Population Screening for Cervical Cancer - Term Paper Example

Population screening, in the context of medical practice, is the use of easily implemented tests across a population to identify individuals who havea disease. Population screening for cancer is a way of controlling cancer incidence and mortality. Cervical screening in particular is important because cervical cancer is preventable (pre-cancerous cervical cells are detectable) and can be stopped if detected early. The goal of screening examinations for cervical cancer is to find pre-cancerous cells before they develop into actual invasive cancers ("Screening and Early Detection," 2006 ). Early detection and treatment prevents 75 percent of cervical cancer cases from developing ("NHS Cervical," 2006). Currently mass population screening is considered justifiable only for breast cancer and cervical cancer ("Screening and Early Detection," 2006). Before a screening program is implemented on a population, there are some essential considerations that must be focused on: the effectiveness and feasibility of the test should have been ascertained; the resources, such as manpower and equipment, should be sufficient to test the population; the diagnosis and treatment of those who test positive should be implementable; and the cost of the screening (money and effort-wise) should be justified by a sufficiently high prevalence of the disease ("Screening and Early Detection," 2006 ). It must be considered that screening, when done too frequently, will result in more false positives and more diagnostic tests, which means time and money will be wasted, so the frequency of screening should only be sufficient enough to ensure that the disease will not progress beyond a pre-cancerous stage ("Screening for Cancer," 1999). Furthermore there are some important factors to consider with any screening method. First, the sensitivity, or the cancer detection rate should be sufficiently high. The positive predictive value is the measure of the accuracy of positive results, concerning how much of the population who tested positive actually do have, or will develop, the disease. The negative predictive value, on the other hand, pertains to the accuracy of negative results. If a large proportion of subjects with negative results turn out to actually have the disease, this is an indication of a low negative predictive value. The specificity, on the other hand, is the converse of the negative predictive value; it is the measure of the extent at which individuals without the disease are tested negative. The acceptability of a screening technique depends on the individuals to be tested; it is the extent at which individuals are willing to undergo the test. This is where the common cervical screening technique, the Pap smear, may fail in some conservative locations. A screening.technique should have high sensitivity and specificity. ("Screening for Various Cancers," 2006) The basic intent in screening is to identify individuals with an early stage of the disease so that they can be treated more effectively. Screening is done to asymptomatic individuals. Cervical screening is repeated at intervals based upon the natural history of cervical cancer, as determined from documented cases ("Screening for Cancer," 1999). Generally only women from the ages of 25 to 65 need to regularly undergo cervical screening. In teenaged females, the still-developing cervix may test postive when it is in fact healthy. Cervical cancer in females under the aged of 25 are exteremly rare. Also, women of age 25 to 64, but who have never had sexual intercourse with a man, have a very low risk of developing cervical cancer. ("NHS Cervical," 2006) Cervical screening is done either with a Pap smear or the newer method of Liquid-based Cytology (LBC) ("NHS Cervical," 2006). Cytology screening using the Pap smear is the generally accepted method of cervical cancer screening. Currently the Pap test is the only test known to have reduced cervical cancer incidence, and increase survival rate, when implemented in an organized screening program ("Cytology Screening," 2006). Among the advantages of Pap cytology are its high specificity. It can also be easily adapted to computer-assisted reading and interpretation. Cytology is also a low cost method, and identified lesions are easy to treat ("Cytology Screening," 2006). However, in a regular Pap smear test, it is possible that infection of the vagina or cervix cause pus, increased mucus production, yeast, or bacteria that will obscure the cells under consideration. Another disadvantage of this method is that cells may become distorted when drying out ("Can Cervical Cancer," 2006). Another limitation of Pap cytology are that the test (whether Pap smear or LBC) is invasive, requiring insertion of instruments into a woman's vagina, hence it may be embarrassing for some patients. It also requires that the persons administering the procedure have undergone extensive training. In the case of Pap smears, the adequacy of the sample is not immediately determinable, hence it is possible that women will be recalled for a repeat procedure. ("Cytology Screening," 2006) Although generally successful, Pap smear cytology has some significant constraints, particularly its low negative predictive value. The newer method of obtaining cervical samples for testing is Liquid-based cytology. In LBC, a sample from the cervix is obtained using a specialized spatula. Instead of smearing the sample onto a microscope slide, the head of the spatula is either broken off into or rinsed directly in a preservative fluid. The fluid is spun and treated to remove unnecessary material such as mucus, bacteria, pus, and yeast. A sample of the remaining cells is then taken and viewed under a microscope by a cytologist. LBC also prevents sample cells from drying out and becoming distorted. There have been recent studies that show that LBC has a much better detection rate of pre-cancerous cells than the traditional Pap smear, and the number of tests that need to be repeated are greatly reduced. ("NHS Cervical," 2006) To ensure that the results of a Pap test are as accurate as possible, some guidelines should be followed. Anything that may deposit extraneous material or touch the linings inside the vagina, particularly the cervix, should be avoided; hence the Pap test should not be done during menstruation. Douching, sexual intercourse, tampons, birth control foams and the like should not happen 48 hours before the test. ("Can Cervical Cancer," 2006) 90 percent of Pap test results are normal, and about 5 percent show mild cell changes. In most of these positives the cells will eventually become normal without intervention, so only repeat tests every six months is necessary, unless the cells do not become normal. 1 percent of tests show moderate cell changes, and 0.5 percent show severe changes. Less than 0.1 percent, or 1 in 1000, will show actual cancer. ("Cervical Cancer Screening," 2002) If a Pap test results in a positive, the result is presented in one of two ways. The subject may be informed that she has mild, moderate, or severe cell changes (dyskaryosis). The test result may also be presented as a CIN 1, CIN2, or a CIN 3. CIN stands for cervical intraepithelial neoplasia, meaning that there is a high probability that there are cervical cell changes. The numbers 1, 2, 3 mean mild, moderate, and severe cell changes, respectively. These three levels pertain to the proportion of abnormal cells in the epithelium covering the cervix, where 1 stands for one-third, 2 for two-thirds, and 3 for 100 percent abnormality. ("Cervical Cancer Screening," 2002) When a Pap test gets result of a mild cell change or CIN 1, either a colposcopy will be performed on the subject, or she will be asked to be retested after six months. If the repeat test still shows abnormalities, a colposcopy becomes necessary. In the case of moderate or severe cell changes, or CIN 2 or 3, the subject will be given treatment to remove the abnormal cells. This treatment is done twice, after which follow up Pap tests will be done. ("Cervical Cancer Screening," 2002) In some cases a CIN 3 is a 'carcinamo in situ'. In such a case the cells appear cancerous, but are still contained within the epithelium of the cervix. This is still considered 'pre-cancerous', and will only be considered an actual cancer when the abnormality breaks through the epithelium and spreads into surrounding tissue. Immediate treatment is necessary in this case. ("Cervical Cancer Screening," 2002) Although more expensive, the main advantage of LBC is that the proportion of inadequate/unusable samples is significantly reduced, thus recall of women for second tests are reduced as well. Results are also obtained quicker. In the sites that have implemented LBC, the proportion of inadequate smears was reduced from 9 percent to about 1 or 2 percent. ("NHS Cervical," 2006) Another improvement to the Pap test is the AutoPap. It uses computerized instruments that can detect abnormal cells. The AutoPap has been approved by the US Food and Drug Administration (FDA) for initial testing of Pap samples instead of by a cytologist, although samples tested as positive by the AutoPap will still be examined by a cytologist. The AutoPap can find abnormal cells that are missed by a cytologist, and can be used for retesting samples that were interpreted as normal. ("Can Cervical Cancer," 2006) It is established in the medical community that there is a strong association between cervical cancer and infection with particular subtypes of the human papilloma virus. The general consensus among organizations on screening reccomendations for cervical cancer; most agree that screening should begin when a woman starts to engage in sexual activity, or when the woman turns 18 years old, whichever comes first, reflecting the fact that cervical cancer has a strong association with sexually transmitted viral infections, particularly that of the human papilloma virus. After three consecutive tests will all negaive results, further screening can be done less frequently, at the discretion of the physician. (Smith, Mettlin, Davis, & Eyre, 2000) References Can cervical cancer be prevented (2006). In Detailed Guide: Cervical Cancer. American Cancer Society. Retrieved March 16, 2006, from http://www.cancer.org/docroot/CRI/content/ CRI_2_4_2X_Can_cervical_ cancer_be_prevented_8.asp. Cervical cancer screening. (2002). In About cervical cancer. Cancer Research UK. Retrieved March 16, 2006, from http://www.cancerhelp.org.uk/help/default.asppage=2756. Franco, E.L. (2003). Primary Screening of Cervical Cancer with Papillomavirus Tests. Journal of the National Cancer Institute Monographs, 31: 89. Cytology screening. (2006). In Screening and early detection of cancer. World Health Organization. Retrieved March 16, 2006, from http://www.who.int/cancer/detection/ cytologyscreen/en/index.html. NHS cervical screening programme. (2006). National Health Service. Retrieved March 16, 2006, from http://www.cancerscreening.nhs.uk/cervical/. Screening and early detection of cancer. (2006). In Cancer. World Health Organization. Retrieved March 16, 2006, from http://www.who.int/cancer/detection/en. Screening for cancer. (1999). The BC Cancer Agency. Retrieved March 16, 2006, from http://www.bccancer.bc.ca/HPI/ CancerManagementGuidelines/ScreeningforCancer.htm. Screening for various cancers. (2006). In Screening and early detection of cancer. World Health Organization. Retrieved March 16, 2006, from http://www.who.int/cancer/detection/ variouscancer/en/index.html. Smith, R.A., Mettlin, C.J., Davis, K.J., & Eyre, H. (2000). American Cancer Society guidelines for the early detection of cancer, 2003. CA: A Cancer Journal for Clinicicians, 50:34-49. Read More