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How Cancer Grows: The Basis of Cancer Treatments
- A fifty-five-year-old man feels a twinge in his back while golfing. The pain persists and begins to pierce his abdomen. Soon after, he is diagnosed with pancreatic cancer and learns that the tumor is too large to be surgically removed. He asks, How could I be so sick and not know it? Does cancer grow overnight?
- A forty-year-old woman with breast cancer undergoes surgery to remove the cancer. Afterward, the surgeon tells her, The surgery went very well, I got all of it. But you should see the oncologist for chemotherapy. The patient asks, Why do I need chemo if I’m cancerfree?
- For four years, a sixty-eight-year-old man with prostate cancer has been receiving hormone treatments that have kept both his cancer and his PSA level (a blood marker of cancer growth) at undetectable levels. Suddenly, the PSA rises and a bone scan shows that the cancer is growing in his bones. He asks, Why did the medicine stop working? How could the cancer move from my prostate to my bones?
- A thirty-eight-year-old woman with lymphoma experiences a complete remission of her cancer after two cycles of chemotherapy. She asks, Why do I need six cycles of chemo if the cancer is already gone?
- A forty-three-year-old woman with metastatic thyroid cancer involving her lungs is referred to another cancer center for a promising experimental treatment. She returns after a year and informs me that she never received any other treatments despite multiple consultations. I immediately order CT scans, which show that the cancer is no longer present. She asks me, How can my cancer just disappear? I reply that it rarely happens and ask if she did anything special to achieve this remarkable result. Prayed a lot and drank a lot of Gatorade, she said laughingly. God and Gatorade, who am I to question that? I replied.
Cancer seems to grow in mysterious ways. It can begin in one location and remain there, or it can spread to other parts of the body. It may grow aggressively from the outset or begin as a slow growth but over time change its stripes and increase rapidly in size. Some cancers remain the same size for long periods, and some can even shrink spontaneously (this is rare except in lymphomas and kidney cancer).
After a successful treatment, cancer may never return and be cured. Alternatively, it may return in the original areas of involvement or in entirely new locations. Again, no two cancer cases behave exactly the same way, and no oncologist has seen every manifestation of every cancer. There are well-described patterns of growth for each cancer type, which is what oncologists are expert at recognizing. But there is a great deal that we do not know about why cancer grows the way it does. For any individual patient with cancer, it is not possible to predict if and when and in which areas the cancer will grow in the body. Yet just as yesterday’s mysteries are common knowledge today, so will today’s questions about cancer yield to the light of ongoing scientific sleuthing. Through advances in cancer research, many of the mysteries of cancer growth are becoming more clearly understood. Paralleling these discoveries are improved ways of treating the disease. How cancer grows and how it is treated are closely intertwined. In this article I explain how cancer grows in the human body and how this knowledge is shaping the development of modern-day cancer therapies.
Cancer Develops over Decades
One of the first questions that every person turned into a cancer patient asks is, When did the cancer start? Anyone diagnosed with cancer naturally wants to know when the disease began, in part to determine if it was caught at its earliest stages but also to try to capture what in their life may have triggered such a revolt in their body.
Most people think of cancer as springing up overnight: one day their body is healthy and the next day there is cancer. They realize that it takes time for the disease to grow to the point of detection, but most think that it begins as a sudden process, an abrupt shock to their healthy cells and tissues. In fact, it is not. Cancers that affect adults usually develop gradually, in stages, and over many years (childhood cancers take less time to develop for a variety of reasons).
The condition that ultimately gets diagnosed as cancer is actually the result of a series of changes to one or a few cells that occurred unnoticed over a decade or more. This incubation period is shorter for those with a personal, family, and/or genetic predisposition to certain cancers, in whom the disease occurs earlier in life. The development of cancer is often a lengthy and drawn-out process that can be divided into two phases: the precancerous phase and the cancerous phase.
During the precancerous phase of its development, the framework for a cancer is laid in the body. Subtle changes occur to a cell that mark it as different from the surrounding normal cells, such as a new shape or loosened attachments to its neighbors. The affected cell will also begin to multiply. Ultimately, the normal anatomy of the region gives way, and a growth will form, such as a polyp in the lining of the colon or an unusual mole on the surface of the skin. These growths are benign (not cancer), but some types are considered to be precancerous-given enough time, a cancer could develop out of them.
One of the earliest descriptions of precancerous changes was made more than forty years ago, when researchers established a link between smoking and lung cancer. Scientists performed a detailed pathologic study of the lungs of both smokers (some of whom died of lung cancer) and nonsmokers that were available through autopsy at several Veterans Health Administration hospitals in the New York area. They found that the lungs of all smokers, in contrast to those of nonsmokers, were pockmarked with abnormal collections of cells, ranging from the simple to the bizarre (the more bizarre the collection, the likelier it is to become a cancer).
Most important, the more a person smoked, the greater the number of abnormal cells found and the higher the likelihood that lung cancer developed. In fact, the lungs of some smokers, including those who did not die from lung cancer, contained carcinoma in-situ; presumably, these individuals would soon have developed lung cancer had they not died of other causes. Today researchers are enrolling active and former smokers in clinical trials testing the use of CT scans and PET scans to detect early lung cancer. The hope is that the disease can be caught before it has spread; final recommendations on screening cannot yet be made. It bears repeating that quitting smoking is the best form of cancer prevention.
A similar progression from precancerous changes to full-blown malignancy has been described for nearly every type of cancer. Precancerous abnormalities and early stage cancers of the mouth and throat, breast, colon, skin, prostate, and cervix can be detected effectively with recommended screening tests, whereas others, such as those of the pancreas and ovary, cannot be detected before cancer develops (promising tests are under development).
I must caution against cancer paranoia and overscreening as a means of early detection. Techniques such as full-body CT scanning to detect any abnormal growth in the body or surgical procedures such as the removal of every unusual mole on the skin have not been validated as useful methods of screening for cancer. If a screening test or procedure has not been shown to save lives, and especially if it involves invasive procedures, then its use should be limited to clinical trials that test its true value.
If the precancerous phase goes undetected, some benign growths will morph into a cancer, and the second phase will take hold. The cancerous phase has been estimated as taking eight years for the average breast cancer, which represents the time required for the first bona fide cancer cell to generate a tumor large enough to be detected (one centimeter, roughly a third of an inch, equal to a billion cells). Although every cancer grows at a different speed, this number gives a rough guide as to the duration of the cancerous phase.
If you are a cancer patient, your awareness of the disease begins with the diagnosis and determination of stage; it continues through the estimation of prognosis and the chances for cure, and it culminates with treatment and being a survivor. Yet all of these aspects of cancer revolve around a disease that has been developing in your body for some time.
It follows then, that when a patient asks me when his or her cancer began, I explain that it likely developed over many years (possibly decades) and in the two phases just described.