As I’ve mentioned in the introductions to the other “cancer awareness month” posts that I’ve written, I believe very strongly that even though I identify myself as primarily a breast cancer advocate, it is important for me to have some level of understanding of the other major cancer types. To help broaden my knowledge, I’ve been using the various cancer awareness observances as my guide for which cancers to research and write about. And as it turns out, there are A LOT of them in September. Over the course of the last few weeks, I’ve written posts touching on Childhood Cancer Awareness Month, Blood Cancers Awareness Month, Ovarian and Gynecological Cancers Awareness Month, and Prostate Cancer Awareness Month. Today, to wrap things up, I’m going to write a little bit about thyroid cancer in honor of Thyroid Cancer Awareness Month.
Thyroid Cancer Awareness Month was first initiated by ThyCa: Thyroid Cancer Survivors Association back in 2000. When it was originally founded, it was only a week long observance that was extended for the full month of September in 2003. As ThyCa puts it on their website:
Thyroid Cancer Awareness Month promotes thyroid cancer awareness for early detection, as well as care based on expert standards and increased research to achieve cures for all thyroid cancer.
In my reading, I came across some assertions that due its relatively low mortality rates, thyroid cancer was the “good” cancer to get. Well, that’s just ridiculous. All cancer sucks because all cancer can and does kill people. There is no such thing as a “good” cancer to get. And with the fastest increasing incidence rate of all cancers in both men and women, it’s time to pay more attention to thyroid cancer!
About Thyroid Cancer
Thyroid cancer, following the traditional naming conventions in oncology, is any cancer that forms in the thyroid gland. That part should be pretty straightforward by now. But what exactly is the thyroid gland? Well, the thyroid gland is a small organ at the base of the throat, just below the larynx (voice box) that makes hormones to regulate the rate of metabolism. The thyroid is shaped sort of like a butterfly, with two larger lobes connected by a small piece of tissue called the isthmus. In healthy individuals, the thyroid is a little larger than a quarter and can’t be felt manually through the skin. The thyroid is composed of two primary hormone producing cells:
- Follicular cells, which use iodine from the blood to make the not so creatively named thyroid hormone (TH). TH is produced in response to increasing levels of the also not so creatively named thyroid stimulating hormone (TSH), which is generated and released from the pituitary gland. Because TH is required for metabolism, improper levels of TH can have a whole host of side effects. Someone who has too much TH (called hyperthyroidism), for example, often experiences irregular heartbeat, trouble sleeping, nervousness, hunger, weight loss, and feeling to warm. Having too little TH (which is called hypothyroidism), on the other hand, can cause a person to feel slow and fatigued and to gain weight.
- C cells, or parafollicular cells as their also called, which are responsible for producing calcitonin, a hormone that helps regulate how the thyroid uses calcium.
Thyroid cancer can develop in either thyroid cell type, giving rise to four major subtypes of thyroid cancers: papillary carcinoma, follicular carcinoma, medullary thyroid cancer, and anaplastic thyroid cancer. Let’s go through each one, one at a time.
The most common subtype of thyroid cancer is papillary carcinoma, which develops from the follicular cells. Because these are glandular cells, this type of thyroid cancer is also sometimes referred to as papillary adenocarcinoma. Papillary carcinomas, which account for 86% of all thyroid cancers, are generally slow growing, although they are prone to spreading into the lymph nodes of the neck. These cancers are usually isolated to only one lobe of the thyroid, although not always. Papillary carcinomas can usually be treated and are rarely fatal.
The second most common subtype of thyroid cancer is follicular carcinoma, which accounts for 9% of all thyroid cancer diagnoses. Follicular thyroid cancer is very similar to papillary thyroid cancer in that both types of cancer originate in the follicular cells and are relatively slow growing. However, unlike papillary thyroid cancer, follicular thyroid cancer generally doesn’t spread to the lymph nodes. Follicular thyroid cancer is most common in countries lacking dietary iodine. The prognosis for individuals diagnosed with follicular thyroid cancer is generally good, although not quite as strong as for those with papillary carcinoma. This is at least in part due to the relatively poor prognosis for the Hürthle cell carcinoma subtype of follicular cancer. Because Hürthle cell follicular carcinomas do not readily absorb radioactive iodine, they are often diagnosed at later stages and are much more difficult treat.
The third major subtype of thyroid cancer is medullary thyroid cancer, or MTC. Unlike the previous two subtypes, MTC develops from the c-cells of the thyroid. MTC, which accounts for 2% of all thyroid cancers, often results in abnormally high levels of calcitonin. MTC is usually slow growing and is treatable if caught before the cancer spreads to other parts of the body. MTCs can be linked to inherited mutations in the RET. This form of MTC, which I’m going to talk about more later in this post, is known as familial medullary thyroid cancer and accounts for 25% of all MTCs.
The most rare form of thyroid cancer is anaplastic thyroid cancer, which accounts for approximately 1% of all thyroid cancers. Anaplastic thyroid cancer also develops in the follicular cells, and is thought to sometimes develop from an existing papillary or follicular cancer. Because anaplastic cancer cells are highly dysmorphic and do not resemble healthy thyroid cells when examined under a microscope, anaplastic thyroid cancer is sometimes described as “undifferentiated” thyroid cancer. Anaplastic thyroid cancer is the most aggressive form of thyroid cancer, rapidly invaded the neck and then spreading to other parts of the body. Because of this, anaplastic thyroid cancer is relatively hard to treat.
Finally, while it is not technically a form of thyroid cancer, I wanted to just briefly write about parathyroid cancer, which is any cancer that develops from the four tiny parathyroid glands located at the back of the thyroid. Parathyroid cancer is very rare (with less than 100 cases occurring in the US each year) and generally results in elevated levels of calcium in the blood due to calcium dysregulation. Parathyroid cancer is much more difficult to cure than thyroid cancer.
While the cause of every form of thyroid cancer remains unknown, there have been a handful of risk factors that have been identified. For as yet unknown reasons, thyroid cancer is three times more common in women than in men. Moreover, women tend to be diagnosed with thyroid cancer at a younger age, with the peak rate of diagnosis for women occurring in their 40s and 50s while the peak rate of diagnosis occurring in their 60s and 70s. Eating a diet that is low in iodine has also been shown to increase the risk of developing thyroid cancer, although due to dietary supplements like iodized table salt, this isn’t generally a concern here in the US. While exposure to radiation can increase your risk of developing cancer in general, radiation exposure seems to be particularly strongly linked to an increased risk for thyroid cancer. This includes both exposure to medical radiation as a child and nuclear fall out from living near atomic bomb testing sites and disasters such as the meltdown of the Chernobyl nuclear power station. Finally, there have been a number of genetic mutations linked to the various subtypes of thyroid cancer, which I’m going to talk about in the next section.
The Genetics of Thyroid Cancer
There are two primary types of genes that, when mutated, can result in cancer:
- Oncogenes: These are genes that promote growth and cell division. These types of genes are usually turned “off” and are only switched on under highly regulated circumstances. When an oncogene becomes mutated, it becomes permanently turned on (and in some cases turned way up!), resulting in uncontrolled cell growth and division.
- Tumor suppressor genes: These are genes that are normally responsible for turning off the oncogenes and stopping cell growth and division before it gets out of control. When tumor suppressor genes become mutated, the off switch essentially is broken, allowing cells to continue growing and multiplying. The rate of cell growth and division isn’t higher, it’s just that the stop light is busted. As a result, mutations in tumor suppressor genes generally result in less aggressive forms of cancer.
Different cell types in the body seem to have certain genes that are more vulnerable to cancer-causing mutations than others. These mutations can be either inherited (meaning you were born with a bum form of the gene) or acquired (meaning you picked up that damage at some point during your life). Cancer due to inherited mutations is known as familial cancer and cancer that is due to acquired mutations is known as sporadic cancer. One of the great challenges in cancer research, then, is to identify both the vulnerable genes associated with each cell type (and therefore associated with each cancer type) and to identify the source of the mutations in those genes. In the case of thyroid cancer, and especially MTC, we actually have uncovered the answers to a few of these genetic questions.
The primary gene that has been associated with thyroid cancer is the gene RET. The mutated form of RET is the oncogene PTC. Acquired mutations in RET have been found to play a role in some papillary thyroid cancers as well as in approximately 10% of sporadic MTCs. Inherited mutations in RET, though, underly almost all cases of familial MTC. Nearly everyone who inherits a mutated form of RET ultimately develops MTC. As a result, if someone has a strong family history of MTC, many doctors will recommend genetic testing and potentially prophylactic removal of the thyroid as a means of preventing thyroid cancer.
Other oncogenes that have been associated with thyroid cancers include:
- BRAF (oncogene) – mutations in BRAF have been associated with 30-70% of papillary thyroid cancers
- NTRK1, MET (oncogenes) – less common than BRAF mutations, mutations in these two genes have also been linked to papillary thyroid cancer
- RAS (oncogene) – mutations in RAS have been linked to follicular thyroid cancer
- p53 (tumor suppressor gene), CTNNB1 – mutations in these two genes have been linked to anaplastic thyroid cancer.
Hands down, the most important breakthrough in cancer research has been the recognition that cancer is ultimately a disease caused by genetic mutations. While we still have a lot of questions still to answer when it comes to the genetics of cancer, seeing how far we’ve come in understanding the genetic basis of thyroid cancer gives me hope that those elusive answers for all cancers are closer to being discovered than ever before.
It is estimated that 56,460 people will be diagnosed with prostate cancer in 2012, with 43,210 of those diagnoses occurring in women. 1780 people will die of thyroid cancer in that same time period. 97.5% of all people diagnosed with thyroid cancer live at least five years following initial diagnosis. One in 97 people will be diagnosed with thyroid cancer at some point in their lifetimes. The NCI allocated $16.2 million (or 0.32%) of their budget for thyroid cancer research in 2011, the most recent year for which those statistics were available.
If you would like to learn more about thyroid cancer, I highly recommend reading through the NCI’s web pages dedicated to thyroid cancers, which can be found here. Their “snapshot” report on thyroid cancer is particularly informative, especially the section discussing recent research investments and findings. I also found the American Cancer Society’s Learn About Cancer: Thyroid Cancer section to be very useful. All of the statistics cited in the post were from the Surveillance Epidemiology and End Results (SEER) fact sheet on thyroid cancer, which can be found here. These webpages were my primary sources of information for this blog post.
The American Association for Cancer Research recommends ThyCa: Thyroid Cancer Survivors’ Association for additional thyroid cancer advocacy and patient support information. I also recommend the Light of Life Foundation for more information about thyroid cancer in general and to learn how you can get more involved in advocating for thyroid cancer research.
As with all of these cancer awareness posts, I hope that everyone reading this found it helpful and informative. I know I learned a lot researching it and will be a more effective cancer advocate for it!
Note: While I am a biomedical scientist, I am not considered an expert (medical or otherwise) on thyroid cancer. This post, as with all of my “awareness month” posts, is not meant to be an in depth review of thyroid cancer. Rather, I only wanted to provide a brief overview of thyroid cancer in order to help further the larger cancer community’s awareness of this common cancer. Moreover, while I provided links to a number of thyroid cancer organizations at the end of this post, I have not researched these organizations to the extent that I do for my “Spotlight On” series of posts. Until I can research them further, I am not explicitly advocating financial donations to these organizations (although I certainly won’t advise you against it either should you find them worthy!). Instead, I am recommending them here because each organization is a well respected leader in these specific areas and is considered a reputable source for further information on thyroid cancer.