Side Effects From Breast Cancer Treatments

Medically Reviewed by Brunilda Nazario, MD on October 24, 2023
9 min read

Nonsurgical breast cancer treatments aim to destroy cancer cells. These treatments include:

  • Chemotherapy
  • Radiation
  • Hormone therapies
  • Immunotherapies (sometimes called biological therapies)
  • Targeted therapies

But most of these treatments don't affect just cancer cells. They also can affect healthy cells and can change how you feel. This could cause a number of side effects including:

  • Loss of appetite
  • Nausea and vomiting
  • Weakness and fatigue
  • Mouth sores or dry mouth
  • Taste changes from cancer or chemo treatments
  • Hair loss
  • Weight gain
  • Early menopause
  • A higher risk of infections
  • Bleeding
  • Diarrhea

Medications and other therapies that address these effects can help ease many of these side effects.

Radiation, chemo, immunotherapy, some hormonal therapies, and even some pain meds can make you less hungry and lead to loss of appetite or taste, all of which can make it hard to get the nutrition you need. Try these tips to make sure you’re eating a healthy diet:

  • Eat a few small meals during the day instead of three large ones.
  • Try an "instant breakfast" mix or other nutritional shakes between meals.
  • Eat your largest meal of the day when you are most hungry.
  • Drink water or other beverages either a half hour before or after meals so they don’t make you too full.
  • Prepare foods that are colorful and appealing to the eyes.
  • Try moderate exercise to increase your appetite, as long as your doctor says it’s OK.

Chemo, radiation, targeted therapy, and immunotherapy can cause nausea and sometimes vomiting. But localized radiation for breast cancer is less likely to cause vomiting. It can happen right after treatment or a few days later. Ask your doctor about medications that can make you feel better. Also, keep track of when you’re nauseated. You may be able to spot patterns that can help you get ahead of the problem. Also:

  • Eat small meals more often and avoid greasy foods and citrus.
  • Try foods at room temperature instead of very hot or cold.
  • When you’re nauseated, try bland foods like crackers, gelatin, ice chips, rice, plain mashed potatoes, or applesauce.
  • Avoid smells that bother you while you're eating.

Call your doctor if you have severe nausea or you’re vomiting a lot. If you throw up, wait an hour before you eat or drink anything. Then, begin with ice chips and gradually add foods. Chamomile, ginger root tea, or ginger ale can sometimes help settle your stomach.

Weakness is when you’re not as strong as you were before, or not as strong as you need to be for basic daily tasks. Chemo, hormone therapies, some targeted therapies, and some pain meds could cause weakness.  

Cancer-related fatigue is a distressing and relentless state that has an enormous impact on your ability to function. You don’t have energy to do what you need to do or you feel tired all the time, even when there’s no obvious reason for it. The fatigue is out of proportion to your activity level. The cancer itself or chemo, radiation, hormonal, immunotherapy, and targeted therapies can cause fatigue.

Work with your doctor to adjust your lifestyle to find ways that can keep weakness and fatigue to a minimum. Some good rules of thumb include:

  • Make sure you get enough rest. Sleep at least 7 hours a night, and try to lie down during the day to rest if you’re still tired. Avoid caffeine late in the day.
  • Exercise. Short walks can give you more energy. If you’re more active, you’ll rest better.
  • Save your energy for the things that are really important to you. Get help from family and friends with errands and other chores.
  • If you feel pain, let your doctor know. There are almost always treatments that can help.
  • Eat plenty of iron-rich foods like lean meat, beans, dark, leafy vegetables, and iron-fortified cereals or pasta.
  • If your body has too few red blood cells, a condition called anemia, your doctor may recommend erythropoietin or darbepoetin, treatments that stimulate bone marrow to make red blood cells. You can get them by injection, which you can sometimes do on your own at home. If you get this treatment, your doctor will watch you to see if you have rashes, allergic reactions, and problems with blood pressure.

Chemo, radiation, and some targeted therapies can make your mouth and throat sore. You might even notice sores, or “ulcers,” that can be red and swollen. This is called mucositis. Check with your doctor or dentist to see what can stop your pain. Some options include:

  • Ask your doctor about drugs to ease mouth soreness.
  • Choose soft foods that won’t irritate your mouth, such as scrambled eggs, macaroni and cheese, pureed cooked vegetables, and bananas.
  • Cut food into small pieces.
  • Avoid citrus fruits, spicy or salty items, and rough foods.
  • Avoid very cold or hot beverages

Breast cancer treatments that could cause hair loss include chemo, radiation, hormonal therapy, and targeted therapy.

Not everyone will lose their hair during cancer treatment. It depends on the type of treatment and the dose. Your doctor can tell you if you can expect hair loss. Talk to them. It helps to know what to expect.

Chemotherapy. This is the most common cause of hair loss. 

While some women will notice their hair gets thinner, others will lose it completely, including eyelashes and eyebrows, pubic hair, and arm and leg hair. Sometimes it happens suddenly, or you may have a more gradual loss a few weeks after you start treatment. Sone people use cooling caps to help reduce hair loss due to chemotherapy. Cooling the scalp before, during, and after may reduce the amount of chemo that gets into hair follicles. Since there are some long-term safety concerns about using cooling caps, it's best to talk with your doctor before making the decision to use one.

Some women prepare by getting a short hair style before chemotherapy begins. You can also try hair wraps and wigs.

When hair grows back, the texture may be different, but many women won’t notice any changes. The good news about hair loss from chemotherapy is that it stops once treatment is over. After a few months, hair can regrow completely.

Hormone therapy. You might notice a bit of hair thinning or hair loss, usually in the front or middle part of the head. Hormone therapies work by lowering estrogen levels, but scientists don’t know exactly why they lead to hair loss. It usually takes from 6 months to 2 years to notice hair loss from hormone therapy. It might go away after a year or so, but thinning often lasts for as long as you take the medication. The effects stop a few months after you stop taking the medication.

Targeted breast cancer therapy. These medications, including palbociclib (Ibrance), pertuzumab (Perjeta), and ribociclib (Kisqali) may cause hair loss in some people. You’ll notice it right away and your hair won’t start to grow back until several months after you stop taking these medications. 

Immune therapy. In very rare cases, immunotherapy can also cause hair loss in some people. Some examples are pembrolizumab (Keytruda) and dostarlimab-gxly (Jemperli).

Radiation. Radiation only causes hair loss in the particular part of the body it targets. This may be the nipple or armpit if you have hair there. But it may also be the head if your breast cancer has spread to parts of your head like the brain.

Breast cancer treatments like the chemo drug ixabepilone (Ixempra) and the targeted therapy drug bevacizumab (Avastin) along with a number of hormone therapy treatments or steroids given with chemo can lead you to put on some pounds during breast cancer treatment. 

If you notice you're gaining weight, let your doctor know and see what they think might help you. Don’t go on a diet on your own -- your body needs a lot of nutrients during breast cancer treatment.

Many breast cancer therapies can weaken your immune system and raise your risk of infection. Common areas for infection include:

  • Lungs
  • Mouth
  • Throat
  • Sinuses
  • Skin

Chemotherapy and radiation therapy for breast cancer can decrease the number of white blood cells your body makes. Those cells fight infections. Try to stay out of large crowds and away from sick adults and children for 7 to 10 days after you have chemotherapy. That's when you usually have the fewest white blood cells.

Contact your doctor right away if you get sick. You might notice:

  • Colored mucus in saliva or nasal drainage
  • Fever of 100.5 degrees F or higher
  • Sore or burning throat
  • Swelling, redness, warmth, or pus at injury site
  • Cough or shortness of breath

Your doctor might recommend antibiotics as a precaution. Or they may suggest you get a flu shot before you start chemotherapy.

If your white blood cell counts are too low, your doctor may give you a treatment called G-CSF (granulocyte colony stimulating factor -- Neulasta or Neupogen) or GM-CSF (granulocyte macrophage colony stimulating factor -- Leukine).

Some breast cancer treatments can make you infertile for a while. In some cases, treatments could make you infertile forever. The effect depends in part on how long you’re on treatment, the dosage, your age, and other factors.

Here are some ways that cancer therapies can affect your fertility:

  • Chemotherapy may lower the number of eggs your body releases to be fertilized.
  • Radiation may damage your ovaries and uterus.
  • Hormone therapy may interrupt your menstrual cycles and make it harder to conceive.

If you think you might want to get pregnant after your cancer treatments are done, talk with your doctor about fertility preservation methods, such as collecting eggs to freeze for later use.

Some people call this “chemo brain.” But you can have this common kind of mental fog even without chemotherapy, or from other cancer treatments such as radiation, immunotherapy, and hormone therapy. You may notice problems during and after your treatments. There is no proof that these cognitive issues lead to dementia. Symptoms may include:

  • Forgetfulness
  • Trouble concentrating
  • Mild memory loss, such as names and dates
  • Difficulty multitasking

These problems usually go away within 6-12 months after your treatment ends. But some people may have cognitive issues for years.

Cancer treatments can affect you mentally as well as physically. For example, some treatments can set off inflammatory immune reactions that may lead to depression, anxiety, and other mood changes. You may feel:

  • Irritable
  • Worried
  • Unmotivated
  • Uninterested in sex or other activities
  • Hopeless
  • Anxious

Cancer can be a life-changing diagnosis. Many people have times when they feel overwhelmed emotionally or mentally by it. Talk to your doctor so you can figure out if the symptoms stem from your treatments. Different types of psychotherapy and mental health counseling may help you get through this time.

Different people can have different responses to the same breast cancer treatments. That’s why it’s important to tell your health care team about all of your reactions. Some side effects you might want to look out for that are not listed above include:

Chemotherapy: May cause digestive issues (diarrhea, constipation), tingling, numbness, pain, skipped periods, or early menopause. Your doctor may be able to remedy many of these side effects with supportive medications.

Radiation: May cause pain, burning, swelling, and skin discoloration (typically red) at the site of radiation (often the breast). There may even be blistering or peeling of the skin.  In rare cases, the radiation may burn a bit of the lung and cause it to swell (pneumonitis). The risk changes depending on the size of the area that gets radiation. And the swelling in the lung tissue tends to go away with time.  

Hormone therapy: The drug tamoxifen, which blocks estrogen from attaching to cancer cells, can lead to hot flashes and vaginal dryness, discharge, or bleeding. It may also be linked in very rare cases to cataracts, blood clots, and uterine cancer.

A similar group of drugs called aromatase inhibitors, or AIs, may cause hot flashes, vaginal dryness, and muscle and joint pain. They also could raise your risk of osteoporosis and broken bones. In rare cases, scientists have linked them to thinning hair and higher cholesterol. Some AI meds seem to have fewer side effects for different women, though it’s not yet clear why. So ask your doctor if switching might help with your side effects. 

Immunotherapy: Immunotherapy drugs may cause flu-like symptoms -- fever, chills, body aches, sore throat, runny nose -- and GI issues like diarrhea.

Call your nurse or doctor if you have:

  • A temperature over 100.4 F. If you have any fever or chills, tell your doctor right away. If you can’t get in touch with your doctor, go to the emergency room.
  • New mouth sores, patches, a swollen tongue, or bleeding gums
  • A dry, burning, scratchy, or "swollen" throat
  • A cough that is new or doesn’t go away
  • Changes in how your bladder works, including a need to go urgently or more often, burning when you pee, or blood in your urine
  • Digestive changes, including heartburn; nausea, vomiting, constipation, or diarrhea that is severe or lasts longer than 2 or 3 days; or blood in your stools