[Optimal frequency of cervical cancer cytology for mass-screening]

It is recommended that, as a general rule, all asymptomatic women in Japan undergo cervical cytology for cancer detection once a year. However, a new guideline issued by the American Cancer Society states that screening frequency may be reduced to once every three years except in certain cases. In our cancer screening program, a total of 434,773 women who had cervical cytology were evaluated according to cytological abnormalities and the following results were obtained: 1) The prevalence of cancer in women examined for the first time (0.175-0.42%) was lower after repeated examinations (0.02-0.03%) and gradually reached the incidence rate. 2) Less that 0.016% developed cervical cancer after continuing to have a Class I grading for two years and we failed to detect invasive cancer in these cases. It is therefore considered sufficient for them to have a Pap test once every two years. 3) When we employed more limited criteria than those of Papanicolaou's classification, we derived a lower incidence rate for those who had maintained a Class I grading for two years continuously. 4) There was a remarkably high prevalence rate in old women, and because there are as yet no established criteria for atrophic smear cytology, we could not fix on the most desirable frequency of cervical cancer cytology for them.