How long does HER2-targeted therapy take to work for breast cancer?

The treatment works by attaching to or blocking HER2 signals on cancer cells. A change in symptoms or the feel of a breast area can happen before a scan gives a clear answer, and some people notice no immediate change even when treatment is helping. The schedule depends on whether therapy is given before surgery, after surgery, or for breast cancer that has spread. Other medicines, including chemotherapy or hormone treatment, may be used alongside it. Your team may compare examination findings, imaging, and laboratory results at planned reviews rather than judging the treatment after one dose.

Attend each infusion and review appointment, and keep a record of new symptoms, breast or chest changes, appetite, and energy. Tell the oncology team about medicines, supplements, pregnancy plans, or heart and breathing conditions before treatment starts. Do not stop a targeted medicine because the first visits feel unchanged; the team may need several assessments before deciding whether to continue, adjust, or combine treatment. Ask when your first formal response assessment is planned and which changes should be reported between visits.

Contact your treatment team promptly for fever, chills, a new cough, worsening breathlessness, chest pain, fainting, marked swelling, or a sudden change in how you feel after an infusion. Seek emergency help for severe breathing difficulty, collapse, or signs of a serious allergic reaction such as swelling of the face or throat. These symptoms need attention because HER2-targeted medicines can affect infusion reactions, the lungs, or the heart; they do not show whether the cancer treatment is working.

Which HER2-targeted medicine am I receiving, and when will you first assess its effect? What findings will you use to judge response? Is my treatment planned before surgery, after surgery, or for disease outside the breast? Which symptoms should prompt a same-day call?