40 YEARS OF REPEATED SCREENING - THE SIGNIFICANCE OF CARCINOMA IN-SITU

Two cohorts of women born in 1914-18 and 1929-33 who participated in a cervical screening programme have been followed for over 40 years. Ag e-specific incidence rates of squamous carcinoma of the cervix by rank ; of smear and length of Interval between smears are reported. The you nger cohort, who had undergone more frequent screening, had lower rate s of invasive disease. From these incidence rates, estimates of false- negative rates and regression rates for carcinoma in situ have been ma de. The false-negative rate was estimated to be about 15%. Regression seemed more frequent in younger than in older women. For the younger c ohort it was estimated to be 72% and in the older 47%. A comparison of the rates of in situ carcinoma with those of invasive disease suggest s that the screening of the younger cohort reduced the rare of invasiv e disease to at least one-half or one-third of what it would have been if screening had commenced later. Rates of disease appear less depend ent on age than previously thought and are consistent with causation b y an infective agent.