What to expect from HER2-targeted therapy for breast cancer

Some breast cancer cells have increased HER2 protein or gene activity, which can encourage growth. HER2-targeted medicines interfere with that signalling or help the immune system recognise the affected cells. Testing of the tumour confirms whether HER2-directed treatment is relevant. The plan may be used before or after surgery, with chemotherapy, with hormone treatment, or for cancer that has spread, depending on the clinical situation. Your team explains the specific medicine, route, and treatment sequence.

Before and during treatment, tell your team about heart disease, breathlessness, pregnancy, allergies, and all medicines or supplements. Appointments may include an infusion or injection, symptom review, and tests of heart function when indicated. Report diarrhoea, rash, fever, chills, unusual tiredness, swelling, or new breathlessness rather than waiting for the next visit. Keep a treatment diary and ask which medicines can relieve side effects. Explore [HER2-Targeted Therapy](/treatments/systemic-therapy/her2-targeted-therapy/) and [Breast Cancer](/conditions/breast-cancer/).

Contact your oncology team promptly for fever, signs of infection, persistent vomiting or diarrhoea, or a new rash. Seek emergency help for sudden or worsening breathlessness, chest pain, fainting, severe swelling, or symptoms of a severe allergic reaction during or after treatment. Early reporting helps the team assess whether treatment, fluids, or other support is needed.

Which test confirmed HER2 status, and what does it mean for my plan? Will treatment be an infusion, injection, or both? How will my heart and other organs be monitored? Which symptoms require a same-day call? How will this treatment fit with surgery, chemotherapy, or hormone treatment?