Pertuzumab (Perjeta; Poherdy; pertuzumab in Phesgo)

Medicine at a glance

Pertuzumab is a targeted antibody treatment that attaches to HER2, a protein on some cancer cells. Perjeta contains pertuzumab for infusion into a vein. Poherdy, whose full biological name is pertuzumab-dpzb, is a verified pertuzumab biosimilar: a medicine shown to be highly similar to its reference biological medicine without clinically meaningful differences in safety or effectiveness. Your team records the exact product you receive.

Phesgo is a different formulation containing both pertuzumab and trastuzumab, together with an enzyme that helps the medicine spread beneath the skin. It is injected into the thigh. Its doses and appointment instructions differ from those for an intravenous pertuzumab infusion. These products are administered by healthcare professionals, usually once every three weeks.

The main practical priorities are keeping heart-monitoring appointments, reporting diarrhoea early, recognising treatment reactions and following the precautions for your accompanying medicines. Targeted treatment can still cause serious side effects. The information below supports the individual plan from your cancer team.

What pertuzumab is and how it works

HER2 sits on the outside of cells and helps transmit growth signals. Some tumours have unusually large amounts of this protein. Pertuzumab attaches to HER2 and interferes with its ability to pair with related proteins, reducing signals that encourage cancer cells to grow. It can also help immune cells recognise and attack the antibody-coated cells. This immune action does not make it an immune-checkpoint inhibitor.

Pertuzumab is often prescribed with trastuzumab, which attaches to a different part of HER2. The medicines complement one another. Chemotherapy may be given during part of the course, and its side effects contribute to the overall experience.

Some specialist plans use pertuzumab with trastuzumab deruxtecan, also called Enhertu. This is an antibody–drug conjugate carrying a cell-killing medicine, not ordinary trastuzumab or Phesgo. It has additional precautions, particularly for lung inflammation. Know the full names on your treatment plan rather than relying on the shared word “trastuzumab”.

How the team decides whether it is suitable

The team considers your diagnosis, HER2 test result, previous treatment, general health and the prescribing information relevant to your proposed plan. A laboratory examines tumour tissue for excess HER2 protein, using immunohistochemistry, or extra copies of the HER2 gene, using in situ hybridisation. These are often shortened to IHC and ISH. An uncertain result may need clarification before treatment.

HER2-positive is not interchangeable with the terms HER2-low or HER2-ultralow used for certain other medicines. Having a treatment option directed at HER2 does not automatically mean pertuzumab is suitable. The oncologist interprets the actual report alongside your clinical situation.

Heart health is especially important. Previous heart failure, poorly controlled blood pressure, some abnormal heart rhythms, certain chemotherapy drugs and radiotherapy to the chest can affect the decision. Severe kidney problems and liver impairment also require individual assessment because evidence is limited in these groups.

Ask what treatment is intended to achieve, how benefit will be assessed and when the plan will be reviewed. The presence or absence of side effects does not show whether the medicine is working.

Before treatment starts

Tell your team about heart or lung disease, breathlessness, ankle swelling, recent infections, persistent diarrhoea and any previous reaction to pertuzumab, trastuzumab or another biological medicine. For Phesgo, reactions to its hyaluronidase component also matter. Bring a list of prescription medicines, pharmacy remedies, vitamins and herbal products.

You will have a heart assessment, usually including an echocardiogram, which is an ultrasound scan, or a MUGA scan. These measure left ventricular ejection fraction, or LVEF: the proportion of blood pumped out of the heart’s main pumping chamber with each beat. A normal pulse or blood-pressure reading cannot replace this assessment.

The acceptable starting LVEF depends on the treatment setting. For example, the Perjeta–trastuzumab prescribing information uses at least 50% in one setting and at least 55% in another, with a separate requirement after anthracycline chemotherapy. These are specialist treatment criteria, not numbers for you to interpret alone.

Blood tests usually check blood counts, liver function, kidney function and relevant salts. Infection screening depends on the complete treatment plan and your history. A pregnancy test is needed if you could become pregnant. Discuss fertility preservation before treatment begins if future parenthood matters to you.

Before leaving the first appointment, have the hospital’s urgent advice details, the temperature threshold it uses, instructions for diarrhoea and nausea, and the dates of your next treatment and heart scan.

How treatment is given

Intravenous pertuzumab

The usual first dose is 840 mg over 60 minutes. Subsequent doses are normally 420 mg every three weeks, infused over 30–60 minutes if tolerated. These fixed doses are not calculated from body weight. The infusion goes through a cannula, port or other suitable intravenous line.

Observation adds to appointment time. The US Perjeta warning recommends watching closely for 60 minutes after the first infusion and 30 minutes after later ones; European information recommends 60 minutes initially and 30–60 minutes subsequently. The team may observe you longer after a reaction. Other drugs and their observation periods can make the whole visit considerably longer.

When pertuzumab is paired with ordinary trastuzumab, they are given separately and may be given in either order; a taxane chemotherapy infusion follows them. In plans containing an anthracycline, the antibodies are normally started after that part of chemotherapy is completed. With Enhertu, the current US partner instructions place pertuzumab 30 minutes after Enhertu. Your team follows the actual regimen rather than combining these sequences.

Phesgo under the skin

Phesgo is given by a trained healthcare professional into the thigh, alternating sides and avoiding sore, bruised or damaged skin. Its initial dose contains 1,200 mg pertuzumab and 600 mg trastuzumab, given over about eight minutes. Maintenance contains 600 mg of each antibody, given over about five minutes every three weeks. Observation lasts at least 30 minutes after the initial dose and 15 minutes after maintenance doses.

The different pertuzumab amounts reflect the formulation and route. Do not compare milligram numbers to decide that one is stronger. A clinician can arrange a change from separate infusions to Phesgo using its specific transition rules; it is not a simple vial-for-vial substitution or a home self-injection.

Premedication, delays and practical details

Premedicines depend on your accompanying treatment and reaction history. Steroids used with chemotherapy are not necessarily a requirement for every pertuzumab infusion. After a mild Phesgo reaction, the team may consider medicines before subsequent doses. Emergency treatment for a serious reaction is available wherever these products are administered.

Contact the clinic promptly if you miss an appointment. With less than six weeks between pertuzumab infusions, the maintenance dose is usually given as soon as possible. At six weeks or more, the loading dose is repeated. Phesgo also has a six-week threshold, but uses its own initial and maintenance doses. The team separately checks companion-medicine instructions and whether a safety-related delay has resolved.

Vomiting after treatment does not remove an infused or injected dose, so you do not need a replacement dose. Report repeated vomiting because dehydration still needs treatment. There is no pertuzumab-specific fasting requirement. Pharmacy staff manage preparation, refrigerated storage and disposal; do not attempt to prepare or administer a vial yourself.

Monitoring and checking whether treatment is working

At appointments, describe bowel changes, breathing, swelling, energy levels, skin problems and any symptoms after the last infusion. Bring a brief symptom record if remembering everything is difficult. Blood tests depend partly on the other medicines being given. Low blood counts during chemotherapy may change that treatment even when the antibody plan is considered separately.

Heart scans are repeated during treatment, commonly about every 12 weeks, with timing adjusted to the setting and your risk. A fall in LVEF may be detected before symptoms appear. Treatment may be held for several weeks while heart function is reassessed, and significant or persistent problems can mean stopping it.

The team uses examination, imaging and other appropriate assessments to evaluate benefit. Treatment length varies: some plans have a defined course, while others continue while benefit and tolerability justify treatment. Finishing chemotherapy does not necessarily mean the pertuzumab-containing part has finished.

Pertuzumab dose reductions are not recommended in its standard prescribing information. Slowing an infusion, delaying a dose or stopping treatment are different decisions. A companion drug can have its own dose-reduction rules. Pertuzumab is not given alone: if its partner is stopped, the team must reassess the whole plan.

Common side effects and practical management

Diarrhoea

Diarrhoea is particularly important with pertuzumab and can continue after chemotherapy ends. It may be more troublesome when a taxane is also being given, and older patients need particular attention to fluid loss. Report it early rather than waiting until you are exhausted or dehydrated.

Record how often you go compared with your usual pattern. Follow the anti-diarrhoea plan provided, which may include loperamide, and take frequent small drinks. Oral rehydration solution can help replace salts, but follow any heart- or kidney-related fluid restriction. Small, manageable meals may be easier than large ones.

Contact the team urgently if diarrhoea is increasing, persists despite treatment, wakes you repeatedly, or comes with fever, blood, severe pain, dizziness or reduced urine. Do not simply keep increasing anti-diarrhoea medicine without advice. Severe diarrhoea can require intravenous fluids and a treatment pause.

Nausea, reduced appetite and mouth soreness

Take prescribed anti-sickness medicines as directed. Try small meals, regular sips and foods you find tolerable. Let the team know if weight is falling or eating is becoming difficult. Mouth ulcers and soreness may be affected by accompanying chemotherapy; gentle cleaning with a soft toothbrush and the recommended mouth-care routine can help. Painful swallowing or inability to drink needs prompt advice.

Tiredness and changes in blood counts

Balance rest with manageable activity. New or markedly worse fatigue should be assessed rather than automatically attributed to treatment. Anaemia means fewer red blood cells and can cause tiredness or breathlessness. Low white cells increase infection risk, while low platelets can cause bruising or bleeding. These effects depend heavily on the combination being used.

Skin, nails, hair and nerves

Dryness, rash or itching can occur. Use a gentle cleanser and moisturiser, protect skin from strong sunlight, and report a spreading or painful rash. Nail tenderness, hair loss and tingling or numbness are also seen in treatment combinations; chemotherapy may be a major contributor. Report nerve symptoms early if they affect buttons, walking or balance. Their appearance does not prove pertuzumab is the sole cause.

Less common but important side effects

Reduced heart pumping function

Pertuzumab-containing treatment can weaken heart pumping, sometimes without initial symptoms. Contact the oncology team promptly for new breathlessness, needing extra pillows to sleep, swollen ankles, an unusually fast heartbeat or rapid unexplained weight gain. These symptoms can also have other causes and need assessment. Severe breathlessness, chest pain or collapse is an emergency.

Infusion, injection and allergic reactions

A reaction can cause chills, fever, flushing, itching, rash, headache, dizziness, nausea or pain. Tell the nurse immediately, even if symptoms seem mild. The infusion or injection may be slowed or stopped and treatment given. Severe allergy can cause throat swelling, wheezing, marked breathing difficulty or collapse and may require permanent discontinuation. Reactions can be life-threatening.

Phesgo can also cause local soreness, redness or swelling. Report worsening pain or spreading redness rather than assuming every injection-site change is harmless. Pain, burning, swelling or leakage around an intravenous line should be reported immediately.

Serious infection

Fever with low neutrophils, a type of white blood cell, is called febrile neutropenia. The risk is especially relevant during combinations containing chemotherapy. Diarrhoea and mouth inflammation may add to infection concerns. Seek urgent advice for fever, shaking chills or feeling suddenly very unwell, even if the temperature is normal.

Lung problems and partner-specific risks

New cough or breathlessness needs prompt assessment. Infection, heart failure and lung inflammation can feel similar. The trastuzumab-containing Phesgo formulation carries specific warnings about serious lung toxicity. If your partner medicine is Enhertu, its lung-inflammation warning is particularly important: report new or worsening breathing symptoms immediately, including a dry cough or fever. Do not wait for a scheduled scan. The team may hold treatment and arrange investigations. Confirmed lung inflammation causing symptoms requires permanent discontinuation of Enhertu. Do not assume a delayed dose can go ahead before the specialist completes the assessment.

Other medicines, supplements and vaccinations

Give the pharmacist an up-to-date list of everything you use, including over-the-counter pain medicines, supplements and traditional or herbal preparations. The review must cover the whole regimen, not just pertuzumab. There is no standard grapefruit or acid-suppressant spacing rule in the pertuzumab infusion instructions, but another medicine can have different requirements.

Medicines that can affect the heart need particular attention. Anthracycline chemotherapy may increase cardiac risk around trastuzumab-containing treatment; US Phesgo information advises avoiding anthracyclines, if possible, for up to seven months after stopping it. If needed sooner, the specialist plans close cardiac monitoring. Do not start or stop heart medicines independently.

Discuss vaccinations with your team. Non-live vaccines may be useful, but timing and response depend on the treatment course. Live vaccines may be unsuitable while the immune system is weakened by accompanying treatment. Do not assume that an antibody infusion makes every vaccine prohibited or every vaccine safe.

Everyday life during treatment

Plan the first appointment with extra time and, if possible, help getting home. Later visits may be shorter, but observation, blood tests and other medicines still take time. Work and travel arrangements are easier when they allow flexibility for tiredness, diarrhoea and unexpected delays.

Do not drive or use machinery if dizzy, faint, unwell after treatment, or affected by sedating premedicines. Gentle activity may help maintain strength, but stop and seek advice for unexpected breathlessness, chest discomfort or light-headedness.

Use normal food hygiene, wash hands regularly and avoid close contact with people who are clearly infectious, particularly when blood counts are low. Tell your dentist and other healthcare professionals about all cancer medicines before procedures. The team can advise on safe timing when chemotherapy affects blood counts.

You can discuss sex, vaginal dryness, body-image changes, anxiety and fatigue with your team. These concerns deserve attention alongside blood tests and scans. Intimacy is possible when comfortable, with contraception and any treatment-specific precautions agreed in advance.

Fertility, contraception, pregnancy and breastfeeding

Pertuzumab-containing treatment can harm an unborn baby. Arrange pregnancy testing before treatment if relevant, and tell the team immediately about a possible pregnancy during treatment or the precaution period afterwards. Specialist assessment is needed; do not wait until the next cycle.

Use effective contraception throughout treatment. US Perjeta information specifies seven months after the last dose when given with trastuzumab. The European Perjeta-only wording says six months, but accompanying trastuzumab requires seven months; the shorter interval must not shorten the combination plan. Phesgo specifies seven months after its last dose. If drugs finish on different dates, ask the team to write the final contraception end date.

Contraception advice for a male patient depends on the accompanying medicines as well. For example, the current US Enhertu information specifies contraception during treatment and for four months afterwards for males with partners who could become pregnant; its female interval is seven months. Do not infer that an absent male interval in the pertuzumab label removes a partner drug’s precautions.

Breastfeeding needs an explicit plan before treatment. European Phesgo and Herceptin information advises no breastfeeding during treatment and for at least seven months afterwards. US Perjeta and Phesgo information instead requires an individual benefit–risk assessment that accounts for trastuzumab’s seven-month washout. Enhertu specifies no breastfeeding during treatment and for seven months afterwards. Follow the complete regimen’s restriction and do not restart without specialist advice.

The effect of pertuzumab alone on human fertility is not well established. Chemotherapy and other partner medicines can affect fertility, so discuss preservation options before starting. Missing periods does not establish infertility or remove the need for contraception.

After treatment finishes

Ask for a written follow-up plan covering heart checks, persistent side effects, scans and reproductive precautions. Heart problems may need assessment after treatment has ended. As one formulation-specific example, US Phesgo information recommends LVEF checks every six months for at least two years after completion when it was used as adjuvant treatment. Your schedule depends on the full course and any cardiac findings.

Continue to report new breathlessness, swelling or unexplained exhaustion. Keep a record of the medicines and final treatment dates for future clinicians, especially before further treatment that may affect the heart. Persistent diarrhoea, nerve symptoms or fatigue can need practical support even when infusions have stopped.

Frequently asked questions