We know that the incidence of cervical cancer is decreasing in Europe. However, the evidence that this regression is due to screening of the female population with the Pap test is not easy to come by. Clinical trials in two similar populations of women, one tested and the other untested for several years in an attempt to find differences in morbidity and mortality from cervical cancer, would be indefensible in ethical terms. This means that we are forced to use the results of observational studies of the prevention of cervical cancer in populations in which other factors (changes in sexual habits, hygiene, barrier contraceptive methods, improvements in health conditions in the home, etc.) are difficult to control for.
Although cervical cancer is the second most frequent type of cancer in women worldwide, the great majority of women (80%) with this disease live in developing countries.
In Spain the incidence is the second lowest in the world: mortality due to cervical cancer accounts for only 0.3% of all deaths among Spanish women.
We know that human papilloma virus (HPV) infection, cervical cancer and precursor lesions are strongly associated with each other in a consistent, specific manner. Of the 30 types of cancer that can arise in the cervix, this association has been demonstrated for types 16 and 18, although other types of cancer may also be related. Among existing methods to detect infection are Southern blotting, the most sensitive technique although expensive and complex to use, and dot blotting. Until recently the latter required radioactive materials, although this problem might be solved with the liquid phase hybrid capture method. However, the routine use of these methods is far from advisable because of our inadequate knowledge of the natural history of the disease.
Demonstrated HPV infection is unspecific and poorly predictive of the subsequent development of cervical cancer. However, the predictive value of the Papanicolau test for atypia of squamous cells of unknown significance (ASCUS) and low-grade lesions would be greater if HPV infection could be tested in these women.
Other risk factors, although supported by less evidence, are HIV infection, early initiation of sexual relations and number of partners, low socioeconomic status, smoking, and a diet poor in carotenes and vitamins A and C.
This issue of Atención Primaria contains an interesting article titled "Use of Pap Tests for Cervical Cancer Screening and Factors Related With Use in Spain," by doctors Setefilla Luengo and Ana Muñoz. This population survey, carried out as part of an intramural research project financed by the Instituto de Salud Carlos III, finds that only 49% of all women between the ages of 40 and 70 years have had one or more Pap tests in the last 5 years. The factors associated with use of the test were intention to have a Pap test in the future, considering the test to be necessary even in the absence of symptoms, fear of the diagnosis not being an obstacle, having had a previous Pap test, and doctor's advice to have the test.
According to this study, having the test is related with upper or middle-upper socioeconomic status (groups in which the incidence is lower, a paradox possibly resulting from private medical care in this sector of the population), private or combined health care, age between 40 and 50 years, and residing in a city with a population larger than 100 000. Testing was also associated with factors such as marital status, size of the town or city of residence, highest level of education completed, employment status, number of children, number of pregnancies, type of health care coverage, having a Pap test in the preceding 5 years, knowing a relative or friend with cervical cancer, perceiving the test as safe, and perceiving cervical cancer as a curable disease.
After more than 20 years of constant reforms in the Spanish national health service, it is hard to accept that more than half (51%) of the women without symptoms had not had a Pap test in the last 5 years. Even worse, the population with fewest resources, who rely almost exclusively on public health care services, is the one that would benefit most from this preventive intervention. The authors found no statistically significant association between having a Pap test and visits to the general practitioner in the preceding 3 years or the perceived likelihood of cervical cancer in comparison to other women the same age.
This study appears to show that health professionals and the general population remain relatively unaware of this health problem. However, before a decision is made to devote additional efforts and resources to preventive measures, we should assess the factors that curtail the efficiency of such measures in our setting:
The low frequency of this type of cancer limits the predictive value of the test.
Our knowledge of the natural history of the disease is limited. We do not know what percentage of premalignant lesions will progress to give rise to cervical cancer and how many will regress without treatment.
The high proportion of false negatives and false positives in the Pap test in studies done in developed countries with preventive programs going back several decades, such as the United Kingdom, the USA, and Canada.
The different classification systems now in use at different pathology laboratories in public hospitals and private clinics.
The low rate of uptake by women, especially those who comprise the population at risk.
Recommendations of the PAPPS
The 2003 update of the Programa de Actividades Preventivas y de Promoción de la Salud (PAPPS) worded with a commendable degree of caution, has reached the following conclusions on the basis of epidemiological characteristics and scientific evidence:
" Appropriate consensus is advisable on protection during sexual contacts.
The Papanicolau test is recommended. Initially, 2 annual tests should be done, followed by a test every 5 years in sexually active women aged 35 to 65 years. Women older than 65 years who have not had a test in the last 5 years should be advised to have 2 annual tests. If both tests are normal, no further interventions are advisable.
Women with risk factors should be actively sought out."
These recommendations should lead to fewer interventions during a woman's lifetime than those recommended by the Canadian Task Force and the United States Preventive Services Task Force, both of which propose earlier and more frequent interventions.
In the light of current knowledge of epidemiological findings in Spain, should primary care professionals work to spread the use of the Pap test? I believe the recommendations of the PAPPS are reasonable, and reflect the as yet inconclusive evidence available regarding a number of aspects in the prevention of cervical cancer.
In view of the results of the study by Luengo and Muñoz, we should devote greater efforts to outreach for groups at greatest risk. Immigrant women, who receive care almost exclusively through public rather than private health services, form part of a collective at risk. Most of these women are from countries where the incidence of the disease is higher than in Spain, where marriage takes place at an earlier age, and where fertility rates are different from that of Spain. Moreover, these women often belong to disadvantaged socioeconomic groups.
What is the future likely to hold for cervical cancer prevention? Will we have an inoculable vaccine in the next few years for women at moderate to high risk? Will simple techniques become available to detect papilloma virus infection in women with low-grade malignancy lesions or patients at high risk? This group of patients would include immigrants arriving from countries where the prevalence of cervical cancer is high, carriers of HIV infection or persons with AIDS, and heterosexual women with multiple partners.
The data obtained from the research by Luengo y Muñoz are highly useful. However, many unanswered questions remain with regard to decisions as to whether to devote more resources to programs for the prevention of cervical cancer in the general population in Spain. Once the right information and appropriate resources are available, the priority given to the prevention of this cancer can be suitably modified with respect to other types of cancer that cause similar or higher rates of morbidity and mortality among the women we care for.
Key Points
* Our knowledge of the natural history of cervical cancer is insufficient.
* The association between human papilloma virus and cervical cancer is strong, consistent and specific. However, viral infection in the absence of Pap test results is poorly predictive of the appearance of cervical cancer.
* Half of all women in Spain between the ages of 40 and 70 years have had at least one Pap test in the preceding five years.
* Studies are needed to evaluate the impact of well-established programs in Spain on mortality from cervical cancer in different autonomous communities.
