Cervical cancer screening: Why less is best
Severe dysplasia of the cervix. Cervical smear, showing clusters of abnormal cells (stained orange).
Each month, The Clinical Advisor makes one new clinical feature available ahead of print. Don't forget to take the poll. The results will be published in the next month's issue.
In 2012, the American Congress of Obstetricians and Gynecologists (ACOG) updated its recommendations regarding the starting age and frequency of Papanicolaou (Pap) smear testing. It is now recommended that the test, an important screening tool for cervical cancer, start later and be performed less frequently for most women.
Many healthcare providers have expressed confusion and concern regarding the new guidelines. This article examines the rationale for screening, reviews the recommendations in the latest guidelines, and seeks clarity on the best evidence-based practice.
Disparity between guidelines and practice
Use of the Pap smear test as a tool for screening for cervical cancer has significantly reduced the incidence of the disease in the United States.1 Before Pap smear testing began to be used in 1945, cervical cancer was the most common cause of cancer deaths in women.2 According to the most recent data available from the National Institutes of Health,3 cervical cancer is now the 14th most frequently diagnosed cancer in American women.
In 2009, and again in 2012, the ACOG released updated recommendations lengthening the time between screenings from the traditional yearly Pap smear to every 3 years for most women.4 However, one study found that most healthcare providers still recommend yearly Pap smear tests to patients who qualify for less frequent testing under the current guidelines.5
Transient human papillomavirus infection
Infection with high-risk types of human papillomavirus (HPV), which is transmitted via sexual contact, has been linked to almost all cases of invasive cervical cancer.6 Other risk factors for cervical cancer include smoking, high parity, young age at first intercourse, and long-term use of oral contraceptives.7
There is a high incidence of HPV infection in women by their early 20s, yet these infections are largely transient and rarely lead to lasting cervical cell changes. Invasive cervical cancer in women younger than age 20 is a statistic rarity, with only 0.05 cases per 100,000 women in the United States.7 Even in the presence of advanced cervical dysplasia, women in this age group typically have regression of the abnormal cells, and they rarely develop cervical carcinoma. In one study, 93% of women aged 16 to 23 years with normal Pap smear test results but who were positive for types 16 and 18 HPV—the most likely subtypes to cause cancerous changes—had cleared the virus in 36 months.7 Another study revealed that more than 90% of women with both positive HPV test results and early abnormal cell changes on Pap smears had cleared the HPV infection 2 years later.7
The transient nature of HPV infection in younger women led the ACOG to recommend in their latest guidelines that in the absence of risk factors, women should begin Pap testing at age 21, regardless of their age of first intercourse.8 Earlier recommendations by the ACOG advised Pap testing begin 3 years after women became sexually active, or at age 21, whichever came first.9 The current guidelines list certain personal factors that warrant earlier testing, which include positive human immunodeficiency virus status, being in an immunocompromised state, or previous treatment for cervical abnormalities.8
Slow development of cervical cancer
Cervical cancer is a disease that progresses slowly, and it is preceded by a lengthy period of precancerous cell changes prior to the development of the cancer. These precancerous changes often spontaneously regress with no treatment. Data suggest that the presence of the lowest level of change, cervical intraepithelial neoplasia (CIN) 1, does not lead to a significantly increased risk for development of the highest level of dysplasia, CIN 3.7 Up to 43% of patients with CIN 2 and 32% of those with CIN 3 have remission without development of cervical carcinoma.7
When the highest level of dysplasia persists, it typically takes 10 years to result in invasive cervical cancer.10 The incidence of CIN 3 peaks in women in their late 20s, whereas the incidence of cervical carcinoma peaks in women in their 40s, giving support to the indolent nature of cervical cancer.7 The period between appearance of dysplasia and development of cancer allows a lengthy window for treatment of abnormal cells with various methods, such as the loop electrosurgical excision procedure (LEEP); in almost all cases, the prevention of invasive carcinoma is achieved with this procedure.
It should be noted that many women, by some estimates nearly 50%, who are diagnosed with cervical carcinoma have never had a Pap smear test prior to the one that leads to the diagnosis of cancer.11 Another study revealed that more than 50% of women diagnosed with cervical cancer had not been screened for cervical cancer within the 3 to 5 years prior to their diagnosis.7