Several risk factors for cervical dysplasia are well established. Risk factors interact and may be additive, so it is usually difficult to say that a given factor is responsible for any one case of cervical dysplasia or cancer (La Vecchia 2014; Arnheim Dahlstrom 2011; ACS 2014b).
HPV is involved in virtually all cases of cervical dysplasia (Hogewoning 2003; Schiffman 2007; NCI 2012). The types of HPV that cause cervical dysplasia are usually sexually transmitted (ACS 2014b; Hogewoning 2003).
HPV comprises a group of more than 200 related viruses (NCI 2012). Each virus in the group is given a number, which is called an HPV type or strain (Kumar 2013). At least 12 HPV types are associated with cancer (NCI 2012). HPV type 16 is the most likely to cause cancer: it is closely associated with roughly 55–60% of cervical cancer cases in the world, and CIN II caused by HPV 16 may be less likely to regress than CIN II caused by other high-risk strains (ACOG 2013a; Castle 2009). HPV 18 is the next-most-likely to cause cancer, accounting for 10–15% of cervical cancer cases (ACOG 2013a). Eight other high-risk HPV strains (types 31, 33, 35, 45, 51, 52, 56, and 58) are associated with the great majority of other cases of cervical cancer (Wheeler 2009; de Sanjose 2010).
HPV infection occurs most frequently in teenagers and women in their early 20s (ACOG 2013a). Prevalence of HPV infection increases from age 14 to 24 but then gradually declines through age 59 (Dunne 2007). Young women, especially those 21 or younger, usually clear the infection by means of their immune response in an average of eight months (ACOG 2013a). Most associated cervical abnormalities will also spontaneously resolve among these women (Moore 2007; Fuchs 2007).
Other Risk Factors
Immunosuppression. Women receiving immunosuppressive therapy for autoimmune disease or cancer, or because of an organ transplant, are at increased risk of cervical dysplasia progressing to cervical cancer (Dugué 2013; ACOG 2014). Those with HIV/AIDS also have compromised immunity, which increases the risk for cervical dysplasia and cervical cancer (Davis 2001; Schafer 1991; Abraham 2013).
Smoking. Smoking increases the risk of many cancers, including cervical cancer (Silva 2014). Fortunately, research appears to show that quitting smoking reduces the risk of CIN III and cervical cancer (Roura 2014).
Diethylstilbestrol exposure. Daughters of women who took the synthetic hormone diethylstilbestrol (DES) during pregnancy are at increased risk for dysplasia and cervical cancer (NCI 2011a). DES has not been prescribed to pregnant women in the United States since 1971; thus, most DES-exposed women are currently beyond their childbearing years (Casey 2011).
Ethnicity. In the United States, women of different ethnicities have different degrees of risk of cervical cancer. Those most likely to develop cervical cancer are Hispanic women, followed by African-Americans, Asians and Pacific Islanders, and Whites, with the lowest risk found among American Indians and Alaskan natives (ACS 2014a).
Pregnancy-related risk factors. A woman’s pregnancy history appears to impact her risk for developing CIN and cervical cancer. For reasons not fully understood, three or more full-term pregnancies seem to increase the risk of developing cervical cancer. Additionally, women whose first full-term pregnancy occurred before age 17 are nearly twice as likely to develop cervical cancer later in life compared with women whose first pregnancy occurred at age 25 or older (ACS 2014b; Weppner 2014).
Oral contraceptives (birth control pills). Taking oral contraceptives for prolonged periods of time appears to increase the risk of cervical cancer. One study reported that cervical cancer risk doubled in women on birth control pills for more than five years, but found the risk returned to normal 10 years after they were discontinued (ACS 2014b).
Sexual history. Early sexual activity, during puberty or before age 18; having multiple sexual partners; and having a male partner who has had multiple sexual partners all increase a woman’s risk. Condoms provide some degree of protection from the spread of HPV as well as other sexually transmitted diseases when used consistently and properly (Weppner 2014; Zanotti 2014; ACOG 2014; ACS 2014b). One study found that condom use significantly promotes regression of cervical dysplasia, even of CIN II or higher (Hogewoning 2003).
Body weight. An observational study of 1125 women aged 18–65 years who had an HPV infection found that overweight women were at 25% increased risk of cervical cancer, while mildly obese women had 70% increased risk (Lee 2013). Also, overweight and obese women are at greater risk of dying from cervical cancer (Wee 2000).
Family history of cervical cancer. Women whose mother or sister had cervical cancer are at two to three times the risk of developing the disease themselves (ACS 2014b).
Chlamydia infection. Chlamydia is a sexually transmitted disease that often causes no symptoms. Women with a history of chlamydia infection appear to be at increased risk of cervical dysplasia and cervical cancer. A history of other sexually transmitted disease is also associated with increased risk of cervical dysplasia and cancer (ACS 2014b; Jensen 2014).