What Is Metastatic Cancer, Exactly?

Everything you need to know about how cancer spreads.

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More than 90 percent of deaths directly or indirectly caused by cancer don’t come from the original tumor—they’re caused by cancer that’s spread to other parts of the body, known as metastatic, or stage IV cancer.

Stage IV cancer is particularly serious because it tends to target vital organs. At these new sites, tumor cells act differently, making therapies less effective. The goal of treatment often turns from curing to moderating, but survivors could still live for years, says Marleen Meyers, MD, medical oncologist at the NYU Langone Perlmutter Cancer Center. “It doesn’t mean they’re going to die imminently or have a short life expectancy—it just means treatment isn’t for curative intent but to alleviate symptoms or prolong life,” says Dr. Meyers. “Metastatic cancer is not a death sentence.”

The idea of stopping cancer from spreading would be to fight a losing battle, says Danny Welch, PhD, director of the National Foundation for Cancer Research Center for Metastasis Research. “Various labs have shown cancer can start having cells spread before the tumor is even large enough to detect,” he says. “But the good news is, millions of cancer start the process of spreading, but very few grow into real metastasis.”

For a new tumor to form, a couple things have to happen. First, the cancer has to be invasive. “That means the cells had to get out of the original site and burrow a little deeper to have access to blood vessels or lymph nodes,” says Dr. Meyers. The more aggressive an individual tumor is, the more likely it is to spread.

Once the cancer starts to travel, it can land almost anywhere. But a tumor won’t form unless the area creates new blood vessels that create a good environment where it can live. “If you think of tumor cells as seed and tissue as the soil, if you don’t have the right kind of soil and the right kind of seed, they don’t grow,” says Dr. Welch.

Depending on the type of cancer, a tumor will be more attracted to some spots over others, says Dr. Welch. “Every tissue secretes molecules like perfume,” he says. “Certain tissues have a ‘come hither’ scent to them that tumor cells recognize, and others say ‘ew, skunk’ and avoid those.” For instance, certain lung cancers frequently spread to the brain, while some breast and prostate cancers are most likely to travel to the bone.

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After a new tumor starts to form, a survivor could start feeling a general burden from the cancer with symptoms such as fatigue and fever. The site of the new tumor could also cause symptoms—for instance jaundice and poor appetite from the liver, pain near the spot in the bone, and weight loss despite normal eating from the digestive system.

Some cancers are more likely to spread than others. For example, brain cancer has a low chance of becoming metastatic, while the majority of pancreatic cancers will travel to another site. “Some of it has to do with the aggressiveness of the cell type, some of it has to do with the ability to find the cancer when it’s early enough to cure it,” says Dr. Meyers.

Doctors will screen some patients, like people treated for certain lymphomas, frequently because there’s a high recurrence rate, but it’s also easy to treat if it does come back. But other types, such as brain cancer, aren’t screened as often, because survival rates are the same, whether the cancer is found from a routine scan or after waiting for symptoms, says Dr. Meyers. Screenings can also find false positives, meaning it looks like the cancer has spread when it hasn’t. “If it turns out to be negative, putting people through that and the anxiety without a survival difference doesn’t make sense,” says Dr. Meyers.

Advancements in treatments have developed good ways of preventing cancer from spreading. Even if there aren’t any signs of metastasis after the cancer is removed, doctors might give chemo, hormone therapy, or even drugs to remove the few, tiny cells that are too small to be seen. Click here to find out what oncologists do to avoid cancer.

Even though stage IV has spread to another area of the body, it is often treated the same way the primary cancer would be. But rather than targeting a certain spot, the therapy becomes systemic, treating the entire body. “Once somebody does surgery, all the other therapies are designed to mop up cancer cells that have moved elsewhere in the body,” says Dr. Welch. “Once the cancer has spread, we have to start treating the whole body.”

Advancements in treatments are helping metastatic cancer survivors live longer than before. “The thing they need the most is for other people not to look at them as to be pitied and that they’re going to die immediately,” says Dr. Welch. “I talk to a lot of patients with metastatic disease, and they’re fighting for their lives and actually doing pretty darn well for quite a while. It’s not where it needs to be—certainly not good—but it’s certainly better than giving somebody no hope.”

MORE: 21 Completely Reassuring Things Scientists Wish You Knew About Cancer

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Originally Published in Reader's Digest