The FDA approved Phesgo four months ahead of schedule in response to the coronavirus (COVID-19) pandemic, allowing patients to limit their exposure to healthcare facilities.
Created by Genentech, Phesgo combines Herceptin (trastuzumab), Perjeta (pertuzumab), and hyaluronidase-zzxf into a single injection.
Typically, Herceptin and Perjeta are given intravenously (IV, directly into a vein) in a clinic, infusion center, or hospital. Because Phesgo is given as an injection, it’s possible to receive at home from a healthcare professional. It’s also much faster, only taking about five to eight minutes to administer.
How Does It Work?
Phesgo’s main components, Herceptin and Perjeta, are not considered chemotherapy, but rather “targeted or biological therapy often combined with chemotherapy, especially at the beginning of treatment," David Riseberg, MD, chief of medical oncology and hematology at Mercy Medical Center in Baltimore, Maryland, tells Verywell Health.
When injected under the skin, Phesgo releases the protein hyaluronidase to increase the body’s absorption of Herceptin and Perjeta. Once absorbed, Herceptin and Perjeta bind to cells that have the HER2 protein and stop signals that contribute to the growth of cancer.
It may seem strange that Phesgo, which is administered in a few minutes, can be just as effective as IV Herceptin and Perjeta, which takes an hour or longer.
However, the results of a Phase III study—presented at the 2019 San Antonio Breast Cancer Symposium—revealed that there was no significant difference between the effectiveness of Phesgo versus IV Herceptin and Perjeta.
How Is Phesgo Administered?
Only a healthcare professional, such as a registered nurse, can give a patient Phesgo. The healthcare professional can administer Phesgo in your home or in a medical facility. Here are three things you can expect when receiving Phesgo:
For your initial dose, your healthcare professional will slowly inject Phesgo into your thigh over the course of eight minutes. They will monitor you for 30 minutes afterward for any reactions. Every three weeks, a maintenance dose of Phesgo will be injected over the course of five minutes. Your healthcare professional will monitor you for 15 minutes thereafter for reactions. You should alternate between the left and right thigh during each visit to avoid injection site complications, such as scarring or hardened skin.
Side Effects
The Phase III study found that Phesgo had similar side effects as IV Herceptin and Perjeta. The most common side effects include:
Alopecia (hair loss) NauseaDiarrheaAnemia (reduced number of red blood cells)Lack of energy
Dr. Riseberg says a side effect that may occur with Phesgo but not IV Herceptin and Perjeta an injection site reaction, like redness or itching. Most of the time, Benadryl can treat any such reactions.
If chemotherapy is part of your treatment schedule, Phesgo can raise your risk of getting neutropenia (low white blood cells) which increases your risk of infection. For this reason, your doctor will most likely monitor your white blood cell count as you take Phesgo.
Serious side effects of Phesgo include heart and lung problems. The FDA also warns that exposure to Phesgo during pregnancy or seven months before conception can result in fetal harm.
Serious—and rare—injection reactions can include anaphylaxis, a severe, potentially life-threatening allergic reaction which can cause difficulty breathing, dizziness, swelling, and an irregular heartbeat.
