Phesgo 600mg/600mg Injection contains pertuzumab and trastuzumab, two humanised monoclonal antibodies that target the human epidermal growth factor receptor 2 (HER2). The 10ml vial contains 600mg of pertuzumab and 600mg of trastuzumab, along with hyaluronidase to facilitate absorption following subcutaneous administration.

Phesgo is used with chemotherapy to treat adults with HER2-positive early breast cancer at high risk of recurrence and HER2-positive metastatic or locally recurrent unresectable breast cancer. The tumour must be confirmed as HER2-positive using an appropriately validated testing method.

Phesgo is used in combination with chemotherapy for:

• HER2-positive early breast cancer at high risk of recurrence, including locally advanced or inflammatory breast cancer in the neoadjuvant setting

• HER2-positive early breast cancer at high risk of recurrence in the adjuvant setting

• HER2-positive metastatic breast cancer or locally recurrent unresectable breast cancer in adults who have not received previous anti-HER2 therapy or chemotherapy for metastatic disease

In metastatic breast cancer, Phesgo is used in combination with docetaxel. The treatment plan depends on the stage of cancer, previous treatment and the patient's clinical condition.

Pertuzumab and trastuzumab both target HER2 but bind to different regions of the receptor.

Pertuzumab binds to a region of HER2 involved in receptor pairing with other HER family receptors, while trastuzumab binds to a different region of HER2. Together, they inhibit HER2 signalling more comprehensively and can reduce the growth and survival of HER2-positive cancer cells.

Phesgo also contains hyaluronidase, which temporarily modifies the tissue under the skin and allows the fixed-dose combination of pertuzumab and trastuzumab to be administered subcutaneously.

Tell your doctor about all medicines and cancer treatments you are receiving, including prescription medicines, over-the-counter medicines, vitamins and herbal supplements.

Particular attention is required when Phesgo is given with chemotherapy, especially anthracyclines, because both HER2-targeted treatment and certain chemotherapy medicines can affect heart function. Your oncologist will determine the appropriate treatment sequence and monitoring.

Phesgo should not be combined with other medicines containing pertuzumab or trastuzumab unless specifically prescribed as part of a planned treatment switch.

• Store Phesgo at 2°C to 8°C in a refrigerator.

• Do not freeze.

• Keep the vial in the original carton to protect it from light.

• Do not shake the vial.

• Phesgo is supplied as a single-use vial.

• The medicine should be prepared and administered using appropriate aseptic technique by a healthcare professional.

Phesgo 600mg/600mg Injection is administered subcutaneously, not intravenously.

The 600mg/600mg formulation is the maintenance dose and is administered once every 3 weeks following the initial loading dose of Phesgo 1200mg/600mg.

The maintenance dose is injected under the skin of the thigh over approximately 5 minutes. The injection site should be alternated between the left and right thigh, with each new injection given at least 2.5cm away from the previous injection site and only into healthy skin.

Patients should be observed for injection-related and hypersensitivity reactions for approximately 15 minutes after the maintenance dose. The initial loading dose requires a longer observation period.

If a scheduled dose is delayed by 6 weeks or more, a loading dose of 1200mg pertuzumab/600mg trastuzumab should generally be administered before returning to the 600mg/600mg maintenance schedule.

Phesgo can cause side effects, although not everyone experiences them. Some adverse effects are related to pertuzumab or trastuzumab, while others may occur because of the chemotherapy given alongside Phesgo.

Common side effects

• Diarrhoea

• Nausea

• Vomiting

• Fatigue

• Hair loss

• Rash

• Decreased appetite

• Muscle or joint pain

• Headache

• Injection-site reactions

• Anaemia or other changes in blood cell counts

The frequency and severity of side effects depend partly on whether Phesgo is being used with chemotherapy and the treatment setting.

Serious side effects

Seek immediate medical attention for:

• Severe allergic or hypersensitivity reactions

• Severe injection-related reactions

• Shortness of breath or other symptoms of serious lung complications

• Signs of heart failure, such as new or worsening breathlessness, persistent cough, swelling of the legs or unusual fatigue

• Significant reduction in heart function

• Severe diarrhoea or dehydration

• Severe infection or other serious complications associated with chemotherapy

Heart dysfunction is an important safety concern with HER2-targeted treatment. Your doctor may assess left ventricular ejection fraction before and during treatment.

• Phesgo should be started under the supervision of a doctor experienced in administering anticancer medicines.

• The first dose is a loading dose of 1200mg pertuzumab/600mg trastuzumab. The 600mg/600mg formulation is used for subsequent maintenance doses.

• Do not confuse the 600mg/600mg maintenance formulation with the 1200mg/600mg loading formulation.

• Your heart function may be assessed before and during treatment because pertuzumab and trastuzumab can affect cardiac function.

• Report new breathlessness, persistent cough, swelling of the legs, unusual fatigue or rapid weight gain promptly.

• Report severe diarrhoea, fever, rash, breathing difficulty or other significant symptoms to your healthcare team.

• Attend all scheduled appointments and laboratory or cardiac assessments.

• If a dose is missed or significantly delayed, do not try to compensate with an extra dose. Your oncologist will determine whether a loading dose is required.

• Effective contraception is important during treatment and for 7 months after the last dose.