Skip to main content

by Dr. C. H. Weaver M.D. updated 1/2023

On January 19, 2023, the Food and Drug Administration (FDA) granted accelerated approval to tucatinib Tukysa (tucatinib) in combination with Herceptin (trastuzumab) for the treatment of RAS wild-type HER2-positive unresectable or metastatic colorectal cancer that has progressed following chemotherapy.

Precision cancer medicines that target the HER2 receptor in breast, colon and other cancers represent an effective treatment option for individuals with HER2-positive (HER2+) disease. Researchers are evaluating various drug combinations that target the HER2 receptor in colorectal cancers because HER2 directed therapy is effective and can avoid the complications of chemotherapy.1-8

Patients have several treatment options. The most recently reported data is for Enhertu (trastuzumab deruxtecan), a HER2-directed antibody drug conjugate (ADC) precision cancer medicine, which delivers cytotoxic chemotherapy (“payload”) to cancer cells via a linker attached to a monoclonal antibody that binds specifically to the HER2 protein. Although active Enhertu was associated with significant toxicity resulting in excess mortality.10

About HER2-positive (HER2+) Colo-rectal Cancer

In the U.S. over 140,250 patients will be diagnosed with cancer of the colon or rectum in 2021, and approximately 50,000 are estimated to die of their disease.1 The HER2 receptor is a protein that is normally found on the surface of several different types of cells in the body but over expressed in multiple cancer types including ~4-5% of patients with colorectal cancer.2

The HER2 receptors span into the cell and are part a biologic pathway that is involved in cellular replication. Sometimes a gene that is responsible for the HER2 receptor becomes mutated, and too many receptors are produced. This, in turn, results in cells that divide and spread without their normal biologic controls. Cancer cells that have too many HER2 receptors are referred to as HER2-positive. Several precision cancer medicines have been developed that bind to different sites within the HER2 pathway resulting in decreased cell division and spread.2,3

Colon CancerConnect Community

Herceptin (trastuzumab) and Tykerb (lapatinib) are two precision cancer medicines that bind along the HER pathway at different points, both producing anti-cancer effects in HER2+ breast cancer. When evaluated in advanced HER2+ wild type KRAS patients with advanced colon cancer the combination is also active and well tolerated in treatment-refractory patients with HER2+ disease.3,4  Several other precision cancer medicines that target HER2 are in development and may be more effective than Herceptin and Tykerb

Tukysa - The MOUNTAINEER Clinical Trial

Tukysa (tucatinib) is a tyrosine kinase inhibitor drug that is highly selective for HER2 without significant inhibition of EGFR. EGFR inhibition is associated with significant side effects including skin rash and diarrhea.

The single arm phase 2 clinical trial known as MOUNTAINEER evaluated the effectiveness of combination HER2 therapy with Herceptin combined with Tukysa in HER2+ advanced colorectal cancer in patients with HER2+ RAS wild-type metastatic colorectal cancer after treatment with first- and second-line standard-of-care therapies. 

Late-breaking data from The pivotal phase 2 MOUNTAINEER clinical trial evaluating TUKYSA® in combination with Herceptin (trastuzumab) were presented in an oral session at the European Society for Medical Oncology (ESMO) World Congress on Gastrointestinal Cancer on July 2, 2022 in Barcelona, Spain. 

Scroll to Continue

Recommended Articles

Prostate Cancer

Treatment for Recurrent Prostate Cancer

Cancer Connect - Treatment for Recurring Prostate Cancer

Image placeholder title

FDA - Breast Implants Linked to Development of Anaplastic Lymphoma

Breast implants associated with risk of rare lymphoma cancer

Image placeholder title

Treatment of Early Stage Breast Cancers

Comprehensive Review of Treatment for Early Stage I - III Breast Cancer

At a median duration of follow-up of 20.7 months results of the trial showed a 38% confirmed objective response rate. In these patients, the median duration of response was 12.4 months and median overall survival was 24.1 months. At study entry, 64.3% and 70.2% of these patients had liver or lung metastases, respectively, and had received a median of 3.0 (1-6) prior lines of systemic therapy.

Herceptin-Perjeta (pertuzumab) Combination

The combination of Herceptin-Perjeta also has demonstrated promising activity in patients with metastatic CRC with RAS wild-type and HER2 amplification in the TRIUMPH clinical trial. Overall ~35% of 19 patients with RAS wild-type and HER2-amplified metastatic CRC that were refractory to standard chemotherapy responded to treatment. With the combination some treatment-related cardiac and infusion related side effects were reported.

  • Higher HER2 expression as measured by immunohistochemistry score (3+ versus 2+) appears to be associated with greater response rates and delayed cancer progression.
  • The identification of clonal oncogenic ctDNA driver mutations, such as KRAS, BRAF, PIK3CA, or HER2 appeared to predict for resistance to treatment.


Enhertu (trastuzumab deruxtecan) is a HER2-directed antibody drug conjugate (ADC) precision cancer medicine, which delivers cytotoxic chemotherapy (“payload”) to cancer cells via a linker attached to a monoclonal antibody that binds specifically to the HER2 protein. When Enhertu binds, it delivers its attached novel topoisomerase I inhibitor (DXd) chemotherapy payload. It is designed to deliver enhanced cell destruction upon release inside the cell and to reduce systemic exposure to the chemotherapy when compared to the way chemotherapy is commonly delivered.

The Phase II DESTINY-CRC01 clinical trial evaluated Enhertu in unresectable or metastatic HER2-expressing colorectal cancers and the results were update at ASCO 2022. Researchers looked at Enhertu in 3 groups of previously treated colorectal cancer patients. A HER2-positive group, which included individuals with HER2 expression scores of 3 or higher according to immunohistochemistry testing, and two HER2-low expressing groups, in which patients had IHC scores of 1 and 2.

HER2-positive, IHC3 patients experienced a response rate of 45% to Enhertu; 24 patients had a partial response, but no patients had a complete response. The median duration of response was seven months and median duration of overall survival was 15.5 months. No partial or complete responses were observed in HER2-low expressing patients. 

Drug-induced pneumonitis/interstitial lung disease occurred in 9% of patients with a 3.5% fatality rate. This serious adverse event developed at a median of 61 days from drug initiation. In the three fatal cases, the median time was 20 days, with death on average six days after symptoms.  Enhertu is currently FDA approved for the treatment of gastric and breast cancer.10

Patients with advanced colorectal cancer should undergo genomic testing and evaluation for HER2 over expression or amplification. Genomic testing can determine if patients have HER2+ cancers or other targetable mutations. Those with HER2+ disease discuss the role of precision cancer medicines that target the HER2 receptor with their oncologist. 

Colon Newsletter


  1. American Cancer Society, Cancer Facts and Figures 2018-2019.
  2. Loibl S, Gianni L (2017). HER2-positive breast cancer. The Lancet 389(10087): 2415-29.
  3. Slamon D, Clark G, Wong S, et al. (1987). Human breast cancer: correlation of relapse and survival with amplification of the HER-2/neu oncogene. Science 235(4785): 177-82.
  4. Sartore-Bianchi A, Trusolino L, Martino C, et al. Dual-targeted therapy with trastuzumab and lapatinib in treatment-refractory, KRAS codon 12/13 wild-type, HER2-positive metastatic colorectal cancer (HERACLES): a proof-of-concept, multicentre, open-label, phase 2 trial. Lancet Oncology. Published online April 20, 2016. DOI: [access here]( Accessed May 10, 2016.
  5. Strickler JH, Zemla T, Ou F-S, et al. Trastuzumab and tucatinib for the treatment of HER2 amplified metastatic colorectal cancer (mCRC): Initial results from the MOUNTAINEER trial.
  6. Nakamura Y, Okamoto W, Kato T, et al. TRIUMPH: Primary Efficacy of a Phase II Trial of Trastuzumab (T) and Pertuzumab (P) in Patients (pts) with Metastatic Colorectal Cancer (mCRC) with HER2 (ERBB2) Amplification (amp) in Tumor Tissue or Circulating Tumor DNA (ctDNA): A GOZILA Sub-study.
  7. 3505.doi:10.1200/JCO.2021.39.15_suppl.35