Appropriate frequency of mass-screening for uterine cervical cancer

Between 1973 and 1983, 250,264 Japanese women in Shimane Prefecture were mass-screened for uterine cervical cancer. A malignancy was detected in 218. Carcinoma in situ (CIS)-(stage 0) was present in 92 (42.2%) and 126 (57.8%) had an invasive cancer (stage Ia or above). Of the 218, only 90 (41.3%) had undergone previous mass-screening. The history of these 90 (stage 0: 45, stage Ia or above: 45) was examined retrospectively to determine appropriate frequency of mass-screening for uterine cervical cancer in CIS. 1) Three (6.7%) out of 45 patients with invasive cancer were found within 12 months after the last mass-screening, the number being definitely small compared with the 20 (44.4%) found within 24 months (p less than 0.01). 2) Three (21.4%) out of 14 patients with malignancy found within 12 months after the last mass-screening taken were diagnosed as cases of invasive cancer, the number being definitely small compared with the 17 (56.7%) patients with invasive cancer out of 30 patients with malignancy found within 12 approximately 24 months (p less than 0.05). 3) 3/45 (6.7%) had an invasive cancer, despite yearly mass-screening for 3 years. The previous cytological assessment was class I or II and the previous colposcopical examination revealed no abnormal findings. 4) Of the 45 with CIS, 11 (24.4%) underwent yearly mass-screening for over 3 consecutive years. I conclude that mass-screening for uterine cervical cancer should be done once a year.