Levine_Handbook for Principles and Practice of Gynecologic O

Chapter 4 Preinvasive Lesions of the Genital Tract 79

TABLE 4.1 Natural History of CIN Is Dependent on Lesional Grade

% Regression

% Persist

% Progress to CIS

CIN 1

57

32

11

CIN 2

43

35

22

CIN 3

32

56

12

high-grade lesion. Mathematical modeling studies based on the prevalence of cytologic abnormalities in an unscreened population suggested that it takes on average almost 5 years for mild dysplasia to progress to severe dysplasia. More recent studies contradict this model and suggest that high-grade lesions can develop quite rapidly after an incident HPV infection. A prospective study of college students found that the median length of time from the first detection of an HPV infection to the detection of CIN 2,3 was only 14.1 months. Data from HPV vaccine trials confirm that CIN 2,3 lesions can develop quite rapidly after initial HPV infections. Due to concern for progression from CIN 1 to CIN 2,3, low-grade lesions have traditionally been treated. However, prospective studies have shown that many low-grade CIN 1 lesions spontaneously regress and have a low chance of progressing to CIN 2,3 or squamous cell carcinoma. Whether CIN 2,3 can spontaneously regress remains controversial (Table 4.1). Vulva Studies on the natural history of VIN lesions are much fewer than for CIN. Thus, the relationships between VIN and invasive squamous cell carcinoma of the vulva are less well understood than those documented between CIN and invasive squamous cell carcinoma of the cervix. Unlike the cervix, in which the majority of carcinomas are associated with high-grade dyspla sia, only one-third to one-half of invasive vulvar squamous carcinomas have a coexisting VIN 3 lesion. A review of six published follow-up studies found that only 16 of 330 patients (4.8%) with VIN progressed to invasive cancer. Most of the patients in these follow-up studies were treated for their VIN or followed for relatively short periods of time, which limits our understanding of the natural history of these lesions. Risk Factors for the Development of Lower Genital Tract Cancers and Preinvasive Lesions of the Lower Genital Tract Key Points ● Smoking and number of sexual partners are the greatest risk factors for cervical cancer and its precursors. ● HPV infection is acquired through sexual contact and is necessary for the development of cervical cancer and its precursors. ● The majority of HPV-infected women spontaneously clear their infections within 1 to 2 years.

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