Knowing the heterogeneity of every cancer, one might naively have presumed that every patient’s cancer possessed its own sequence of gene mutations and its unique set of mutated genes. But Vogelstein found a strikingly consistent pattern in his colon cancer samples: across many samples and many patients, the transitions in the stages of cancer were paralleled by the same transitions in genetic changes. Cancer cells did not activate or inactivate genes at random. Instead, the shift from a premalignant state to an invasive cancer could precisely be correlated with the activation and inactivation of genes in a strict and stereotypical sequence.
In 1988, in the New England Journal of Medicine, Vogelstein wrote: “The four molecular alterations accumulated in a fashion that paralleled the clinical progression of tumors.” He proposed, “Early in the neoplastic process one colonic cell appears to outgrow its companions to form a small, benign neoplasm. During the growth of [these] cells, a mutation in the ras gene . . . often occurs. Finally, a loss of tumor suppressor genes . . . may be associated with the progression of adenoma to frank carcinoma.”
Since Vogelstein had preselected his list of four genes, he could not enumerate the total number of genes required for the march of cancer. (The technology available in 1988 would not permit such an analysis; he would need to wait two decades before that technology would become available.) But he had proved an important point, that such a discrete genetic march existed. Papanicolaou and Auerbach had described the pathological transition of cancer as a multistep process, starting with premalignancy and marching inexorably toward invasive cancer. Vogelstein showed that the genetic progression of cancer was also a multistep process.
This was a relief. In the decade between 1980 and 1990, proto-oncogenes and tumor suppressor genes had been discovered in such astonishing numbers in the human genome—at last count, about one hundred such genes—that their abundance raised a disturbing question: if the genome was so densely littered with such intemperate genes—genes waiting to push a cell toward cancer as if at the flick of a switch—then why was the human body not exploding with cancer every minute?
Cancer geneticists already knew two answers to this question. First, proto-oncogenes need to be activated through mutations, and mutations are rare events. Second, tumor suppressor genes need to be inactivated, but typically two copies exist of each tumor suppressor gene, and thus two independent mutations are needed to inactivate a tumor suppressor, an even rarer event. Vogelstein provided the third answer. Activating or inactivating any single gene, he postulated, produced only the first steps toward carcinogenesis. Cancer’s march was long and slow and proceeded though many mutations in many genes over many iterations. In genetic terms, our cells were not sitting on the edge of the abyss of cancer. They were dragged toward that abyss in graded, discrete steps.
While Bert Vogelstein was describing the slow march of cancer from one gene mutation to the next, cancer biologists were investigating the functions of these mutations. Cancer gene mutations, they knew, could succinctly be described in two categories: either activations of proto-oncogenes or inactivations of tumor suppressor genes. But although dysregulated cell division is the pathological hallmark of cancer, cancer cells do not merely divide; they migrate through the body, destroy other tissues, invade organs, and colonize distant sites. To understand the full syndrome of cancer, biologists would need to link gene mutations in cancer cells to the complex and multifaceted abnormal behavior of these cells.
Genes encode proteins, and proteins often work like minuscule molecular switches, activating yet other proteins and inactivating others, turning molecular switches “on” and “off” inside a cell. Thus, a conceptual diagram can be drawn for any such protein: protein A turns B on, which turns C on and D off, which turns E on, and so forth. This molecular cascade is termed the signaling pathway for a protein. Such pathways are constantly active in cells, bringing signals in and signals out, thereby allowing a cell to function in its environment.
Proto-oncogenes and tumor suppressor genes, cancer biologists discovered, sit at the hubs of such signaling pathways. Ras, for instance, activates a protein called Mek. Mek in turn activates Erk, which, through several intermediary steps, ultimately accelerates cell division. This cascade of steps, called the Ras-Mek-Erk pathway—is tightly regulated in normal cells, thereby ensuring tightly regulated cell division. In cancer cells, activated “Ras” chronically and permanently activates Mek, which permanently activates Erk, resulting in uncontrolled cell division—pathological mitosis.
But the activated ras pathway (Ras→ Mek → Erk) does not merely cause accelerated cell division; the pathway also intersects with other pathways to enable several other “behaviors” of cancer cells. At Children’s Hospital in Boston in the 1990s, the surgeon-scientist Judah Folkman demonstrated that certain activated signaling pathways within cancer cells, ras among them, could also induce neighboring blood vessels to grow. A tumor could thus “acquire” its own blood supply by insidiously inciting a network of blood vessels around itself and then growing, in grapelike clusters, around those vessels, a phenomenon that Folkman called tumor angiogenesis.
Folkman’s Harvard colleague Stan Korsmeyer found other activated pathways in cancer cells, originating in mutated genes, that also blocked cell death, thus imbuing cancer cells with the capacity to resist death signals. Other pathways allowed cancer cells to acquire motility, the capacity to move from one tissue to another—initiating metastasis. Yet other gene cascades increased cell survival in hostile environments, such that cancer cells traveling through the bloodstream could invade other organs and not be rejected or destroyed in environments not designed for their survival.
Cancer, in short, was not merely genetic in its origin; it was genetic in its entirety. Abnormal genes governed all aspects of cancer’s behavior. Cascades of aberrant signals, originating in mutant genes, fanned out within the cancer cell, promoting survival, accelerating growth, enabling mobility, recruiting blood vessels, enhancing nourishment, drawing oxygen—sustaining cancer’s life.
These gene cascades, notably, were perversions of signaling pathways used by the body under normal circumstances. The “motility genes” activated by cancer cells, for instance, are the very genes that normal cells use when they require movement through the body, such as when immunological cells need to move toward sites of infection. Tumor angiogenesis exploits the same pathways that are used when blood vessels are created to heal wounds. Nothing is invented; nothing is extraneous. Cancer’s life is a recapitulation of the body’s life, its existence a pathological mirror of our own. Susan Sontag warned against overburdening an illness with metaphors. But this is not a metaphor. Down to their innate molecular core, cancer cells are hyperactive, survival-endowed, scrappy, fecund, inventive copies of ourselves.
By the early 1990s, cancer biologists could begin to model the genesis of cancer in terms of molecular changes in genes. To understand that model, let us begin with a normal cell, say a lung cell that resides in the left lung of a forty-year-old fire-safety-equipment installer. One morning in 1968, a minute sliver of asbestos from his equipment wafts through the air and lodges in the vicinity of that cell. His body reacts to the sliver with an inflammation. The cells around the sliver begin to divide furiously, like a minuscule wound trying to heal, and a small clump of cells derived from the original cell arises at the site.
In one cell in that clump an accidental mutation occurs in the ras gene. The mutation creates an activated version of ras. The cell containing the mutant gene is driven to grow more swiftly than its neighbors and creates a clump within the original clump of cells. It is not yet a cancer cell, but a cell in which uncontrolled cell division has partly been unleashed—cancer’s primordial ancestor.
A decade passes. The small collection of ras-mutant cells continues to proliferate, unnoticed, in the far periphery of the lung. The man smokes cigarettes, and a carcinogenic chemical in tar reaches the periphery of the lung and collides with the clump of ras-mutated
cells. A cell in this clump acquires a second mutation in its genes, activating a second oncogene.
Another decade passes. Yet another cell in that secondary mass of cells is caught in the path of an errant X-ray and acquires yet another mutation, this time inactivating a tumor suppressor gene. This mutation has little effect since the cell possesses a second copy of that gene. But in the next year, another mutation inactivates the second copy of the tumor suppressor gene, creating a cell that possesses two activated oncogenes and an inactive tumor suppressor gene.
Now a fatal march is on; an unraveling begins. The cells, now with four mutations, begin to outgrow their brethren. As the cells grow, they acquire additional mutations and they activate pathways, resulting in cells even further adapted for growth and survival. One mutation in the tumor allows it to incite blood vessels to grow; another mutation within this blood-nourished tumor allows the tumor to survive even in areas of the body with low oxygen.
Mutant cells beget cells beget cells. A gene that increases the mobility of the cells is activated in a cell. This cell, having acquired motility, can migrate through the lung tissue and enter the bloodstream. A descendant of this mobile cancer cell acquires the capacity to survive in the bone. This cell, having migrated through the blood, reaches the outer edge of the pelvis, where it begins yet another cycle of survival, selection, and colonization. It represents the first metastasis of a tumor that originated in the lung.
The man is occasionally short of breath. He feels a tingle of pain in the periphery of his lung. Occasionally, he senses something moving under his rib cage when he walks. Another year passes, and the sensations accelerate. The man visits a physician and a CT scan is performed, revealing a rindlike mass wrapped around a bronchus in the lung. A biopsy reveals lung cancer. A surgeon examines the man and the CT scan of the chest and deems the cancer inoperable. Three weeks after that visit, the man returns to the medical clinic complaining of pain in his ribs and his hips. A bone scan reveals metastasis to the pelvis and the ribs.
Intravenous chemotherapy is initiated. The cells in the lung tumor respond. The man soldiers through a punishing regimen of multiple cell-killing drugs. But during the treatment, one cell in the tumor acquires yet another mutation that makes it resistant to the drug used to treat the cancer. Seven months after his initial diagnosis, the tumor relapses all over the body—in the lungs, the bones, the liver. On the morning of October, 17, 2004, deeply narcotized on opiates in a hospital bed in Boston and surrounded by his wife and his children, the man dies of metastatic lung cancer, a sliver of asbestos still lodged in the periphery of his lung. He is seventy-six years old.
I began this as a hypothetical story of cancer. The genes, carcinogens, and the sequence of mutations in this story are all certainly hypothetical. But the body at its center is real. This man was the first patient to die in my care during my fellowship in cancer medicine at Massachusetts General Hospital.
Medicine, I said, begins with storytelling. Patients tell stories to describe illness; doctors tell stories to understand it. Science tells its own story to explain diseases. This story of one cancer’s genesis—of carcinogens causing mutations in internal genes, unleashing cascading pathways in cells that then cycle through mutation, selection, and survival—represents the most cogent outline we have of cancer’s birth.
In the fall of 1999, Robert Weinberg attended a conference on cancer biology in Hawaii. Late one afternoon, he and Douglas Hanahan, another cancer biologist, trekked through the lava beds of the low, black mountains until they found themselves at the mouth of a volcano, staring in. Their conversation was tinged with frustration. For too long, it seemed, cancer had been talked about as if it were a bewildering hodgepodge of chaos. The biological characteristics of tumors were described as so multifarious as to defy any credible organization. There seemed to be no organizing rules.
Yet, Weinberg and Hanahan knew, the discoveries of the prior two decades had suggested deep rules and principles. Biologists looking directly into cancer’s maw now recognized that roiling beneath the incredible heterogeneity of cancer were behaviors, genes, and pathways. In January 2000, a few months after their walk to the volcano’s mouth, Weinberg and Hanahan published an article titled “The Hallmarks of Cancer” to summarize these rules. It was an ambitious and iconic work that marked a return, after nearly a century’s detour, to Boveri’s original notion of a “unitary cause of carcinoma”:
“We discuss . . . rules that govern the transformation of normal human cells into malignant cancers. We suggest that research over the past decades has revealed a small number of molecular, biochemical, and cellular traits—acquired capabilities—shared by most and perhaps all types of human cancer.”
How many “rules,” then, could Weinberg and Hanahan evoke to explain the core behavior of more than a hundred distinct types and subtypes of tumors? The question was audacious in its expansiveness; the answer even more audacious in its economy: six. “We suggest that the vast catalog of cancer cell genotypes is a manifestation of six essential alterations in cell physiology that collectively dictate malignant growth.”
1. Self-sufficiency in growth signals: cancer cells acquire an autonomous drive to proliferate—pathological mitosis—by virtue of the activation of oncogenes such as ras or myc.
2. Insensitivity to growth-inhibitory (antigrowth) signals: cancer cells inactivate tumor suppressor genes, such as retinoblastoma (Rb), that normally inhibit growth
3. Evasion of programmed cell death (apoptosis): cancer cells suppress and inactivate genes and pathways that normally enable cells to die.
4. Limitless replicative potential: cancer cells activate specific gene pathways that render them immortal even after generations of growth.
5. Sustained angiogenesis: cancer cells acquire the capacity to draw out their own supply of blood and blood vessels—tumor angiogenesis.
6. Tissue invasion and metastasis: cancer cells acquire the capacity to migrate to other organs, invade other tissues, and colonize these organs, resulting in their spread throughout the body.
Notably, Weinberg and Hanahan wrote, these six rules were not abstract descriptions of cancer’s behavior. Many of the genes and pathways that enabled each of these six behaviors had concretely been identified—ras, myc, Rb, to name just a few. The task now was to connect this causal understanding of cancer’s deep biology to the quest for its cure:
“Some would argue that the search for the origin and treatment of this disease will continue over the next quarter century in much the same manner as it has in the recent past, by adding further layers of complexity to a scientific literature that is already complex almost beyond measure. But we anticipate otherwise: those researching the cancer problem will be practicing a dramatically different type of science than we have experienced over the past 25 years.”
The mechanistic maturity of cancer science would create a new kind of cancer medicine, Weinberg and Hanahan posited: “With holistic clarity of mechanism, cancer prognosis and treatment will become a rational science, unrecognizable by current practitioners.” Having wandered in the darkness for decades, scientists had finally reached a clearing in their understanding of cancer. Medicine’s task was to continue that journey toward a new therapeutic attack.
* In 1988, the precise identity of only one gene—ras—was known. The other three were suspected human anti-oncogenes, although their identity would only become known later.
PART SIX
THE FRUITS OF
LONG ENDEAVORS
We are really reaping the fruits of our long endeavors.
—Michael Gorman
to Mary Lasker, 1985
The National Cancer Institute, which has overseen American efforts on researching and combating cancers since 1971, should take on an ambitious new goal for the next decade: the development of new drugs that will provide lifelong cures for many, if not all, major cancers. Beating cancer now is a realistic ambition because, at long last, we largely know its tru
e genetic and chemical characteristics.
—James Watson, 2009
The more perfect a power is, the more difficult it is to quell.
—Saint Aquinas, attributed
“No one had labored in vain”
Have you met Jimmy? . . . Jimmy is any one of thousands of children with leukemia or any other form of cancer, from the nation or from around the world.
—Pamphlet for the Jimmy Fund, 1963
In the summer of 1997, a woman named Phyllis Clauson, from Billerica, Massachusetts, posted a letter to the Dana-Farber Cancer Institute. She was writing on behalf of “Jimmy,” Farber’s mascot. It had been nearly fifty years since Jimmy had arrived at Farber’s clinic in Boston from upstate Maine with a diagnosis of lymphoma of the intestines. Like all his ward-mates from the 1950s, Jimmy was presumed long dead.
Not true, Clauson wrote; he was alive and well. Jimmy—Einar Gustafson—was her brother, a truck driver in Maine with three children. For five decades, his family had guarded the knowledge of Jimmy’s identity and his survival. Only Sidney Farber had known; Christmas cards from Farber had arrived each winter, until Farber himself had died in 1973. Every year, for decades, Clauson and her siblings had sent in modest donations to the Jimmy Fund, divulging to no one that the silhouetted face on the solicitation card for contributions was their brother’s. But with the passage of fifty years, Clauson felt she could no longer keep the secret in good conscience. “Jimmy’s story,” she recalled, “had become a story that I could not hold. I knew I had to write the letter while Einar was still alive.”
Clauson’s letter was nearly thrown into the trash. Jimmy “sightings,” like Elvis sightings, were reported often, but rarely taken seriously; all had turned out to be hoaxes. Doctors had informed the Jimmy Fund’s publicity department that the odds of Jimmy’s having survived were nil, and that all claims were to be treated with great skepticism. But Clauson’s letter contained details that could not be waved away. She wrote of listening to the radio in New Sweden, Maine, in the summer of 1948 to tune in to the Ralph Edwards broadcast. She recalled her brother’s midwinter trips to Boston that often took two days, with Jimmy in his baseball uniform lying patiently in the back of a truck.