What to Expect From an Antibody-Drug Conjugate for HR+/HER2- Metastatic Breast Cancer

If your oncologist has talked to you about antibody-drug conjugates (ADC) to treat HR-positive/HER2-negative metastatic breast cancer, you’ve likely already tried other treatments, such as chemotherapy, immunotherapy, and hormone therapy, that haven’t worked. But there’s reason to have hope: ADCs appear to be more effective than traditional chemotherapy for slowing cancer progression and extending survival.

“Antibody-drug conjugates have emerged as an almost revolutionary therapeutic class,” says Jasmeet Singh, MD, a breast oncologist at Memorial Sloan Kettering Cancer Center in West Harrison, New York.

ADCs are a type of targeted therapy. They use chemotherapy against cancer cells in a very targeted way that is highly effective and spares healthy cells from damage, explains Ranju Gupta, MD, hematologist and medical oncologist at Lehigh Valley Hematology Oncology-Muhlenberg in Bethlehem, Pennsylvania.

In doing so, these drugs have the potential to shrink tumors or slow their growth while minimizing the side effects, which may allow them to be used for ongoing treatment.

ADCs are administered like standard chemotherapy — intravenously, at an infusion center, which may be at a hospital or doctor’s office.

During your infusion appointment, the ADC treatment will be delivered to your bloodstream through an IV into a vein in your arm.

You can expect to be at the infusion center for a few hours, says Alberto Montero, MD, director of the breast cancer medical oncology program at University Hospitals Seidman Cancer Center in Cleveland. The first time will be the longest, because you’ll need to stay after the infusion to be monitored for any rare potential reactions to the treatment, such as shortness of breath. If you don’t have any adverse reactions, later appointments may take closer to an hour and not require monitoring afterward.

Get Blood Work Done Beforehand

You’ll probably have a complete blood count to check your health status before each round of ADCs. “We usually ask you to get blood work before you come in for your treatment,” says Jack Jacoub, MD, an oncologist and the medical director of MemorialCare Cancer Institute at Orange Coast and Saddleback medical centers in Orange County, California. “We check your blood counts and your kidney and liver function.”

Eat a Light Meal Before You Go

A few hours before you go in, eat a small, high-fiber meal, such as nuts or cottage cheese with fruit. This will help lessen the side effects you may experience later, such as constipation. Drink lots of water before you go in, too, Dr. Jacoub says.

Pack a Bag

Wear comfortable clothes that are easy to sit in. You may get cold, so bring a bag with warm socks and a blanket. You can also bring water and healthy snacks, such as fruit and crackers.

Bring Entertainment

You can’t move with the IV needle in your arm, so you’ll need to stay still for a while. Bring a good book, crossword puzzles, some magazines, a tablet, or your favorite music to help the time pass. (Remember to bring headphones or earbuds.)

Ask a Friend or Family Member to Join You

It’s good to have a friend or loved one drive you to and from appointments. They can also focus on writing down instructions or any answers to questions you have. They may even be allowed to keep you company during the infusion. You can ask the center.

What you experience during ADC treatment will depend on a number of factors, including how many rounds of treatment you undergo and which ADC you are receiving. It can be different for every person.

Common Side Effects

These common side effects tend to be relatively mild:

There’s also a chance you could have more serious side effects:

• Cough, chest pain, or shortness of breath: If you take trastuzumab deruxtecan, talk to your doctor if you experience any of these side effects, which can be signs of a lung problem called pneumonitis.
• Heart issues: While taking trastuzumab deruxtecan, your doctor will monitor you for the rare risk of congestive heart failure. Your doctor will also monitor for rare heart-related issues, using an echocardiogram (ultrasound of the heart), if you’re taking sacituzumab govitecan.
• Eye problems: If you take datopotamab deruxtecan, talk to your doctor if you have new eye symptoms or eye symptoms get worse. Tell them if you have changes in tear production, changes to your vision, discharge, dryness, eye crusting, irritation, light sensitivity, pain, redness, or swelling.
• Mouth sores: While undergoing treatment with datopotamab deruxtecan, it’s possible to develop mouth ulcers and sores that can become severe. So be sure to tell your doctor if you experience any redness, pain, sores, swelling, or ulcers.
• Other side effects: Your doctor may also monitor you for lung and kidney problems, anemia (low iron levels), and neutropenia (a decrease in white blood cell count), which can cause a life-threatening infection in severe cases.

If at any point during treatment you feel like you’re having unusual side effects — or aren’t sure if you should worry about what you’re experiencing — don’t hesitate to reach out to your care team. “Earlier is better,” says Dr. Montero. “There’s lots of research that the sooner your oncology team is aware of something, the less potential for an extreme toxicity.”

Many cancer centers have a phone line where you can reach an on-call nurse or doctor, even after hours. Before your first infusion, be sure to ask your care team who to contact if any red flags come up.

ADC infusions are divided into 3-week cycles. Your exact treatment schedule will depend on which drug you take:

• Both datopotamab deruxtecan and trastuzumab deruxtecan are given once every 3 weeks.
• Sacituzumab govitecan consists of 21-day cycles, where the treatment is given on day 1 and day 8, followed by a break through day 21.

Here’s what you can expect during treatment.

The number of treatment cycles you’ll need — with any type of ADC — is determined by your particular case. “It’s typically open ended,” says Montero, and depends on how well you’re tolerating the treatment and whether follow-up scans show that it’s helping.