Cancer : Survival Increased, Biotech Tests

by Food and Drug Administration (FDA)

(Page 2 of 3)

Survival Increased

Improved detection and diagnosis have bettered the odds against the disease. Half of cancer patients now survive at least five years, while only a third survived a generation ago. If new diagnostics can spy cancers before metastasis, this rate could improve further.

Even when tests reveal that metastasis has already occurred, they can benefit the patient by eliminating the need for exploratory surgery. Moreover, they point physicians toward the most appropriate treatment approach.

Methods already in use have contributed greatly to reduce cancer deaths. The Pap test has been valuable against cervical cancer. CAT (computed axial tomography) scans, which provide three-dimensional images of the body, are significant advances over one-dimensional x-rays for detecting tumors. However, for definitive diagnosis, the CAT scan's usefulness is limited. A scan shows the presence of a lump but doesn't usually identify its nature. A tissue biopsy is usually needed for definitive diagnosis of the mass it has detected.

'New Biotech' Tests

Tests based on the "new biotechnology" supplement CAT scans, indicating the nature of any abnormalities they may reveal. "New biotechnology" tests work both in the test tube and in patients. Scientists are now able to apply monoclonal antibodies (MAb's) or gene probes to the surfaces of cancer cells. This technology works by recognizing tumor "markers," usually molecules present on the surfaces of cancer cells or shed by them. In the near future, the new biotech tests likely will supplement others, rather than replacing them.

The DNA found in every living cell is the key to such diagnostics. The uniqueness of small strands of DNA makes it possible to detect specific oncogenes and other markers of cancer in the test tube, using probes designed specifically to detect the genes that are marked with a radioactive (or sometimes non-radioactive) label. The MAb rushes to the abnormality it was designed to complement, if one is present.

A test-tube diagnostic called the B/T Gene Rearrangement Test for leukemia and lymphoma was approved by FDA in autumn 1989. It permits the detection of genetic abnormalities associated with certain types of leukemias and lymphomas. Comparable tests are being devised to work in the patient's body, using safe levels of radioactivity or non-radioactive markers.

Biotech may be able to help diagnose colon cancer earlier. Colon cancer is a good example of a cancer readily treatable if detected in time. About 110,000 new cases appear in the United States yearly, 44,000 fatal. Early detection can reduce this toll.

Presently, doctors can locate suspected colon cancers by using barium, administered either through an enema or a "milkshake." Once inside the body, barium usually highlights any tumors on an x-ray.

A more precise method is under investigation. By cloning the antibodies the immune system generates specifically to combat colon cancer, then injecting them into the body, investigators hope to follow them as they rush directly to the cancer site. Because these MAb's are engineered to seek only colon cancer cells, they pass harmlessly from the body if none are present. If they collect at any site, however, they may signal the presence and nature of the colon cancer. Diagnostics taking this approach are in clinical trials.

Devising such tests isn't easy, given the more than 50,000 genes in each cell of the human body. Yet, since the first FDA approval in 1982, development of molecular diagnostics has progressed. In addition to helping analyze the 75,000 new cases diagnosed in the United States annually, the DNA test mentioned above may also be useful in monitoring over 300,000 former patients against a recurrence.

A different lymphoma test is also in early clinical trials. Other diagnostic tests now in development include those for ovarian, liver, breast, and lung cancers.

Working out definitive tests can be frustratingly slow because the development of some cancers is so complex. Certain chemicals can both promote and inhibit tumors, depending on the circumstances, so their presence when detected requires painstaking analysis.

Some monoclonal antibodies go beyond improved detection. For instance, Pap tests are effective in diagnosing early cancer of the uterine cervix, but they cannot distinguish those patients likely to relapse into a more serious form of the disease after surgery. Some 15 to 20 percent of women treated for local cervical cancers fall into this category. French researchers have found that half of cervical cancer patients with high levels of a particular oncogene are disposed to a recurrence of the disease. A MAb test being developed there may help to distinguish such women early on. These women can then be offered more intense alternative treatments than usually required by other patients, hopefully heading off the need for surgery later.

About the Author

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FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.