Nearing a Cancer Cure? - Medical Myths - Harvard Commentaries

Everyone hopes that someday soon there will be a cure for cancer. Researchers, health care professionals, pharmaceutical companies, and, of course the cancer victims and their families all look forward to the day when a cure for cancer is discovered. There is reason to be optimistic. New approaches that are not only more effective but safer and easier on persons living with cancer are announced often. Statistics generally support the notion that even as advances in early detection identify more cases, advances in treatment have provided improved survival rates and quality of life for many forms of cancer. But if you listen carefully to what experts say when discussing advances in cancer treatment, the word "cure" is rarely spoken or written. There are good reasons for this.

To understand why cancer experts are so circumspect in discussing a cure for the disease, it is important to clarify several misconceptions about cancer:

Cancer is not a single disease. In fact, although there are some common features, cancer is probably hundreds of different diseases. By definition, cancer cells have lost the capacity that normal cells have to control their rate of duplication, and most cancers have an abnormal ability to spread to distant sites. However, each type of cancer could develop, spread, cause illness and respond to treatment in completely different ways. For this reason alone, it is probably inappropriate to even talk about "a cure for cancer" without identifying the specific type and which part of the body is involved.

Prolonged survival is not the same as a cure. The term "cure" suggests that the disease is eliminated from your body and that the episode of illness it caused is over. Yet, even highly effective cancer treatments often cannot guarantee a cure. For example, if colon cancer is detected early and removed surgically before the tumor is large or has spread through the colon wall, 90% of patients will live for at least five years, most of whom will be cured. Yet, it is nearly impossible to identify the 10% who will have a recurrence, and the other 90% cannot be assured of cure until an even more prolonged period of time has passed. That’s why you hear physicians speaking about likelihood, probabilities, and risk factors for treatment response. It’s why you hear much more about "response rates" and "one-, five- or 10-year disease-free survival rates" rather than cure. And it’s also why people who have been treated for cancer — even those with favorable risk profiles — need regular follow-up with their doctors.

For some types of cancer, there is no highly effective treatment. For these, the term "cure" will almost never be used. An example is pancreatic cancer: There are no readily available or effective means of early detection, and by the time the tumor is discovered, it has often spread; while there are occasional exceptions, the term "cure" will rarely if ever be offered as a likely outcome.

For some types of cancer, cure is only known in retrospect. That is, long-term survival without evidence of disease is considered a cure, but until that point is reached, one should not consider that the treatment provided a cure. Unfortunately, there are other types of cancer for which even five-year survival free of cancer is not a guarantee that the tumor has been eliminated. One example of this is melanoma, in which up to 10% to 15% of recurrences are discovered more than five years after initial diagnosis.

The most common forms of cancer affect the skin, lung, colon, breast and prostate. Even among these organs, there are different types, triggers, and responses to treatment. For example, skin cancer includes some dramatically different diseases: carcinoma and squamous-cell carcinoma are the most common but are unique in that they are almost always cured by removal. However, melanoma, another form of skin cancer, is a completely different story. Unless very localized when detected (called melanoma "in situ"), cure rates vary greatly depending on how thick the tumor is, and whether it is confined to the skin, lymph nodes or has spread elsewhere. It is thought that increased sun exposure or depletion of the ozone layer has led to an increased incidence of melanoma. Lung cancer, on the other hand, is strongly linked to a different environmental exposure: smoking. Treatment of newly detected lung cancer has limited effectiveness compared with the potential for prevention of the disease in the first place. Smoking also may increase the risk of pancreatic, bladder and cervical cancer.

Some cancers respond well to chemotherapy, some to radiation, while others require only surgery, and still others require all three modes of treatment. And some very localized tumors require no therapy at all, such as some cases of prostate cancer.

These examples demonstrate some of the many different ways cancer can develop and behave in the body and why they cannot be considered one disease.

There are situations in which optimism is warranted, even when things look grim. As mentioned, some skin cancers and many other types (including colon, breast, lung and prostate) readily respond to treatment when detected early. In these situations, the chance for long-term survival and even cure is good. There are even examples of tumors that have spread to distant areas of the body that may be cured with appropriate treatment. An example of this is testicular cancer — overall, the cure rate is up to 95%, but even when it has spread to the lungs, certain patient subtypes will have up to 90% long-term survival (and presumed cure) with appropriate chemotherapy and surgery.

It is probably best to think about reducing deaths from cancer not as "finding a cure"– in fact, it is likely there will never be a single treatment to cure all cancers. Much more likely is that advances in understanding on a number of fronts will add to what we already know about these diseases, including:

How the various types of cancer develop (including mutations in the cells’ genetic code and how they control cell division)
How cancers can be detected earlier
How to prevent the spread of cancer cells outside of the initial tumor
How to safely and effectively treat tumor cells, including those that have spread outside the initial tumor
How to prevent cancer in the first place

A single treatment may turn out to apply to many types of tumors. For example, the drug imatinib (brand name: Gleevec) was approved in May 2001 as a novel and effective targeted treatment for one form of leukemia, but it has since been approved for several other types of cancer, including certain digestive tumors. In general, however, enough differences exist between different types of tumors to make a single treatment for all cancers unrealistic.

With what we already know about prevention, some argue that our efforts in the fight against cancer are best focused on how to avoid these diseases rather than in how to treat them once present. And even as advances in treatment are realized, an increased emphasis on quality of life and incorporating the preferences of the patient will be critical: It may not be worth extending life for a year or two if the quality of life in those extra years is low.

We all hold out hope for improvements in cancer prevention and treatment, and even for cures. Still, even the most optimistic person should also be realistic: Despite the frequent "breakthroughs" announced on the nightly news, a "cure for cancer" may be a nearly mythical notion, unlikely to be announced any time soon. There’s a good reason that you rarely hear researchers using the words "cancer" and "cure" together. Even so, the advances in cancer treatment you hear or read about are real. But they are generally improvements in therapy, not cures, and apply to one disease at a time.

Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.