and little or no education (an indicator of low socioeconomic status). Risk of invasive cervical cancer decreased significantly as the frequency of Pap smears increased, and was reduced by 75% in women who had at least one Pap smear per year.