Tucatinib Plus Trastuzumab in Patients With HER2+ Colorectal Cancer

Inclusion Criteria

* Histologically and/or cytologically documented adenocarcinoma of the colon or rectum that is metastatic and/or unresectable
* Unless contraindicated, participants must have received and failed regimens containing the following agents: fluoropyrimidine (e.g., 5-fluorouracil or capecitabine), oxaliplatin, irinotecan, an anti-VEGF monoclonal antibody (bevacizumab, ramucirumab, or ziv-aflibercept), and an anti-PD-(L)1 therapy (nivolumab or pembrolizumab) if tumor has deficient mismatch repair proteins or is MSI-High.
* Have progression of unresectable or metastatic CRC after the last systemic therapy, or be intolerant of last systemic therapy
* Have RAS wild-type in primary or metastatic tumor tissue, based on expanded RAS testing
* Willing and able to provide the most recently available tissue blocks obtained prior to treatment initiation. If archival tissue is not available, then a newly-obtained baseline biopsy of an accessible tumor
* Have confirmed HER2-positive mCRC, as defined by having tumor tissue tested at a Clinical Laboratory Improvement Act (CLIA)-certified or International Organization for Standardization (ISO)-accredited laboratory, meeting at least one of the following criteria:

  * HER2+ overexpression (3+ immunohistochemistry \[IHC\]) by an FDA-approved or Conformité Européene (CE)-marked HER2 ICH test
  * HER2 2+ IHC is eligible if the tumor is amplified by an FDA-approved or CE-marked HER2 in situ hybridization assay (FISH or chromogenic in situ hybridization \[CISH\]))
  * HER2 (ERBB2) amplification by CLIA-certified or ISO-accredited next generation sequencing (NGS) sequencing assay
* Have radiographically measurable disease assessable by RECIST 1.1, with at least one site of disease that is measurable and that has not been previously irradiated; or, if the participant has had previous radiation to the target lesion(s), there must be evidence of progression since the radiation
* Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0, 1, or 2
* Life expectancy greater than 3 months
* Have adequate hematological, hepatic, renal, coagulation, and cardiac function

Exclusion Criteria

* Previous treatment with anti-HER2 targeting therapy
* Previous treatment with any systemic anticancer therapy, non-central nervous system radiation, or experimental agent within 3 weeks of first dose of study treatment
* Toxicity related to prior cancer therapies that has not resolved to ≤ Grade 1, with the following exceptions:

  * Alopecia and neuropathy, which must have resolved to ≤ Grade 2
  * Congestive heart failure (CHF), which must have been ≤ Grade 1 in severity at the time of occurrence, and must have resolved completely
  * Anemia, which must have resolved to ≤ Grade 2
  * Decreased ANC, which must have resolved to ≤ Grade 2
* Have clinically significant cardiopulmonary disease
* Have known myocardial infarction, unstable angina, cardiac or other vascular stenting, angioplasty, or cardiac surgery within 6 months prior to first dose of study treatment
* Major surgical procedure, open biopsy, or significant traumatic injury ≤28 days prior to enrollment (≤56 days for hepatectomy, open thoracotomy, or major neurosurgery) or anticipation of need for major surgical procedure during the study
* Serious, non-healing wound, ulcer, or bone fracture
* Known to be positive for hepatitis B by surface antigen expression
* Known to have active hepatitis C infection

  * Exception for participants with a documented sustained virologic response of 12 weeks
* Known to be positive for human immunodeficiency virus (HIV)
* Subjects who are pregnant, breastfeeding, or planning a pregnancy
* Inability to swallow pills or any significant gastrointestinal disease which would preclude the adequate oral absorption of medications
* Have used strong CYP2C8 inhibitor within 5 half-lives of the inhibitor, or have used a strong CYP2C8 or CYP3A4 inducer within 5 days prior to first dose of study treatment
* History of another malignancy within 3 years before the first dose of study drug, or any evidence of residual disease from a previously diagnosed malignancy.

  * Exceptions are malignancies with a negligible risk of metastasis or death
* Subjects with known active CNS metastasis

  * Irradiated or resected lesions are permitted, provided the lesions are fully treated and inactive, subject is asymptomatic, and no steroids have been administered for at least 30 days