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

If your oncologist has talked to you about starting an antibody-drug conjugate (ADC) to treat HR-positive/HER2-negative (hormone receptor/human epidermal growth factor receptor 2) metastatic breast cancer, you’ve likely already tried other treatments — hormone therapy, targeted therapy, traditional chemotherapy — that haven’t worked. But there’s reason for hope: Antibody-drug conjugates 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.

Antibody-drug conjugates are a type of targeted therapy. They use monoclonal antibodies to deliver chemotherapy directly to cancer cells, making treatment more precise and more likely to spare healthy cells from damage, says Ranju Gupta, MD, a hematologist and medical oncologist at Lehigh Valley Hospital Hematology Oncology—Muhlenberg in Bethlehem, Pennsylvania.

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

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 stay after the infusion to be monitored for potential rare treatment reactions, 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.

Antibody-drug conjugate infusions are divided into cycles. Your exact treatment schedule will depend on which drug you’re getting:

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

Here’s what you can expect during treatment.

What you experience during treatment will depend on a number of factors, including how many rounds of treatment you undergo and which antibody-drug conjugate you are receiving.

Click on the common side effects below to learn how to manage them.

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

• Chest Pain, Cough, 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. If you’re taking sacituzumab govitecan, your doctor will monitor for rare heart-related issues with an echocardiogram (ultrasound of the heart).
• Eye Problems If you take datopotamab deruxtecan, talk to your doctor if you have new eye symptoms or if 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 have any redness, pain, sores, swelling, or ulcers.
• Other Side Effects Your doctor may also monitor you for anemia (low red blood cell or hemoglobin levels), lung and kidney problems, 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 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 you can use to 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.

Living with HR-positive/HER2-negative metastatic breast cancer can be challenging, but advances such as antibody-drug conjugates offer more treatment options and new reasons for hope. Staying informed and engaged in your care can help you and your care team make decisions that support your health, priorities, and quality of life.

As you continue treatment, remember that your voice remains an important part of every decision. Keep communicating with your oncology care team about symptoms, side effects, and goals, so they can help you get the most benefit from treatment while supporting your overall well-being.