Trends in cancer screening

The goal of cancer screening is to detect the illness at its onset, “pre-malignant” stage, when “cure” is conceivable. This is based on the concept that all tumors start small and over time they get larger until they reach a size or a stage where they encroach on adjacent tissues or metastasize. Metastasis refers to the pathologic state when tumor cells, after invading the vascular and or lymphatic systems, end up settling in distant areas of the body, i.e. colon cancer spreading to the liver or lung.

The ideal cancer-screening test should be simple to administer, hence convenient for patients, inexpensive and proven to be sensitive and specific. This is exemplified by the Papanicolaou cervical smear or PAP smear that was introduced in the USA in the middle of the last century. This relatively simple and inexpensive test is credited for the low death rate from cervical cancer not only in this country but the whole world.

Colon cancer is the second most common cause of cancer deaths in adults in this country and screening for this malignancy has evolved over time. A clear understanding of how an adenomatous colon polyp progresses into an adenocarcinoma is the basis of the screening tests available.

For years, the test for the presence of blood in the tool (fecal occult blood testing) was the only non-invasive test for colon malignancy; unfortunately, this was found to lack specificity, meaning that if it is positive it cannot really tell whether it is due to cancer or other non-cancer abnormality; another problem is that some colon cancers do not bleed. Consequently, this has been replaced by the more accurate fecal DNA testing.

However, the most reliable and considered today’s standard is colonoscopy; this is now the recommended screening test for colon malignancy and should be started at age 50. With modern technology, colonoscopic removal of early neoplasms in any segment of the colon is now possible at the time of screening, a process deemed impossible just a few years ago, but clearly beneficial to patients.

Discussion of cancer screening would be incomplete without mention of breast cancer; after all, the widely acclaimed decrease in breast cancer deaths in the past decade is attributed to effective screening which is synonymous to mammography in this country. The debate during the past several years centered on the age when to start screening and whether mammography alone is enough. The U.S. Preventive Services Task Force recommend screening to start at age 50, but the American Cancer Society disagrees and recommends starting screening at age 40.

The bottom line is that clinicians must be aware and able to discuss with patients the reported health risks of mammography and must ultimately base recommendations on patients’ risk factors and the patients’ wishes.

Today’s reports on this subject also point out that self-breast examination is not helpful and unnecessary, in the face of digital mammography that has enhanced capability of detecting small lesions. There is consensus that in very dense breasts, mammography and ultrasound should be done routinely, although MRI would give better results. There is a suggestion that in cases of familial breast cancer, mammography, MRI and genetic testing should be part of the screening test.

Recently, the guidelines for lung cancer screening were established. Lung cancer is the foremost cause of cancer deaths for both men and women in this country. The protracted scientific studies and debate on this issue ended with the conclusion that annual low dose CT imaging could successfully detect lung cancer before it becomes symptomatic thereby improving survival rate. So, the United States Preventive Services Task Force (USPSTF) recommends that lung cancer screening should be done on “adults ages 55 to 80 who have a 30 pack-year smoking history and who currently smoke or have quit within the past 15 years;” although, the final message is: “avoiding smoking is the best way to prevent lung cancer!”

Reference: Selected Readings in General Surgery. General Oncology, Part I, V40N1

Dr. Cabasares is board certified general surgeon and Fellow of the American College of Surgeons. He practices in Perry.

HHJ News