Singer Selena Gomez undergoes chemo for lupus, drawing attention to this intervention for autoimmune diseases.

When Selena Gomez announced recently that she had been diagnosed with lupus, many people were shocked to hear the young singer was taking cancer-fighting drugs to treat her condition.

But the use of chemotherapy medications for systemic lupus erythematosus, or SLE, is already familiar to people with this autoimmune disease.

“Every day I take chemotherapy pills and then I get a monthly infusion of a biological drug that has chemotherapy-type side effects such as nausea, vomiting, diarrhea, fatigue, and headache,” 29-year-old Erika Wilberger, of Mechanicsville, Virginia, told Healthline.

While chemotherapy drugs can be used to treat both cancer and lupus, the two conditions are unrelated.

“The biggest thing to understand is that lupus is not cancer,” said Dr. Irene Blanco, an associate professor of clinical medicine at Albert Einstein College of Medicine and a rheumatologist with Montefiore Health System. “There’s a lot of misconception in the community that lupus is cancer because it deals with the immune system and you have abnormal cells.”

As with other autoimmune diseases, lupus causes the immune system to mistakenly attack the body’s own cells. The skin, joints, blood, kidneys, and other organs can all be affected.

Lupus symptoms include arthritis-like joint problems, fatigue, unexplained fever, and rashes on the face and other parts of the body. If organ damage is severe enough, lupus can even be potentially fatal.

Each person’s experience with lupus, though, is unique. They may appear outwardly healthy — making lupus an “invisible illness” — but this condition can profoundly impact a person’s life.

Wilberger, who was married in August, had to postpone her honeymoon due to her condition.

“I was having more frequent fevers, worsening joint and muscle aches, chest pain due to breathing difficulties and fatigue,” she said. “My husband Josh and I decided to do a delayed honeymoon to give my body a chance to recover, so I could fully enjoy our little getaway.”

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Some doctors prescribe cancer-fighting drugs for lupus because they have few other options to slow down an immune system gone haywire.

“The reason why we use these chemotherapeutics is because we don’t have really, really good medicines for lupus,” said Blanco.

Few drugs have been approved by the Food and Drug Administration for treating lupus. Some, such as aspirin and prednisone, are used for a number of other conditions.

One drug approved in 2011 — belimumab, known by the brand name Benlysta — was developed specifically for lupus. Wilberger receives monthly infusions of this medication.

Even with the introduction of this new drug, doctors still have few lupus-specific medications at their disposal. As a result, they have turned to already approved cancer-fighting drugs that target the underlying cause of lupus — a hyperactive immune system.

“What we do is co-opt a lot of medications that suppress the immune system for our purposes in lupus,” said Blanco.

One of the side-effects of many cancer-fighting drugs is that they weaken the immune system. In the treatment of lupus, though, this side effect is the object.

“What we want to do in lupus is bring down the immune system so it stops attacking the patient itself,” said Blanco. “So we use a lot of the [chemotherapy drugs] that suppress the immune system.”

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One chemotherapy drug used to treat lupus and rheumatoid arthritis is methotrexate. Many drugs used to treat one autoimmune disease also work in others because these conditions all share that overactive immune system.

Methotrexate was originally developed to treat cancer. During treatment, this drug may be injected into a vein or put directly into the fluid around the brain.

However, doctors use it much differently when treating lupus and other autoimmune diseases.

“Methotrexate, when it’s given for patients with rheumatologic diseases, is typically given in pill form and given in much, much lower doses — much lower doses,” said Blanco.

And because less of this drug is given to a patient, the effects on the immune system are much smaller.

“In the treatment of cancer, [methotrexate] is a huge immunosuppressant,” said Blanco, but in patients with rheumatologic diseases, “it typically doesn’t suppress the immune system as much as it would for a cancer patient.”

In severe cases of lupus, though, doctors may use chemotherapy drugs more in line with how they are used in fighting cancer.

“If a patient is having neurologic symptoms — where they’re having seizures or stroke or muscular sclerosis-type symptoms — then we’ll tend to use a much stronger, more potent, more aggressive medication that tends to approximate more the effects of the chemotherapeutic,” said Blanco.

Treatments for lupus, though, really depend on which organs are affected and how severely.

“Lupus affects everyone differently and there is no one-size-fits-all treatment,” said Wilberger. “The drugs I take work for me because I have a team of doctors who work hard together to come up with a treatment plan specifically for me.”

This includes several medications to control her lupus — including a high dose of steroids every few months for lupus flare-ups. She also takes drugs to manage related conditions such as breathing problems and to deal with the day-to-day stress of living with a life-threatening illness.

Wilberger admits that taking so many drugs can be overwhelming, but she tries to remind herself how badly she felt before her diagnosis.

“Even though lupus controls most of my life and what I am able to do, I still do my best to remain positive and have hope for the future,” said Wilberger. “Hope is what keeps me alive and fighting even when it all feels so impossible. I refuse to give up without a fight.”

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