Medical Oncologist
Monitoring and tests
Tests and Monitoring — While You Are on Trastuzumab Deruxtecan
When your doctor orders tests before every cycle, it can feel unsettling. These checks are not a sign something has gone wrong — they are what allows problems to be caught early, while they are still manageable.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed August 2026
- Baseline first — A heart scan and blood tests before cycle one give your team a reference point for every result that follows.
- Blood tests before every cycle — Your white cell count and liver enzymes must be reviewed before each infusion.
- Lungs watched at every visit — Lung inflammation is the most significant known risk with this drug and can develop at any point — not only in the first few cycles.
- A flagged result is not a crisis — Many results lead to a short dose delay or adjustment rather than stopping treatment.
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Trastuzumab deruxtecan requires regular monitoring of your heart function, blood counts, liver enzymes and, most importantly, your lungs. Lung inflammation is the most significant risk associated with this drug, and your team will assess for its symptoms at every visit. NCCN and ESMO guidance requires these checks before each cycle.
How does monitoring work from your first appointment onwards?
Baseline assessment before your first dose
Before cycle one begins, you will have a heart scan (echocardiogram), blood tests covering your full blood count and liver enzymes, and a review of your breathing and any current symptoms. This baseline is what your team measures every later result against.
Blood tests and symptom check before every cycle
Before each infusion, blood count and liver results are reviewed. Your team will ask about any new symptoms — particularly cough, breathlessness or fever. If results are within the expected range, the cycle goes ahead.
Heart scan at set intervals
An echocardiogram to reassess your heart function is scheduled periodically — not before every cycle, but at intervals your oncologist sets. How often depends on your individual baseline and whether any changes appear.
Lung symptoms reviewed at every visit
Your team asks about breathing changes, new cough and fever at every appointment. If any of these develop between visits, you are expected to call the same day rather than wait. Lung monitoring runs for the full duration of treatment.
Results feed into the dose decision
After reviewing all results, your oncologist decides whether to proceed, adjust the dose, delay the next cycle, or pause treatment. A plan change is a normal part of managing treatment — not a sign the drug has stopped working.
Which symptoms should you report without waiting for your next appointment?
- New cough, or an existing cough that has clearly worsened
- Shortness of breath or breathlessness that is new or worse than usual
- Fever without an obvious cause
- Sudden or unusual tiredness that comes alongside any breathing change
- Yellowing of the skin or whites of the eyes
- Unusual bruising, prolonged bleeding from a minor cut, or nosebleeds
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Medical Oncologist
Dr. C. Raghavendra Reddy
MBBS(Gold Medal), DNB(General Medicine), DM(Medical Oncology)(Gold Medal)
Medical Oncologist
Dr. Bharati Devi Gorantla
MBBS, MD(General Medicine), DM(Medical Oncology)(Adyar,Chennai), ECMO, MRCP SCE(UK)
Medical Oncologist
Dr. Owais Mohammed
MBBS, MD (General Medicine), DrNB (Medical Oncology), ECMO, MRCP SCE (Medical Oncology) (UK)
Medical Oncologist
Medical Oncologist
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Dr. Muralidhar Muddusetty
MBBS (AIIMS), MS (Surgery) (AIIMS), DNB (Surgical Oncology), MRCS (Edinburgh)
Surgical Oncologist
Surgical Oncologist
Surgical Oncologist
Dr. Vinay Mamidala
MBBS, MS(General Surgery), M.Ch(Surgical Oncology), FMAS, FARIS(Ongoing)
Surgical Oncologist
Radiation Oncologist
Radiation Oncologist
Radiation Oncologist
Hematologist
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Dr. Mohammed Imran
Surgical Oncologist
Dr. Vajja Sandeep Kumar
MBBS, MS (General Surgery), DrNB (Surgical Oncology), FALS Oncology
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Why are your lungs watched more closely than anything else?
Your lungs are watched so closely because trastuzumab deruxtecan carries a known risk of interstitial lung disease — inflammation in the lung tissue that this drug can occasionally trigger. It is not common, but when it is caught late it can be serious.
NCCN and ESMO guidance classifies lung inflammation as the most clinically significant safety signal for this drug. Both bodies specify that lung symptom monitoring must continue at every cycle for the full duration of treatment, because ILD can develop at any point — not only in the early weeks.
This is why any new cough or breathlessness is worth a call on the day it appears, rather than waiting for your next scheduled appointment.
What does each test check for, and what does a concerning result mean?
| Test | When it is done | What the team is looking for | What a concerning result may lead to |
|---|---|---|---|
| Heart scan (echocardiogram) | Before starting, then at periodic intervals | Left ventricular ejection fraction — how efficiently the heart pumps | A significant drop may prompt a dose pause or referral to a cardiologist |
| Full blood count | Before every cycle | White cell count, platelets and haemoglobin | Low counts may delay the next cycle until levels recover to a safe level |
| Liver function tests | Before every cycle | Liver enzymes that signal stress or inflammation | Raised enzymes may need a dose hold or modification; usually reversible once the drug is paused |
| Lung symptom review | At every visit; any time new symptoms appear | New cough, breathlessness or fever that may indicate ILD | Prompt urgent assessment, usually including a CT scan of the chest |
| General side-effect review | At every visit | Nausea, vomiting and fatigue — severity and effect on daily life | Severe or persistent symptoms may lead to antiemetic adjustment or a change in dose timing |
Did you know?
Interstitial lung disease linked to trastuzumab deruxtecan can develop at any point during treatment — not only in the first few cycles. NCCN and ESMO guidance specifies lung symptom monitoring at every visit for the full duration of treatment because of this.
The single most important action in your hands between appointments is reporting any new cough or breathlessness on the day it appears.
Source: NCCN Guidelines for Breast Cancer; ESMO Clinical Practice Guidelines for Early and Metastatic Breast Cancer
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Common questions
Frequently asked questions
Do I need a heart scan before every cycle?
No. Blood tests are done before every cycle, but heart scans are scheduled at intervals — at baseline before you start, then periodically at points your oncologist sets. How often depends on your starting heart function and whether any results change during treatment. Your team will tell you when the next scan is due and will not leave you guessing about the schedule.
What is the echocardiogram checking for?
It measures your left ventricular ejection fraction — a figure that shows how efficiently your heart muscle is pumping blood with each beat. The antibody component of trastuzumab deruxtecan can affect heart muscle over time in a proportion of patients. Tracking your baseline and comparing later scans to it allows your team to respond before any change becomes significant. Most people do not develop a meaningful drop, but the monitoring exists because the consequences of a missed change are serious.
What happens if my blood count is too low to have my next cycle?
The next cycle will usually be delayed by a week or two to allow your counts to recover, rather than cancelled. This is called a dose delay and is a planned part of managing this treatment — it happens in a proportion of patients and is not a sign the drug has stopped working. Once your counts recover to the level your oncologist is looking for, treatment resumes, sometimes at the same dose and sometimes at a slightly adjusted one.
How likely is it that I will develop lung inflammation on this drug?
We do not give a single percentage here because any figure varies significantly by dose, prior history and other individual factors, and a number taken out of context can be misleading. What NCCN and ESMO consistently emphasise is that ILD is a recognised risk for all patients on trastuzumab deruxtecan, that monitoring is required at every cycle for this reason, and that early detection is what keeps it manageable. Reporting any new cough or breathlessness on the day it appears — rather than waiting — is the most important action in your hands.
Can I have my blood tests done locally rather than at the clinic?
Possibly, depending on where you are being treated and what your oncologist needs before the next cycle. Your doctor needs the results in hand before deciding whether to go ahead, so timing matters. Ask your team at CION which parts of your pre-cycle assessment can be done at a local collection point and which need to be at the treating centre. Do not assume local tests are acceptable without confirming first — the answer can vary between cycles.