There are three major modalities for the treatment of cancer:
- radiation, and
Then, there are the following medical specialties that are associated with each of these modalities:
- surgical oncology,
- radiation oncology, and
- medical oncology, respectively.
The concept behind surgical treatment of cancer is very straightforward. If you cut the cancer out of the body, then you can cure the cancer. This, of course, only works for solid tumors such as colon, breast, prostate, and lung cancer. Surgery is not an option for diffuse cancers such as leukemia or lymphoma.
The goal of surgery is to remove every last cell of cancer and while this is easy in theory, in practice it can be very challenging. In order to ensure that all of the cancer has been removed removed, surgeons will attempt to remove a cuff of normal, noncancerous tissue around the tumor called the margin. The larger the margin, the more likely the surgeon is to successfully remove all the cancer. However, the larger the margin, the more damage and side effects the surgery will have on the patient. So the question is always this: How much good, normal tissue are we willing to sacrifice to ensure that the cancer is completely removed?
In some parts of the body, it’s easier to get larger margins because there are less critical structures nearby. In surgical oncology, we can always remove the cancer; the only question is whether the patient will survive the surgery or is able or willing to live with the consequences of the surgery. This is often a very personal decision made between the patient and family and the surgeon. When the cancers are advanced and a large surgery is required, there is wide variation between patients in what they are willing to sacrifice in order to fight the cancer.
Would you be willing to never talk again, or never eat food by mouth again, or see, or hear, or walk, or never have bowel and bladder control? What if losing that sight or ability to walk only gave you a 70% chance of curing the cancer? How about 40%, 20%, 10%? There are no right or wrong answers in these situations and there are also no easy answers. So it becomes extremely important that the patient and the family be appropriately counseled and given the best information to make a decision that is right for them.
Therefore, the “ideal” cancer for surgery is: A small tumor that isn’t nearby any critical organs that can be removed without causing much harm to the patient. Often included in surgery is the removal of the lymph nodes that drain the affected area. The first place that most solid tumors spread to is the lymph nodes, so the lymph nodes around the area are often removed as well. If the cancer is caught early enough, is still small and hasn’t spread, surgery is very effective in most cases. However, as tumors become larger or spread to nearby lymph nodes, surgery becomes less effective at curing the cancer. Once cancers have spread to multiple parts of the body, surgery is no longer effective and is typically not offered as a treatment option.
Radiation has been used as a cancer treatment since the late 1800s when Wilhelm Roentgen first discovered it. Back then, radiation was thought to be a miracle cure for all kinds of medical problems including cancer, tuberculosis, arthritis, mental illness, and fatigue. All kinds of quack cures were sold in the 1920s including radiative bandages, pills, water, and toothpaste. However, it quickly became apparent that radiation was not actually good for people’s health and led to cancers. So then, why do we use something that we know causes cancer, in order to treat cancer? Well, when all of the supposed benefits of radiation were studied, the one that actually turned out to be true was that radiation does indeed kill cancer cells.
Radiation actually can kill all cells and the way it usually causes damage is through damaging the DNA within the cells, which it can do both directly and indirectly by generating highly unstable molecules called “free radicals”. In this way, radiation preferentially kills cells that are rapidly dividing because those cells need to copy their entire DNA with each division, and the rapid turnover of the cells allows less time for the DNA damage caused by the radiation to be repaired. Cancer is even more susceptible to this DNA damage, as cancer cells have defective DNA repair and proofreading mechanisms.
With enough radiation, all cancer cells can be destroyed. However as radiation doses increase, the side effects of the radiation increase exponentially and there is an upper limit at which all human tissue will die and cease to function. Therefore, radiation oncologists have discovered what amount of radiation is needed to destroy most cancers with the least side effects.
Radiation doses are measured in centigray (cGy) or hundreths of a gray. One gray is defined as one joule of radiation per kilogram of tissue and most solid cancers are treated by 60 to 80 cGy while very sensitive cancers like lymphomas can be treated with as little as 20 to 40 cGy.
External beam radiation, where the radiation source is outside the patient and focused in an area in the patient and brachytherapy where radioactive material is implanted into a patient to put the source of radiation directly against the cancer. External beam radiation in most centers are moving to using intensity modulated radiation therapy or IMRT, which is a technologically advanced method of delivering radiation more precisely by using computer modeling and focusing of the radiation beams to target the tumor while reducing radiation to surrounding tissues. This increases dosage to the tumor while minimizing side effects.
Another growing form of external beam radiation in several large cancer centers is proton beam therapy where proton particles, which are actually accelerated matter, are used instead of photons, which are pure energy. Proton beam therapy has the advantage of high precision like IMRT but works by directly damaging the DNA of cells rather than by forming oxygen-free radicals which damage DNA as in photon therapy.
Another form of external beam radiation is radiosurgery where a large dose of radiation is given in one or sometimes several treatments to destroy the tumor. However, radiosurgery destroys all tissue in the target area without discriminating cancer from normal tissue. IMRT and proton therapy are given in smaller doses or “fractions” daily over several weeks to give time for normal tissues to repair the damage while destroying the cancerous tumor.
Side effects of radiation therapy can be minimal or severe depending on the location and dosage of the treatment, and can include dry mouth, dry eyes, stiff and inelastic tissues, cataracts, heart disease, loss of mental acuity, tissue swelling, and cancers.
Conventional chemotherapy is much like radiation therapy in that it relies on chemicals and drugs that cause DNA damage to destroy cancer cells. But unlike radiation, which is focused on a tumor, chemotherapy is given as a pill or an infusion into the entire body. This has advantages and disadvantages. The advantage is that the treatment can go to wherever the cancer is in the body. The disadvantage is that the side effects of the treatment also affect the entire body. For this reason, chemotherapy usually cannot be given at equal doses to radiation therapy because such doses would kill most patients from the severity of the side effects. Radiation therapy can localize the worst side effects to just a part of the body.
Cancers of the blood and leukemias can only be treated with chemotherapy because by definition, they are spread all over the body and radiation or surgery can do nothing for them. Also, certain solid tumors such as lymphomas and certain sarcomas are sensitive to specific chemotherapy regimens and are well treated with them. However, most chemotherapy for solid tumors is usually given as part of a treatment plan that includes either radiation therapy, surgery or both.
The goal of cancer treatment is to kill the cancer without harming the patient. However, all current methods of treating cancer harm the patient to some extent while killing the cancer. If we could figure out what makes the cancer different from normal cells and just aim for that, maybe we could achieve the goal of cancer treatment without side effects. That is the promise of targeted therapy. Much of the research in cancer therapy over the past several decades have been looking for “targets” on cancer cells that we can exploit to kill them while leaving normal cells untouched.
In a few small cases, we have been very successful. One of the first successes was Gleevec, which treats a specific form of cancer called chronic myelogenous leukemia with a very specific mutation in a protein that controls cell division. Gleevec specifically targets the single protein and cures almost 100% of patients with this cancer with minimal side effects. But this miraculous success has not been repeated in other cancers so far. Most other cancers have multiple pathways and most of the proteins that cause the problems in cancers are also found in normal cells, so the differences between normal and cancer cells are very subtle and difficult to exploit.
Nevertheless, there are now several targeted treatments which target proteins involved in cell division, blood vessel formation, cell growth, cell death and hormonal growth. Another form of targeted treatment that is gaining interest recently is a treatment that activates the immune system to destroy the cancer cells.
Common Questions I’ve Heard From Patients
“Doesn’t surgery spread the cancer?”
Surgery that cuts into the tumor can spread the cancer. This is called “tumor seeding” because the broken-off pieces of cancer act like little seeds and can cause multiple new tumors to form in the area of the surgery. That’s why the goal of surgery is to cut around the tumor, in order to avoid this problem. Also, surgery is not known to cause the tumor to spread to areas far from the surgical site (this is called metastasis).
“Isn’t chemotherapy poison?”
Strictly speaking, most conventional chemotherapy is poison in that it can cause harm. They are known to cause DNA damage which is not a good thing, generally. But the benefit of chemotherapy is that it can kill cancer ,which is a pretty important thing. All medicines are poisons in that they can cause harm, but medicines differ from poisons in that they have a benefit, and almost always the benefit is more than the harm. Chemotherapy has much greater harm than most medicines but it also has much greater benefit.
“Doesn’t radiation therapy cause cancer?”
Yes, it can. People that have had radiation therapy have a higher risk of developing certain kinds of cancer several decades after their initial treatment. So why would we give people a treatment for cancer when we know it can cause cancer? Well, the risk is small. For example, if a normal person’s risk of getting a sarcoma is 1 in a million and radiation therapy doubles the risk, that’s only 2 in a million, which isn’t a very high risk (these are numbers given as an example and are not the actual numbers, which vary widely depending on dosage, location and type of cancer). Also, the risk occurs decades later; if people didn’t get treatment for the cancer they already had, they wouldn’t be alive in several decades to even worry about it.
“I’ve heard that X can cure cancer and has no side effects. I want to do that.”
We will discuss alternative cancer therapies in the final part of this series which I’m sure will be very controversial and interesting. If you have any broad questions about cancer and therapy, please comment in the box below and I’ll be happy to update this article with answers.
In Part 1 of this series on cancer, we started the journey to understanding what cancer really is. In Part 2 of this series on cancer, we investigated what causes cancer and how we can reduce our risk. In Part 4, Dr. Lee busts myths about a miracle cure for cancer. In Part 5, you can read about alternative cancer treatments.