The war against an enemy within.

Armed with an arsenal of space-age technology, troops waging the longest, costliest, deadliest war in history are gaining strategic ground against the elusive enemy - cancer.

Since the war on cancer was officially declared by President Richard Nixon in 197 1, the determined forces of science, buttressed by $23 billion in total support, have pushed in a significant, albeit painstakingly slow, advance against the cunning foe.

Grim statistics bear witness to the uncanny ability of cancer (a collective term for more than 100 diseases) to outmaneuver its opponents:

* Cancer occurrences in 1994 (some 1.3 million) topped those of 23 years ago by 18 percent, with the death rate (more than a half million) up 7 percent;

* One in three Americans will likely encounter the potentially deadly adversary at some point in life (8 million are still alive to tell about such an attack);

* By the year 2000, cancer may surpass heart disease as the number I killer in the United States.

Clearly, Nixon erred in his belief that victory would be forthcoming in about eight years - a swift success similar to putting a person on the moon or eradicating polio. As it turns out, cancer presents a far greater challenge.

"We approached the war on cancer like the landing on the moon: if we spend the money, we will solve the problem. We did not appreciate the significant difference between going to the moon and curing cancer," says Dr. Lance Liotta, a leading expert at the National Cancer Institute.

Adds Dr. Drew Pardoll, oncology specialist at Johns Hopkins School of Medicine: "We thought cancer could be cured with the same set of approaches that eliminated the polio scourge, but polio is a simple little virus, while cancer is as complex as the cell. Comparing polio to cancer is like comparing therapy for a wart to therapy for psychosis."

Dr. Patrick Beatty, professor and bone marrow transplant director at the University of Utah Health Sciences Center, says, "We had a tendency to think of cancer as some foreign enemy invading us from the outside, like a virus or bacterium, but it comes from within us and is much too complicated for one magic bullet approach like the polio vaccine."

What we know now. Scientists now know cancer originates with a single normal cell whose genetic machinery goes haywire. Its tightly regulated division process explodes uncontrollably, invading surrounding tissue and setting off a cascade of events that, often 10 or more years later, produce the dreaded diagnosis.

The cell defects - caused by any number of factors, including heredity, viruses, radiation, environment, lifestyle - spell trouble when occurring in three categories of genes: oncogenes, which turn on cell division; tumor-suppressor genes, which switch off the process; and mutator genes, which, when flawed, increase the rates of mutation in the other two groups.

Normally, oncogenes and tumor-suppressor genes work together enabling the body to perform key tasks such as repairing defective cells or replacing dead ones. But defects in these genes can spawn a constellation of tissue mutations that progress to a tumor and, most dangerously, to the advanced stages of metastasis, the lethal spread of the disease through the body. The resolute resilience of the cancer cell has become evident in its astonishing ability to survive all the brute force medicine has been able to muster. Cut out with surgery, poisoned with drugs, burned with radiation, a few cells still all too often manage to survive the onslaught, bide their time, and return, stronger and deadlier than ever.

How can we defeat such a formidable enemy that has survived for thousands of years and whose power grows ever more potent as we age?

Breaking cancer's secret code. The very discovery of the seemingly insurmountable obstacles, made in a stunning series of scientific breakthroughs, has given many of the cancer fighters reason to think the tide is beginning to turn in their favor.

Breaking cancer's secret code (malignancy has been exposed as a genetic disease, the identification of more than I 00 cancer genes) has yielded an unprecedented understanding of how most types of cancer begin, grow, spread, and kill.

"The molecular genetic revolution of the past two decades has pried open the lid on the black box that concealed cancer's innermost secrets," says Raymond White, professor, chair, and director in genetics, cellular, viral, and molecular biology and cancer at Utah.

"Before, we could see what went in the black box, a normal cell, and what came out, cancer, but not what happened inside. Now we have had an incredible revealment of the details of what these molecules are doing inside the box, which points to novel targets for the therapy."

"The war has been successful in the employment of newly available weapons of molecular biology to define what was suspected, but not well characterized - that defects in DNA, the master molecule that encodes the genetic script of life, and changes in genes, are at the fundamental root of tumor initiation," says Dr. Stephen Baylin, professor and tumor biology chief at Johns Hopkins. "We now understand the immense complexity of tumor progression. The number of defects a cell can tolerate is amazing. It helps explain the difficulty in treating cancer. By the time most common types are diagnosed, an astounding array of changes have already occurred."

Making headway. "We have taken a quantum leap in our knowledge base and are faced with the difficult but wonderful dilemma of having to choose from among a wide variety of strategies to treat cancer where none may have existed before," says Dr. Alan Houghton, chief of clinical immunology at Memorial Sloan Kettering Cancer Center. The amassed scientific firepower has forced the enemy's retreat in several skirmishes-and fuels hope for an amlistice within our lifetime.

Some rare though at one time deadly cancers, such as Hodgkin's disease and childhood leukemia, have been defeated and are now considered curable. Half of all patients diagnosed with cancer now can expect to live at least five years, up from 40 percent in the early 1970s and less than 20 percent in the 1930s.

Though not vanquished, some types of malignancies have been turned way back since Nixon threw down the gauntlet against cancer: stomach tumors are down by two thirds, thanks to better diet and food preservation; cervical and uterine cancers are down 70 percent, largely because of early detection through the widely used Pap smear.

While wiping out all cancer remains an elusive goal, scientists are exploring altemative paths to victory. Medicine is moving away from the exclusively strong-arm tactics that have failed to conquer the evasive cancer cell. Doctors are expanding their arsenal to include weapons that subdue rather than slay, an approach that stands to benefit the patient with a prolonged and more pleasant life.

"The limits of what we can do with surgery, radiation, chemotherapy, and even hormone manipulation have been reached. It's time to deal with what we have learned that happens inside the cell," comments Dr. William Goodson 111, surgery professor, University of california at San Francisco. "We are going slowly from cutting, burning, and poisoning the cancer cell to an era in the next decade that will focus on regulating it," adds Dr. Craig Henderson, oncology director at UCSF.

Take breast cancer as an example. "When mammography was introduced in 1973, doctors didn't know that many small, early cancers even existed. Now they know there are many different kinds of breast cancer. And not all of them require a mastectomy, the surgical removal of a breast, which not long ago was standard treatment for all breast cancers.

"We can apply what we have learned about cancer as a genetic disease to diagnosis and treatment, looking for the specific alterations that result in particular tumors and studying how they affect response to particular therapies," says Sheila Taube, cancer diagnosis chief at the NCI. While theoretically any gene that goes awry in a cancer cell offers a target for attack, those that directly influence a cell's decision to divide are attracting particular scientific attention. "Now that we recognize that cancer is a genetic disease, it becomes logical to look for genetic therapies," says, Dr. David Curiel, gene therapy head at the University of Alabama at Birmingham.

Other strategies include vaccines to stimulate the immune system to combat tumors. Vaccines are already saving the lives of patients with melanoma, and specialists believe in the future they may be effective for other types of cancer.

Other teams probing cancer's vulnerabilities are targeting a process of blood-vessel formation called angiogenesis in an attempt to starve the cancer." To grow, thrive and, ultimately metastasize, tumors must attract and become pervaded with a rich supply of blood to provide nourishment and remove wastes. By inhibiting this process, we can annihilate the tumor by choking it from its blood supply," says Dr. David Cheresh, whose team at The Scripps Research Institute in La Jolla, California, has had early success in such efforts.

Such knowledge arms the cancer fighters with a potent weapon but cannot guarantee victory. "Treatment and medical intervention will take us only so far. The best way to cure cancer is to prevent it," says USC prevention expert Leslie Bernstein, whose widely publicized study indicated four hours of exercise a week can substantially reduce the risk of breast cancer in young women.

Thus, while the scientific army can force cancer to retreat on many fronts, the final outcome of the war against the ancient enemy within us will ultimately depend upon us.

Lidia Wasovicz-Pritigle resides in San Rafael, California. She does-freelance writing and is a science writer for United Press International.