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PubMed This is a summary of 19 peer-reviewed journal articles Updated
Medical Oncology · HER2-Positive Breast Carcinoma

Monitoring Your Health and Managing Side Effects

At a Glance

During HER2-targeted treatment, report fever, breathing changes, chest symptoms, swelling, palpitations, or severe diarrhea promptly. Regular heart scans, lung monitoring with Enhertu, and scheduled mammograms and visits help manage risks and detect recurrence.

While HER2-targeted therapies are highly effective, they require careful monitoring to protect your heart and lungs. By staying vigilant and reporting changes early, most side effects can be managed effectively without compromising your long-term health.

Emergency and Urgent Symptoms

It is important to distinguish between expected side effects and those that require immediate medical attention.

Go to the Emergency Room (Call 911) if you experience:

  • Severe Shortness of Breath: Sudden, intense difficulty breathing, even while resting [1].
  • Chest Pain: Pressure, tightness, or sharp pain in the chest that may spread to the arms or neck.
  • Sudden Confusion or Slurred Speech: These could be signs of a rare but serious complication.
  • Fever (100.4°F / 38°C or higher): During chemotherapy, this can be a sign of febrile neutropenia, a life-threatening medical emergency. Do not take fever-reducers or wait until the next day. Call your center’s urgent after-hours number immediately for evaluation [2].

Call your Oncology Team IMMEDIATELY if you notice:

  • New or Worsening Cough: Especially a dry, persistent cough if you are taking T-DXd (Enhertu) [3].
  • Shortness of Breath with Activity: Finding it harder to walk or climb stairs than it was last week [4].
  • Swelling (Edema): New swelling in your ankles, feet, or legs, or sudden weight gain [5].
  • Heart Palpitations: A feeling that your heart is racing, fluttering, or skipping beats.

Protecting Your Heart

Many HER2-targeted drugs, such as trastuzumab and pertuzumab, can temporarily weaken the heart muscle, a condition called cardiotoxicity [6]. This is often measured by your Left Ventricular Ejection Fraction (LVEF), which is the percentage of blood your heart pumps out with each beat.

  • Monitoring Schedule: You will typically have a baseline heart scan (ECHO or MUGA) before starting treatment. For trastuzumab-based regimens, repeat scans are common every 3 months during therapy, though this depends on your baseline risk and specific drug [7] [8].
  • What is a “Drop”?: Doctors look for an LVEF decrease of more than 10 percentage points to a level below 50% [9].
  • Management: If your heart function drops, your doctor may “hold” your HER2 therapy and prescribe heart-protective medications like beta-blockers. In many cases, this heart weakness is reversible, and treatment can be restarted once your heart function recovers [10] [11].

Monitoring Your Lungs (T-DXd)

If you are taking T-DXd (Enhertu), your team will be watching closely for Interstitial Lung Disease (ILD) or pneumonitis (lung inflammation). This is a serious side effect that can be fatal if ignored [12].

  • Grading and Action: Asymptomatic lung changes found on a scan (Grade 1) require interrupting T-DXd treatment and monitoring until resolution. However, if you develop symptoms like a new cough or shortness of breath (Grade 2 or higher), the drug must be stopped permanently, and you will likely be treated with high-dose steroids [13] [14]. Report any new respiratory symptoms instantly.

Managing Digestive Side Effects

Drugs like neratinib or tucatinib are known to cause significant diarrhea [15].

  • Prophylaxis: Routine preventive anti-diarrheal medication like loperamide is highly specific to the drug you are taking (e.g., standard for neratinib). Do not start over-the-counter anti-diarrheals without your team’s exact instructions.
  • Hydration: It is vital to drink plenty of fluids to avoid dehydration if you experience frequent loose stools.

Life After Treatment: Surveillance

Once you complete your year of HER2-targeted therapy for early-stage disease, you move into the “surveillance” phase. The goal is to monitor for recurrence while supporting your recovery.

  • Office Visits: Typically every 3 to 6 months for the first three years, then every 6 to 12 months for years four and five [16].
  • Imaging: You should have an annual mammogram of the conserved or remaining breast [17]. Routine “full-body” scans (like PET or CT scans) or blood tests for “tumor markers” are generally not recommended for asymptomatic early-stage survivors, as they do not improve survival and can lead to unnecessary anxiety and biopsies [18] [19].
  • Long-term Heart Health: Your doctor will individualize a plan for any final heart scans after finishing treatment to ensure your heart has fully recovered [7].

Common questions in this guide

When is a fever during HER2-positive breast cancer treatment an emergency?
A temperature of 100.4°F (38°C) or higher during chemotherapy needs immediate medical evaluation because it may be febrile neutropenia. Call your oncology team's urgent number right away and follow its instructions; do not wait until the next day or take fever-reducing medicine before seeking guidance.
How often will my heart be checked during HER2-targeted treatment?
Most patients have a baseline ECHO or MUGA scan before treatment begins. During trastuzumab-based treatment, heart scans are often repeated about every three months, but the schedule depends on your heart health, risk factors, and specific medicines.
What happens if my LVEF drops during HER2 therapy?
A meaningful drop in LVEF may lead your doctor to pause HER2 treatment and prescribe heart-protective medicine such as a beta-blocker. Heart weakness is often reversible, and treatment may be restarted if heart function improves.
What cough or breathing changes should I report while taking Enhertu?
Report a new or worsening cough, especially a dry cough, or shortness of breath immediately while taking Enhertu. These symptoms can signal interstitial lung disease or pneumonitis, which may require stopping the medicine and treating the lung inflammation with corticosteroids.
Should I take loperamide to prevent diarrhea from HER2 medicines?
The need for preventive loperamide depends on the specific HER2 medicine, and it is commonly part of planned diarrhea prevention with neratinib. Do not start an over-the-counter anti-diarrheal without your oncology team's instructions, and drink fluids to reduce the risk of dehydration.
What follow-up care is recommended after I finish HER2-targeted treatment?
After treatment for early-stage disease, follow-up visits are commonly scheduled every three to six months for the first three years and every six to twelve months during years four and five. An annual mammogram is recommended for the remaining or conserved breast, while routine full-body scans and tumor-marker blood tests are generally not advised when you have no symptoms.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.How often will we be checking my heart function with an ECHO or MUGA scan during my treatment?
  2. 2.What are my baseline LVEF (Left Ventricular Ejection Fraction) and cardiac risk factors?
  3. 3.If I am taking T-DXd (Enhertu), what is our specific plan for monitoring my lungs, and what symptoms should I report immediately?
  4. 4.If we need to pause my HER2 therapy due to a drop in heart function, what is the criteria for restarting it?
  5. 5.Now that I have finished my initial treatment, what is my schedule for follow-up exams and mammograms over the next five years?
  6. 6.Should I be taking any preventive medications, like loperamide, to manage potential diarrhea from my targeted therapy?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (19)
  1. 1

    Trastuzumab Deruxtecan-Associated Interstitial Lung Disease: Real-World Insights from a Tertiary Care Center.

    Alanazi AS, Alanazi AA, Alanizi A, et al.

    Current oncology (Toronto, Ont.) 2025; (32(10)) doi:10.3390/curroncol32100575.

    PMID: 41149495
  2. 2

    Efficacy of a novel interstitial lung disease monitoring program in breast cancer patients undergoing treatment with trastuzumab-deruxtecan.

    Williamson J, Kelley K, Scholand MB, et al.

    Breast cancer research and treatment 2025; (210(2)):487-491 doi:10.1007/s10549-024-07586-2.

    PMID: 39841348
  3. 3

    Multidisciplinary clinical guidance on trastuzumab deruxtecan (T-DXd)-related interstitial lung disease/pneumonitis-Focus on proactive monitoring, diagnosis, and management.

    Swain SM, Nishino M, Lancaster LH, et al.

    Cancer treatment reviews 2022; (106()):102378 doi:10.1016/j.ctrv.2022.102378.

    PMID: 35430509
  4. 4

    Can You Establish the Cause of This Patient's Shortness of Breath?

    Trail A, Rogers J, Ajani J

    Journal of the advanced practitioner in oncology 2023; (14(5)):440-443 doi:10.6004/jadpro.2023.14.5.8.

    PMID: 37576362
  5. 5

    Cardiotoxicity of monoclonal antibody-based therapies in breast cancer: a contemporary narrative review.

    Santos Nussbaum ACA, Antonini M, Mattar A, et al.

    Cardio-oncology (London, England) 2026; (12(1)).

    PMID: 42069784
  6. 6

    Trastuzumab-induced cardiotoxicity: a review of clinical risk factors, pharmacologic prevention, and cardiotoxicity of other HER2-directed therapies.

    Dempsey N, Rosenthal A, Dabas N, et al.

    Breast cancer research and treatment 2021; (188(1)):21-36 doi:10.1007/s10549-021-06280-x.

    PMID: 34115243
  7. 7

    Cardiac function surveillance practices and outcomes in patients with HER2-positive breast cancer treated with trastuzumab: a retrospective cohort study across a safety-net and tertiary care setting.

    Huang L, Manthena P, Su M, et al.

    Cardio-oncology (London, England) 2025; (11(1)):74 doi:10.1186/s40959-025-00376-9.

    PMID: 40842038
  8. 8

    Cardiac safety of dual anti-HER2 blockade with pertuzumab plus trastuzumab in early HER2-positive breast cancer in the APHINITY trial.

    de Azambuja E, Agostinetto E, Procter M, et al.

    ESMO open 2023; (8(1)):100772 doi:10.1016/j.esmoop.2022.100772.

    PMID: 36681013
  9. 9

    Diastolic heart failure is a new clinical entity of trastuzumab-induced cardiotoxicity: a case report.

    Fujita K, Matsumoto K, Kishi A, Kawasaki S

    European heart journal. Case reports 2023; (7(1)):ytac470 doi:10.1093/ehjcr/ytac470.

    PMID: 36582596
  10. 10

    Prospective evaluation of the cardiac safety of HER2-targeted therapies in patients with HER2-positive breast cancer and compromised heart function: the SAFE-HEaRt study.

    Lynce F, Barac A, Geng X, et al.

    Breast cancer research and treatment 2019; (175(3)):595-603 doi:10.1007/s10549-019-05191-2.

    PMID: 30852761
  11. 11

    Heart failure prevention and monitoring strategies in HER2-positive breast cancer: a narrative review.

    Jafari L, Akhter N

    Breast cancer research and treatment 2021; (186(2)):295-303 doi:10.1007/s10549-021-06096-9.

    PMID: 33481134
  12. 12

    Managing the Risk of Lung Toxicity with Trastuzumab Deruxtecan (T-DXd): A Canadian Perspective.

    Henning JW, Brezden-Masley C, Gelmon K, et al.

    Current oncology (Toronto, Ont.) 2023; (30(9)):8019-8038 doi:10.3390/curroncol30090582.

    PMID: 37754497
  13. 13

    Interstitial lung disease in patients treated with antibody-drug conjugates: a review.

    Petrelli F, Dottorini L, D'Alessio A, et al.

    Lung cancer (Amsterdam, Netherlands) 2026; (219()):109532 doi:10.1016/j.lungcan.2026.109532.

    PMID: 42462539
  14. 14

    Successful Trastuzumab-Deruxtecan Rechallenge After Interstitial Lung Disease: A Case Report.

    de Weger VA, Schutte T, Konings IRHM, Menke-van der Houven van Oordt CW

    Journal of breast cancer 2023; (26(5)):519-523 doi:10.4048/jbc.2023.26.e38.

    PMID: 37926069
  15. 15

    Tucatinib vs Placebo, Both in Combination With Trastuzumab and Capecitabine, for Previously Treated ERBB2 (HER2)-Positive Metastatic Breast Cancer in Patients With Brain Metastases: Updated Exploratory Analysis of the HER2CLIMB Randomized Clinical Trial.

    Lin NU, Murthy RK, Abramson V, et al.

    JAMA oncology 2023; (9(2)):197-205 doi:10.1001/jamaoncol.2022.5610.

    PMID: 36454580
  16. 16

    Breast Cancer Follow-Up and Surveillance After Primary Treatment: ASCO Guideline Update.

    Nahleh Z, Alfano CM, Somerfield MR, et al.

    Journal of clinical oncology : official journal of the American Society of Clinical Oncology 2026; JCO2601700 doi:10.1200/JCO-26-01700.

    PMID: 42462191
  17. 17

    Follow-up after treatment for breast cancer: Practical guide to survivorship care for family physicians.

    Sisler J, Chaput G, Sussman J, Ozokwelu E

    Canadian family physician Medecin de famille canadien 2016; (62(10)):805-811.

    PMID: 27737976
  18. 18

    American Cancer Society/American Society of Clinical Oncology Breast Cancer Survivorship Care Guideline.

    Runowicz CD, Leach CR, Henry NL, et al.

    CA: a cancer journal for clinicians 2016; (66(1)):43-73 doi:10.3322/caac.21319.

    PMID: 26641959
  19. 19

    Use of posttreatment imaging and biomarkers in survivors of early-stage breast cancer: Inappropriate surveillance or necessary care?

    Hahn EE, Tang T, Lee JS, et al.

    Cancer 2016; (122(6)):908-16 doi:10.1002/cncr.29811.

    PMID: 26650715

This page is for informational purposes only and does not replace medical advice. Your oncology team should interpret your symptoms, test results, and follow-up needs and tell you when to seek urgent care.

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