As HPV-DNA testing methodology evolved and improved in sensitivity and specificity, HPV was detected in 75-90% of precancers (SILs) and 99% of invasive cancers (14). The lower prevalence rate of HPV in the SILs compared with invasive cancers is likely because of misclassification of SIL, particularly LSIL. The higher the grade of the lesion, less likely there is misclassification and more likely HPV is detected (15). The prevalence of HPV is higher in younger women than older women, but the overall prevalence of high grade lesions is lower in young women.
Younger women have HPV rates up to six to eightfold than that of older women. Prevalence rates range from 12 to 56% in women under 21 years compared with 2-7% in women more than 35 years of age (4,5,16,17). Although, some countries have prevalence rates that begin to rise again after the age of 50 years, the rates do not reach to those of young women (18). Approximately, 50% of adolescents and young women acquire a cervical HPV infection within 5-7 years after initiating sexual intercourse with the highest risk factor being a recent new sexual partner (19). As previously discussed LSIL is the morphological manifestation of cervical HPV infections and high rates of LSIL would therefore be expected in this group. Rates of LSIL range from 2 to 14% (20-22) in adolescents whereas in older women (>30 years) the rates range from 0.6 to 1%. However, it is important to emphasize that HPV detection in adolescents is most commonly associated with normal cytology. More than three-quarters of infected adolescents have normal cytology (19).
Rates of high-grade SIL (HSIL) are substantially lower in adolescent populations. Mount and colleagues (8) examined more than 10,000 Pap smears from young women in New England and found that 14% of the smears from women aged 15-19 years were abnormal with only 0.7% having HSIL and no cases of invasive cancer. In this same cohort, approx 0.8% of women aged 20-29 years and 0.7% aged 30-39 years had HSIL. Although, these rates are similar, biopsy-proven HSIL is generally higher in older women. In a nationwide organized cervical screening program in Norway, 0.2% of 20,000 smears from adolescents aged 15-19 years were reported as having HSIL (21). The high rates of SIL, predominantly LSIL was responsible for referring large number of young women to colposcopy in the United States in the 1990s as LSIL was considered by many at that time to be a precancerous lesion. Moreover, there was a consensus that setting HSIL as the threshold for referral to colposcopy was too high.
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