Sometimes on The Niche or while teaching students as a professor here at UC Davis School of Medicine, I’ve been asked: What is a teratoma?
Not all tumors are created equal and some like teratomas are particularly unusual.
Exactly what is a teratoma?
Teratomas are germ cell tumors.
What this means is that the cells that gave rise to the tumor in the first place were a powerful stem cell called a “germ cell”. Normally, germ cells make reproductive cells including sperm and eggs. You could think of them as reproductive stem cells. However, sometimes things can go wrong with germ cells such that they don’t do their normal job or end up in the wrong place or both.
Note that teratoma is one of those funny words that can be plural even without adding an “S” at the end so if you wanted to write about 2 such tumors, you could write either “two teratoma” or “two teratomas.”
How do teratoma develop?
During the development of teratoma tumors it is thought that germ cells acquire mutations or other changes.
As a result, instead of making sperm or eggs, the altered germ cells randomly produce a variety of tissues. Sometimes teratoma tumors have a whole array of mature tissue types in them. For instance, when a surgeon or researcher cuts into a teratoma, they may find glands, eye tissue, bone, cartilage and more. A different teratoma from another patient may contain a distinct mix of tissues like digestive glands, skin, sweat glands, and hair. This means that every teratoma is going to be very different and the more precise answer to the question ‘what is a teratoma?’ will depend on the patient and the nature of each tumor.
These different mixtures of tissues and cell types found inside teratomas reflect the power of germ cells to make any cell in the body, which is called pluripotency. Note that totipotent stem cells are slightly different in that they can make any cell in the body plus umbilical cord and placenta too. See my overview of totipotent stem cells here.
Because teratoma are germ cell tumors, they often arise in the locations where you’d find normal germ cells: the testes and ovaries. More rarely they can occur elsewhere in the body and it’s thought that these teratoma occur in part because of germ cells being in the wrong place, perhaps due to a glitch much earlier during embryonic development.
Origins of the name teratoma
Tumors and cancers often have names ending in “oma”. This suffix oma means tumor or cancer.
The “terat” part of the teratoma name comes from the Greek word “teras” meaning monster. So “teratoma” literally means “monster tumor.” It is thought that the name was given because, frankly, teratoma look so disturbing and weird when cut open give the array of tissue types in them, sometimes including teeth.
Teratoma research, beauty in the beast
Teratomas are the subject of many research studies trying to get at a better understanding of why these tumors arise exactly and to define treatments (more below).
Importantly, teratoma are also produced in laboratory stem cell research in rodents. True pluripotent stem cells like IPS cells and hESCs have the power to develop teratoma when implanted subcutaneously in rodents. Hence we have a “teratoma assay” to measure pluripotency.
Research on teratoma production by stem cells provides insights into the properties of the stem cells and also into how teratoma form. In my own lab we have produced teratoma for such studies and you can see examples of stained sections of these teratoma above. While freshly isolated and sliced teratoma look kind of monstrous, when you stain sections they can look quite beautiful as exemplified in the 2 images I’ve included in this post.
What is teratoma treatment? What about prevention?
Fortunately, the vast majority of teratoma are benign tumors. What this means is that unlike aggressive cancers, teratoma often do not invade surrounding tissues and are less likely to cause death in patients.
Teratoma tend to grow as a self-contained roughly spherical or ovoid mass. As a result, teratoma surgery is almost always successful in removing the entire tumor. Surgery is the main form of treatment for benign teratoma.
In less common cases, teratoma-like tumors (sometimes in such cases called teratocarcinoma instead) are or become full-blown cancers, which are much more dangerous. In such cases, the tumor is usually removed as much as possible surgically, followed in some cases by chemotherapy or radiation.
To my knowledge, there is no established way to prevent teratomas.
Prevention of stem cell-derived teratomas
Because differentiated human pluripotent stem cells are being developed as the basis for numerous regenerative medicine therapies, there is concern that residual undifferentiated stem cells could lead to teratoma formation in injected patients, and researchers are working to develop methods to address this concern.
Note: this post is not meant as medical advice. Consult your physician.