“…Invasive carcinoma occurs in patients with an average age of approximately 50 years and carcinoma in situ is thought to be present for ten to twelve years before the onset of invasion (38.7 years, Hertig and Younge, 1952;38 years, Scaramucci et al, 1958;38 years, McKay et al, 1959). Even with a possibly later onset in life (43.4 years, Mussey and Soule, 1959;42 years, Henderson and Buck, 1961) there still remain at least 5 years during which the progression or regression of carcinoma in situ can be assessed. It has been shown by Kern (1959) that it is possible to differentiate, by cytological methods, between carcinoma in situ and invasive carcinoma.…”