Recently, I came across the headline "Scientists Find Achilles' Heel of Cancer Cells", describing the discovery of a histone deactylase (HDAC11) as a novel target for cancer therapies. I was irritated by the metaphor of Achilles' heel, because it implied that this was the lone vulnerability of cancer. I was also embarrassed by the fact that I used the same metaphor for the press release describing our work earlier this year showing that mitochondrial network structure can be targeted in cancer. I decided to google the expressions "Achilles' heel" and "cancer". It turns out that every year, numerous press releases and news articles claim that researchers have finally identified the "Achilles' heel" of cancer. In Greek mythology, Achilles only had two feet and thus two heels; only one of the two heels was vulnerable. So how can it be that hundreds of researchers have found the Achilles' heel of cancer? Apparently, I am not the only one who has used this metaphor inappropriately and it begs the question, whether we should even be using it at all. When I was a child, Gustav Schwab's "Sagen des klassischen Altertums" was one of my favorite books. His gripping narrative of the ancient Greek myths has also been translated from German into English and is available as "Gods and Heroes of Ancient Greece". It was in this book that I first encountered the legend of Achilles and the story of the Trojan War, originally relayed by the Greek poet Homer in his great epic "The Illiad". Achilles was the son of the sea-goddess (nymph) Thetis and King Peleus and was known for his great strength and skills in battle, but I could find nothing heroic in this demigod Achilles. Even though I loved Schwab's narration, I despised Achilles. He vacillated between fits of rage and episodes of prolonged sulking. He was rude, arrogant and violent - Anakin Skywalker on steroids. I was especially horrified by how Achilles tied the body of his enemy Hector to his chariot and dragged it around, in order to humiliate the deceased and inflicting great psychological pain on Hector's family. Basically, Achilles was a jerk; but according to the diagnostic classification of the American Psychiatric Association, Achilles may just have had IED (intermittent explosive disorder). When Achilles was a baby, his mother Thetis stuck him in a special flame to make him invulnerable. She was interrupted by Achilles' father, who was shocked by what he perceived as poor parenting skills shown by Thetis. The interruption prevented Thetis from making her son completely invulnerable, which is why one of Achilles' heels remained vulnerable. Later on in the legend, this vulnerable heel is where the Greek god Apollo directs his arrow and this injury ultimately results in Achilles' demise. I remember the relief I experienced when I first read about Achilles' death. It was karma - he deserved to die, considering all the pain and suffering that he had caused. I also remember that I was confused by the whole invulnerability aspect of the story. In a different part of the legend, his mother Thetis helps him obtain a special armor to protect his body. If nearly all of his body was already invulnerable, why would he need such a special armor? Wouldn't he just need a special kind of Band-Aid to cover his one vulnerable heel? But then again, these were Greek gods and goddesses and they may have had different ways of approaching problems. Perhaps the special armor was extra insurance, just like people whose personal auto insurance covers rental cars but they still get suckered into buying additional rental car insurance at the airport. Later on, I found out the Schwab had combined multiple Achilles legends. The story of Achilles being invulnerable everywhere except for his heel and Achilles' death are not part of Homer's Illiad. It was long after Homer that the heel story became an integral part of the Achilles legend. In one version, Thetis did not place Achilles in a flame but instead dipped him in the magical River Styx. She held him by the heel of his foot, which is why he remained vulnerable in that one area. I am not sure that I would have held my son by the heel of all places, while dipping him into a magical river. Then again, I am not a Greek god. It also begs the question why Thetis did not dip him in a second time to make sure that the previously dry heel now also became invulnerable. In one narration, it was not Apollo who shot the arrow, but the Trojan prince Paris and Apollo merely directed the arrow into Achilles' heel, possibly because Paris was not a very good shot. Even though the heel story and Achilles' death or not part of the Illiad, it is difficult to envision the Achilles legend without it. The idea that even strong, arrogant entities remain vulnerable is very comforting. This may explain why this aspect of the legend is so popular and why it has given rise to the commonly used metaphor of the "Achilles' heel" to describe lone vulnerable spots. Especially when describing cancer, the metaphor seems very apt. One can easily envision a growing tumor as an Achilles - aggressive and apparently invincible. When one identifies a gene or protein that can prevent tumor growth and or even kills the tumor, it is easy to succumb to using the "Achilles' heel" metaphor. The problem with using this metaphor is that Achilles only had one single vulnerable heel. If a researcher claims to have found an Achilles' heel, it not only implies that it is "one" area of vulnerability of the cancer, but that it is the "only" area of vulnerability. Most researchers who work with cancer cells know that there are many different mechanisms by which cancer growth can be slowed down. There is no single vulnerable pathway that can stop all cancer progression. Therefore, when researchers use this expression, they probably just like to convey the image of the powerful Achilles being brought to his knees by a single arrow. They do not want to claim that they have found the ultimate weapon to fight cancer. However, this metaphor inadvertently does imply that the described method is the only way to arrest the tumor. This is not only a gross over-simplification, but plain wrong. Someone who is not familiar with the complexities of cancer biology and reads a press release containing this metaphor may take this to mean that the sole vulnerability of cancer has been identified. Mythology and literature can be very inspiring for scientists and it is tempting to use powerful literary or mythological metaphors when communicating science, but one also needs to think about what these metaphors truly represent. Especially metaphors that oversimplify scientific findings or convey a false sense of certainty should be used avoided. When I think about research, two other Greek legends come to mind: The legend of Sisyphus and the Odyssey. Every day, Sisyphus rolled a rock up a mountain and then had to watch how it would roll back down again. This was his punishment decreed by the Greek gods. It reminds me of a lot of experiments that we scientists perform. When we feel that we are getting close solving a scientific problem we sometimes realize that we have to start all over again. Similarly, Odysseus' long and exhausting journey is also a metaphor that appropriately characterizes a lot of real-life scientific research. Odysseus did not know if and when he would ever reach his destination, and this is how many of us conduct our research. I googled "Odyssey" and "cancer" to see if I could find news articles that allude to the scientific Odyssey of cancer research. To my surprise, I did find a number of articles, but these were not descriptions of scientific "Odysseys". They were reports of cancer patients who described how they had undergone numerous different cancer treatments, often with little improvement. I realize that it is easier to market scientific ideas with a simplistic Achilles metaphor than to point out that science is long-winded and at times disorienting journey, similar to the Odyssey. But if we do want to use metaphors, we should probably use ones that appropriately convey the complexity and beauty of science.