What the label lists and what reports show
Tucatinib side effects
Tucatinib's FDA label: “The most common adverse reactions (≥20%) with TUKYSA in combination with trastuzumab and capecitabine in patients with metastatic breast cancer are diarrhea, palmar-plantar erythrodysesthesia, nausea, hepatotoxicity, vomiting, stomatitis, decreased appetite …” FAERS holds 6,932 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is diarrhoea (1,766 reports).
- No generic listed
Check it at the source: the tucatinib FDA label on DailyMed (effective November 4, 2024, SEAGEN INC.); the FDA FAERS public dashboard.
What does the patient leaflet say about side effects?
From the patient leaflet: What are the possible side effects of TUKYSA?TUKYSA may cause serious side effects, including: • Diarrhea. Diarrhea is common with TUKYSA and can sometimes be severe. Tell your healthcare provider if you have a change in your bowel movements or severe diarrhea. Severe diarrhea can lead to loss of too much body fluids (dehydration), low blood pressure, kidney problems and death. Your healthcare provider may prescribe medicines to treat your diarrhea during treatment with TUKYSA. • Liver Problems. TUKYSA can cause severe liver problems. Your healthcare provider will do blood tests to check your liver function before and every 3 weeks during treatment with TUKYSA, or as needed. […]
Source: FDA drug label, SEAGEN INC., effective November 4, 2024 (SPL set f27eb1b9-b7fc-424e-988f-84dd7bb195a3), via openFDA; the full label on DailyMed
What does the label list?
From the label: adverse reactionsThe most common adverse reactions (≥20%) with TUKYSA in combination with trastuzumab and capecitabine in patients with metastatic breast cancer are diarrhea, palmar-plantar erythrodysesthesia, nausea, hepatotoxicity, vomiting, stomatitis, decreased appetite, anemia, and rash.
Table 5: Adverse Reactions (≥10%) in Patients with Unresectable or Metastatic Colorectal Cancer (MOUNTAINEER)
| Reaction | Adverse Reaction All Grades % | TUKYSA + Trastuzumab N= 86 Includes 1 patient who only received trastuzumab. Grade 3 % |
|---|---|---|
| Diarrhea | 64 | 3.5 |
| Nausea | 35 | 0 |
| Vomiting | 16 | 0 |
| Abdominal pain Abdominal pain includes abdominal discomfort, abdominal pain, and… | 21 | 2.3 |
| Constipation | 14 | 1.2 |
| Fatigue | 44 | 2.3 |
| Pyrexia | 20 | 0 |
| Chills | 19 | 1.2 |
| Rash Rash includes acne, dermatitis acneiform, dermatitis contact, erythema, erythema… | 37 | 0 |
| Infusion related reaction | 21 | 0 |
| Decreased appetite | 19 | 0 |
| Anemia | 10 | 0 |
| Hypertension | 17 | 7 |
| Back pain | 17 | 2.3 |
| Arthralgia | 16 | 1.2 |
| Myalgia | 13 | 0 |
| Cough | 16 | 0 |
| Dyspnea | 14 | 0 |
| Anxiety | 10 | 0 |
Rows and numbers as the label prints them, under its own column headings (the first rows of a longer table where it runs on). A reaction in a trial table is not necessarily caused by the medicine, and trials differ from everyday use.
From the label: adverse reactions, continuedThe following clinically significant adverse reactions are described elsewhere in the labeling: • Diarrhea [see Warnings and Precautions (5.1) ] • Hepatotoxicity [see Warnings and Precautions (5.2) ] • The most common adverse reactions (≥20%) with TUKYSA in combination with trastuzumab and capecitabine in patients with metastatic breast cancer are diarrhea, palmar-plantar erythrodysesthesia, nausea, hepatotoxicity, vomiting, stomatitis, decreased appetite, anemia, and rash. ( 6.1 ) • The most common adverse reactions (≥20%) with TUKYSA in combination with trastuzumab in patients with unresectable or metastatic colorectal cancer are diarrhea, fatigue, rash, nausea, abdominal pain, infusion related reactions, and pyrexia. To report SUSPECTED ADVERSE REACTIONS, contact Seagen at 1-855-4SEAGEN or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch. 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. HER2-Positive Metastatic Breast Cancer The safety of TUKYSA in combination with trastuzumab and capecitabine was evaluated in HER2CLIMB [see Clinical Studies (14) ]. …
Source: FDA drug label, SEAGEN INC., effective November 4, 2024 (SPL set f27eb1b9-b7fc-424e-988f-84dd7bb195a3), via openFDA; the full label on DailyMed
What do FAERS reports show?
6,932 reports list tucatinib among the medicines taken, each a report of something that happened, not proof the medicine caused it; 708 are coded as a death and 1,881 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 12 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.
Reports received each year
The 25 most reported reactions
Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms
What next?
- Tucatinib: the full record
- label, generics, price, shortages, recalls
- Report a side effect to the FDA
- MedWatch
- Side effects hub
- the most reported medicines and reactions