The risk depends on:
- Type of HPV
- Other risk factors in the individual woman
- Time allowed for progression.
Modelling and follow-up studies have estimated progression rates between 12% and 40% (Gustafsson & Adami 1989; Ostor 1993; Peto et al. 2004; McCredie et al. 2008).
The interval between carcinoma in situ (peak incidence age 30 years) and invasive cancer (peak age 43 years) suggests an average interval of 13 years before invasion takes place (Gustafsson & Adami 1989).
Cancers in younger women, suggesting a shorter interval, are more likely to be caused by HPV16 and 18 than later in life (Carozzi et al. 2010).
The likelihood of progression of CIN3 to invasion has been estimated at 1% per year (McCredie et al. 2008).
Cytological diagnosis of low-grade and high-grade lesions
- Cytological diagnosis of low-grade squamous intraepithelial lesion (LSIL), which can also be described as mild or low-grade dyskaryosis (UK) or mild dysplasia (many countries in Europe). LSIL on cytology correlates to CIN1 on histology.
- Cytological diagnosis of high-grade squamous intraepithelial lesion (HSIL) and high-grade dyskaryosis (UK) may be qualified as moderate or severe dyskaryosis (UK), moderate or severe dysplasia or favour CIN2 or favour CIN3 in the Bethesda system. HSIL on cytology correlates to CIN2 and CIN3 on histology.