By Donella Meadows
–March 12, 1992–
Some people say that the discovery of a cancer cure in the Pacific yew is a perfect example of why we should save ancient forests. Some people say environmentalists’ efforts to protect the yew just demonstrate how the Greens care more for trees than for people.
I say that the yew story shows why we should slow down, way down. It took nature billions of years to evolve the yew. It takes a hundred years or so to grow one. It took 30 years of research to turn yew bark into a cancer cure. We’re cutting forests at such a pace that in 30 more years the Pacific yew’s habitat will be essentially gone. Our destruction rate is badly out of synch with nature’s production rate — and our learning rate.
Until a few years ago the Western or Pacific yew was considered worthless and was burned in the slash piles after a logging job. It is one of the slowest-growing trees in the world. It likes the shady, damp understory of old-growth forests of the Northwest. Clearcutting those forests not only destroys yews, it creates sunny, dry conditions that prevent yews from regrowing.
Other species of yew have been used for healing for centuries. The Chinese believe yew contains a remedy for arthritis. In India they use it for rheumatism. The Slishan Indians of Canada take yew for kidney and digestive-tract problems. But it wasn’t until 1962 that the National Cancer Institute (NCI) got around to screening the yew, along with many other plants from the forests of the Pacific Northwest, for its effect on cancer.
In 1963 extracts from yew bark were shown to slow the growth of human cancer cells in tissue culture. In 1964 they proved effective against leukemia in mice. In 1965, with some excitement, scientists began trying to isolate the anti-cancer chemical in yew bark.
The search took three years. By 1968 the active substance was identified and named taxol, after the Latin name of the Pacific yew, Taxus brevifolia. In 1971, almost ten years after the initial screening, chemists figured out the molecular structure of taxol. Unfortunately, it is very complex. It has over 2,000 isomers, which means that the atoms that make it up can be put together into 2,000 different arrangements, only one of which is taxol. Therefore synthesizing the stuff in a lab is tricky. It may never happen in commercial quantities. The delicate chemistry of a yew tree is the one sure way to make taxol.
Purified taxol proved effective against mouse skin cancer in 1974. Preclinical trials were started on human cancer cells grafted onto mice. By the late 1970s taxol had showed strong activity against three more kinds of cancer, including breast cancer. In 1979 a paper was published that began to explain how taxol works. In its presence cells stop dividing. They fill up with a jam of microtubules, which normally form during cell division and then dissolve away again. Taxol somehow prevents their dissolution, and instead of dividing, the cell dies.
In 1980 toxicology studies began, to see how much taxol can be administered to humans safely. In 1982 NCI approved taxol for trials on patients with advanced cancers, for whom all other treatments had failed. Partial remissions were observed. In 1987 NCI ordered 60,000 pounds of yew bark.
By 1988 taxol had produced improvement in 30 percent of patients with advanced ovarian cancer. The following year trials began on breast, cervical, colon, gastric, lung, and prostate cancers. In 1990 tumor shrinkage was observed in 48 percent of patients with metastatic breast cancer. NCI’s 1991 order to the Forest Service was for 750,000 pounds of yew bark, which will take about 150,000 trees.
Under the current protocol one course of taxol for ovarian cancer requires 3 trees. In the United States alone there are 20,000 new cases of ovarian cancer each year, and 150,000 new cases of breast cancer. The Forest Service estimates that there may be 130 million harvestable trees left in Oregon and Washington — if they are no longer trashed and burned on logging sites.
It’s unlikely that yews will be wasted much any more; there’s a yew-peeling scramble going on. Taxol is now worth about $600 a gram; a pound of yew bark is selling for $2-$5 a pound. Yew poaching is becoming a problem.
Last year NCI allocated $1 million to new methods of taxol production. Weyerhaeuser is starting an experimental plantation of yew trees and working on genetic improvements to increase the concentration of taxol. Simpler fractions of taxol are being tested, to see if a more easily synthesized piece of the molecule is medically effective. Other species of yew are under investigation, including the decorative one planted in suburbs everywhere. Scientists are trying tissue culture on yew cambium, trying to extract taxol from needles, trying “semisynthesis” on precursors that may be more abundant in the yew than taxol itself.
Meanwhile the places on earth that produce yew trees in abundance and for free (and spotted owls and thousands of other species) are being destroyed for the short-term profit of a very few people. The tropical forests, where millions of species dwell, are disappearing nearly as fast. Both kinds of forests will be essentially gone within the time it takes to develop just one cancer cure.
If there’s an enemy of people and of trees in this story, it’s not environmentalists. It’s logging companies that operate with a time horizon of two or three years, in a biological and human world that can work only on time scales of decades or centuries.
Copyright Sustainability Institute 1992