Dealing with cancer is no small task. From the initial diagnosis to gruelling treatment regimens, there’s a reason the whole thing is often referred to as a “battle”. But you’d hope that when the battle is won, things can go back to normal. Unfortunately, for many, it doesn’t. In fact, up to 83% of patients experience lasting effects, including fatigue, increased risk of secondary cancer, permanent pain, lymphedema, and many more. What makes this rather frustrating is that many of these effects come from the treatment itself, not the disease. To treat something as difficult as cancer, we use methods that can be rough on the body. On top of that, many of the treatments we use aren’t specific to cancer itself. Surgery, radiation, and chemotherapy all damage healthy cells too. Unfortunately, these treatments are necessary to get rid of something as dangerous as cancer. So, today, we’re going to talk about some of the lasting effects of cancer and cancer treatment, including what they are, and why they happen.

A secondary cancer is the development of an entirely new cancer in someone who’s already been diagnosed. Secondary cancers are unrelated to the first, meaning that they’re different than a primary cancer spreading to a new organ. Some treatments that are commonly used can actually increase one’s risk for secondary cancers. The idea that treating one cancer can increase the risk of another is rather daunting, but sometimes that risk is necessary. In the case of radiation and chemotherapy, that risk is largely unavoidable. Luckily, the risk of developing new cancers as a result of radiation and chemotherapy is relatively low.

Chemotherapy and radiation therapy are incredibly tough on your cells, cancerous or otherwise. Both treatments kill cancer by damaging its DNA. When a cell’s DNA is damaged, it only has a few options. It can repair the DNA, which is challenging if a cell has too much damage. It can enter a dormant state, where it no longer divides. And finally, a cell can simply die. Unfortunately, these DNA-damaging treatments can also damage healthy cells. Which means that, because the mutations caused by treatments are random, they can actually lead to cancer-causing mutations in healthy cells. Luckily, this is rare, and a single healthy cell would have to accumulate multiple of these mutations, which is why the risk of secondary cancers remains low. But, it isn’t nothing.

The hormonal rabbit hole goes rather deep. Hormones play a role in many important processes in our body, including our sleep, emotions, and physical health. So, it’s no surprise that hormonal imbalances caused by cancer treatment can lead to so many different issues. Just as examples of some of the issues caused by hormonal imbalance, we have hair loss, dry skin, cramps, anxiety, depression, weight gain, changes in sex drive, and even bone loss.

So, why do they happen? Well, there are a few different reasons. In some cases, it’s because the treatment itself directly targets hormones. That’s because some cancers use hormonal signals to promote their growth. These are called hormone-sensitive or hormone-dependent cancers. The most common types are breast and prostate cancer. One common therapeutic approach for these cancers is to block hormone signalling in one way or another. In doing so, you also impact hormonal levels throughout the entire body, leading to off-target effects like those previously mentioned. In other cases, it’s caused by damage to hormone-producing organs, like the thyroid gland, ovaries, or testes. That could include radiation therapy, surgery, or chemotherapy. In all cases, unintended damage to these glands can impair their ability to produce hormones.

To understand lymphedema, we first need to understand the lymphatic system. Just like the circulatory system that carries our blood, the lymphatic system is a collection of vessels that carries lymph and returns it to the blood. Lymph is a clear fluid in our body’s tissues. It carries waste and debris from our cells, carries hormones and nutrients, and transports immune cells around the body. Extra lymph is collected in the lymphatic vessels or nodes and is returned to the blood. Lymphedema is a condition caused by failure to drain lymph from a certain area. Often occurring in limbs, it can cause swelling and pain, and currently has no cure.

In terms of how cancer treatment leads to lymphedema, it’s straightforward. Just as certain treatments can damage glands that produce hormones, they can damage lymphatic tissues too. If a lymphatic vessel is damaged during treatment, either by surgery or radiation therapy, it can lose its function. Sometimes, lymph nodes or vessels are specifically removed if they contain cancer cells. If these vessels are damaged, they can’t carry lymph out of that tissue, so it builds up, eventually leading to lymphedema.

As much as one might hope things would return to normal after cancer treatment, it’s often not the case. In fact, many patients continue to experience symptoms once treatment stops. These symptoms can vary greatly, from fatigue and emotional burdens to physical impairment, all of which can have severe impacts on someone’s quality of life. This is the unfortunate risk of treating cancer: treatment will likely have lasting impacts on someone’s life. That’s precisely why doctors weigh those risks carefully, consider the consequences, and make sure the benefits outweigh them. It’s also why there’s infrastructure in place for continued care of cancer survivors. As a result, the research going into improving treatments focuses on better treatment efficiency, but also reducing off-target effects and accidental damage. It’s also crucial to continue researching the lasting effects themselves. Many are incurable, difficult to treat, or we simply don’t understand them. So, continuing to research and understand them could help improve outcomes for patients, even after treatment stops.

I hope you learned a little something this week, but next week we’re going to talk about some of the models used to study cancer in labs.

See you next week!

If you missed last week’s letter, you can read “Mighty Microbes” to learn a little more about the role of microbes in cancer.