Although a number of factors contribute to the development of cervical dysplasia, most cases involve exposure to the human papillomavirus (HPV), a common virus that also causes warts. HPV is spread through skin-to-skin contact, including sexual activity (ACS 2014b), and nearly all sexually active men and women will contract HPV at some point in their lives (Fiks 2014; ACS 2014b; CDC 2014). There are numerous strains of HPV. Some are much more likely to cause cellular abnormalities or cancer than others, and are denoted “high-risk” HPV types.
Cervical cancer rarely develops in women younger than age 20; most cases occur in midlife and in women under age 50. However, more than 20% of cervical cancer cases occur in women over 65. Most cases in women over 65 occur in those who did not undergo regular screening with Pap tests before age 65 (ACS 2014a).
Cervical cancer usually develops over a period of several years (ACOG 2014). During this time, the cells on or around the cervix become abnormal. The cellular abnormalities that occur before cancer is present are usually called cervical intraepithelial neoplasia (CIN). “Intraepithelial” denotes that the changes occur within the cervical cells, and, in the case of precancerous growths of the cervix, “neoplasia” refers to uncontrolled cell growth.
Cervical dysplasia and cervical cancer are classified along a spectrum of increasing cervical cell abnormality. The goal of classification is to determine the degree to which the cervical cells have become abnormal, and whether treatment is needed, since lower degrees of dysplasia may resolve on their own without treatment. CIN is grouped into three categories (Storck 2014; OSU 2015):
- CIN I (mild dysplasia)
- CIN II (moderate dysplasia)
- CIN III (severe dysplasia to carcinoma in situ)
The latest classification scheme is the Bethesda system (IARC 2014; NCI 2002). In the Bethesda system, low-grade squamous intraepithelial lesion (LSIL) encompasses CIN I; and high-grade squamous intraepithelial lesion (HSIL) includes CIN II and III (IARC 2014).