More and more research is taking place on the risk of Secondary cancer risk in the radiation oncology communities. This is because the treatment we are delivering these days have much higher chance of survival than in decades before. Patients are living longer, and therefore may get a cancer that could have been introduced from the radiotherapy itself.


Radiation Induced Secondary Cancers


What are radiation induced secondary cancers?


Radiation induced secondary cancers are cancers which have formed due to a patient having radiotherapy for the treatment of a primary cancer.


Radiation is a double edged sword. As we explain in DNA damage and repair it can  both cure cancers, but the same curing ability can cause cancers to form. If the radiation is correctly directed to the tumor, it will kill the tumor cells and cure the patient of cancer.


But as the radiation often has to travel through healthy tissue before reaching the tumor, it will damage some of the healthy cells along the way. There is a small chance that this radiation will damage the DNA of a cell, but not kill the cell. This mutation of the DNA can eventually lead into cancer.

What are Secondary Cancer from Radiotherapy


The idea of radiation induced secondary cancers is somewhat controversial. There is limited data to prove it exists, or to prove it does not exist for adult cancer patients. It has long been proven for children and young adults. But it is much harder to get good data for adults.


There are a few reasons for that. First off, it takes roughly 10 or more years for a secondary cancer to form. Now for young adults and children it is easy to provide secondary cancer risk, as most, if not all, will still be around 10, 20, 30, or even more than 50 years after their treatment.


But for adult patients, the numbers drop of after 10, 20, and 30 years after treatment. And this is not only due to complications from the treatment. Rather, some may dies from natural causes, or from other diseases.


The other issue with adult patients is that their risk of getting a cancer is significantly higher than for children. Therefore, you need to determine if the cancer has occurred naturally, or in fact was induced from the radiotherapy.


The final hurdle that researchers have to overcome it to formulate a better understanding of the complex biological processes involved in inducing cancer from radiation. The biology is currently not fully understood. Several advances in molecular biology are still needed.


One area of understanding that has improved greatly over the last decade is the ability to identify genomic characteristics of certain sub populations. Some of these genomic characteristics increase a certain sub-populations risk to inducing secondary cancer from radiotherapy. Therefore, if we know a patient’s belongs to this sub-population risk group extra measures can be incorporated. Such as an increased scanning rate to catch any secondary cancers earlier.


All this means it is hard to get good certain data for adults on the risk of secondary cancers from the treatment.


As always, the radiotherapy community is on the conservative side, and assumes that it does exist for adult patients. That radiotherapy probably does increase the risk of a secondary cancer somewhat.

People are Generally Living Longer


Populations are living longer. This has been the trend for as long as I can remember. With an increasing life expectancy comes an increasing rate of cancer cases. People get older and the incidence of cancer increases. With more and more of these patients receiving radiation to cure their cancers the more people are exposed to the risk of secondary induced radiation therapy cancers.


And with the improvement of radiotherapy technology, the 5 year survival rate of all cancers is steadily improving. Patients are routinely surviving well past 5 years. The late side effects of radiotherapy have become more of a relevant concern than previously thought.


It is more important than ever for clinicians and doctors to have an accurate risk estimation on the rate of secondary cancer after radiotherapy.


Risk factors for Secondary Induced Radiation Cancer


So what are the risk factors of secondary cancers after radiation? And how is the radiotherapy profession trying to minimize this risk without compromising patients treatments cure rates?

At the time of treatment, there are a number of factors that can increase or decrease the risk of secondary induced radiation therapy cancers. These include; the age of the patients, the patients genetic risk factors, and the side of the treatment.


Patient’s Age Risk Factors


There is significant research showing that one of the most important risk factors for developing a secondary radiation induced cancer is the age of the patient at the time of radiotherapy. This makes sense, the younger you are, the more time you will have to develope the secondary cancer.


The younger the patient, the higher the risk of a second cancer


The data that the radiotherapy community have use to prove that young patients are more at risk come from two main sources. One is from studying atomic bomb survivors, and a second is a large study of childhood cancers.

Risk Estimate for Secondary Cancer from Radiotherapy


The above it a graph showing the estimate secondary cancer risk from radiation. This is a ballpark estimate from the findings of the study. The first of the findings was that the risk of a second cancer for pediatric cancer patients is around 7.9%. The second finding was that the relative risk decreased by roughly 17% for each decade increase of age at the time of treatment. From this you can get a very rough estimate of the risk.


A 10 year old patient is probably twice as likely to develop a secondary cancer compared to a 40 year old patient. And four times as likely as a 70 year old patient.


Patients Genetics Risk Factors


You must of heard of the BRCA1/BRCA2 mutation by now. It’s a gene mutation that increases the chance of developing breast cancer. People with this gene mutation are at a higher risk of developing secondary induced radiation therapy cancers.


But if we know that a patient has these genes, we can increase the monitoring and catch any new cancer early. This give a much higher chance of curing the secondary cancer. Catching any cancer early greatly improves the ability to cure it.


With the rapid increase in molecular genomics, it is expected we will find other genetic identifiers than can be used to predict at how much risk a certain person is. While not decreasing the rate of secondary cancers, this will increase the chance of catching any secondary cancer earlier through monitoring of higher risk group patients.


Treatment Site Risk Factors


The chance of developing a secondary cancer is also linked to where the original treatment was. There is evidence to link treatment of Hodgkin’s lymphoma and an increased risk of breast cancer and sarcomas.


But again, knowing this fact doctors know to keep a closer surveillance on these patients.


Another side that has linked secondary cancers is prostate radiation therapy. Prostate radiotherapy has be linked to tumors in the bladder and rectum. This makes sense as these organs are very nearby the prostate and will receive radiation during the treatment.


Other sites on the other hand have no increase in developing secondary cancers after radiotherapy. The one notable treatment is cervical cancer, which showed no increase risk at all. This shows us that the treatment location is important in determining the risks of secondary cancers.


Radiotherapy Technology is Evolving


Another problem in identifying the risks is that radiation therapy technology is improving all the time. The changing technology changes the amount of radiation received by different organs at risk.

The general change has been from larger radiation doses received by a few of the surrounding organs, to lower doses received by many of the surrounding organs. This is know as the low dose bath. Since many organs can tolerate this low dose bath, the side effects during treatment have decreased remarkably over the last few dedicated.


It could be argued that the risk of developing a secondary cancer from radiation therapy should also decrease, similar to the decrease in side effects from the low dose bath.  But the evidence is not clear yet. We will have to wait before this can be proven.


Others argue that since more tissue is irradiated to a lower dose the risk of secondary cancer will be increased compare to the older style of treatments. Either way, the newer treatments have far less side effects than the treatment before them. Which is a great achievement.


Final Thoughts


Developing a secondary cancer from a treatment supposed to cure cancer is not a great thing. But you have to remember that many of these patients would have died without the original treatment. Giving these patients another decade or two is far better, even if they are at an increased risk of developing a secondary cancer.


Understanding the risk factors will allow doctors to catch the secondary cancer earlier, improve treatment techniques and make improved treatment decisions that will benefit the cancer patients.


We will have to wait for more data to come in for some of the newer style treatments, but overtime radiotherapy treatments will improve from scientific research, as they have always done.